IGCSE Coordinated Science- Physics

P1.1 Motion 1 Define speed and calculate speed from:

Speed = Distance/Time

The speed of an object is the distance it travels per unit time. We quantify this as the ratio of the distance it travels to the time taken to travel that distance.

The formula for speed is above and the units are ms-1 or m/s.

Ex. Michael runs a marathon. He runs 40km in 2 hours. What is his average speed?

Well, the distance Michael travels is 40km. He does this in 2 hours. Therefore, using the formula Speed= Distance/Time, we get:

Speed = 40km/2hours

= 20km/ hour

2 Distinguish between speed and velocity.

We don’t really touch upon this during GCSE, but it doesn’t hurt to get some additional knowledge.

Basically, speed and velocity are both different type of quantities. The two types of quantities are:

• Vector • Scalar Vector quantities have both a magnitude and direction. Scalar quantities only have a magnitude but no direction. That is the fundamental difference between velocity and speed. Velocity is a vector whilst speed is a scalar. Velocity not only measures how

fast something travels, but also the direction it is traveling in, something the speed neglects.

3 Plot and interpret a speed/time graph and a distance/time graph.

It is often useful to be able to map the relations between speed, distance and time graphically.

The graph below will show a speed/time graph where we measure how speed is changing according to time.

• Speed/Time Graph

Green line: Constant acceleration.

Orange Line: If you look at the y-axis, speed doesn’t change, so we can say the object is travelling with a constant speed.

Blue line: Object is now decelerating, in which change in velocity is now a negative value.

• Distance/Time Graph

Notes:

Green line: Speed of the object is constant, and can be found by dividing Distance by Time. We can tell speed is positive as both time and distance travelled are also both positive.

Orange line: Distance is not changing so object remains stationary with no movement.

Blue line: Steady speed returning to the start.

The red line is steeper than the green line, so therefore it is travelling at a faster speed. Steepness is basically a measure of the gradient of the Distance/Time graph, which is also the speed of an object. The steeper the graph, the higher the gradient, and therefore the faster the speed.

4 Recognize linear motion for which the acceleration is constant and calculate the acceleration.

The situation above mainly shows cases where the acceleration is constant. We can test that this is true by finding the gradient of the line. We can find the distance simply by dividing Change in speed by Time, which if you look carefully enough, is the formula for

acceleration. Here, we say that the speed is proportional to time and that acceleration (the gradient) is constant throughout the journey.

5 Recognise motion for which the acceleration is not constant.

In Q5, we learned how to calculate acceleration when it is a constant value on a Speed/time graph.

However, in the real world, this is rarely the case. Rarely can you accelerate with “constant” velocity and more likely than not, the acceleration of an object is going to change around a bit. Here is an example of a graph where the gradient is not constant.

Notice when the speed/time graph is not a straight line (proportional relation), then the acceleration is not constant. You just have to be able to appreciate this fact, and will not be asked to make any calculations. However, in IB/A-level math, you will have to make these quite pointless calculations

6 Calculate the area under a speed/time graph to work out the distance travelled for motion with constant acceleration

Using the given information above, you can easily calculate the distance travelled.

Remember the formula Speed= Distance/Time

If we re-arrange the formula, we get Distance = Speed x Time.

Notice here, Speed x Time is equivalent to the area of the graph.

Let’s calculate the distance travelled. It’s simply the area under the shaded orange triangle.

Now, we simply have to apply some simple mathematical skills.

What’s the area of a triangle?

Area of Triangle = (Base x Height)/2

Base = Time = 8 seconds

Height = Speed = 10meter/second

(Base x Height)/2 = (8 secondsx10 meters/second)/2

=40 meters.

7 Demonstrate a qualitative understanding that acceleration is related to changing speed.

Acceleration is the measure of the change of speed of an object per unit time, more specifically, the velocity of the object, and we’ve

definitely talked about their differences.

P2.1 Mass and Weight

1. Difference between Mass and Weight

• Weight is the gravitational pull on an object measured in Newtons because it is the amount of the force. This is different on different planets because the gravitational pull is different because of the different mass of the planet.

• Mass is the amount of particles in a substance. This is the same regardless of how much gravitational pull is applied to the object because the amount of particles of in an amount of substance.

The weight is the gravitational constant multiplied by the mass.

2. Demonstrate understanding that mass is a property that ‘resists’ change in motion. This is the concept of inertia. If a force is applied to an object, it will not immediately reach a high speed because it requires time to accelerate. F=MA. If the force is constantly applied then there is a constant acceleration. However if the force is not constant and only applied in an instant then there will be an instant of acceleration and then it will take time for the object to speed up.

3. Know that the Earth is the source of a gravitational field. Gravity is an attractive force created by the presence of mass. Any object with a mass with have a gravitational field. The more mass an object has the stronger the gravitational energy it holds.

4. Describe, and use the concept of, weight as the effect of a gravitational field on a mass. As mentioned before the weight of an object is the gravitational force applied onto it multiplied by the mass.

W = m x g (N) = (kg) (m/s²)

P2.1 Density 1 Describe an experiment to determine the density of a liquid and of a regularly shaped solid and make the necessary calculation using the equation:

Density = Mass/Volume or D = m/v.

Dead simple. Simply find the mass by weighing the thing on a scale and then use a measuring cylinder to find the volume. Then divide the mass by the volume to get the density in (g/cm³)

2 Describe the determination of the density of an irregularly shaped solid by the method of displacement, and make the necessary calculation.

If you want to find the density of an irregular solid, the volume can be found using a displacement (Eureka) can. First the can is filled to the level of the spout, then the solid is lowered into the water. The water collected out of the spout is poured into a measuring cylinder and that is the volume of the solid. Then, you just have weigh the mass and then apply the density formula to get the answer.

P2.3 Effects of Forces

1 Know that a force is measured in newtons (N).

Force is normally measured in the SI unit of Newtons.

2 Describe how forces may change the size, shape and motion of a body.

F=ma, Newton’s second Law basically states that the Force of an object is proportional to its acceleration. Increasing the force will increase the acceleration of an object, and thus will have an effect on the motion of an object.

F=mg basically states that the force of an object equals the mass of the object multiplied by the gravitational force. As we can see from the formula, increasing the force will increase the mass as G-force is usually a constant, so the force on an object will definitely alter the size of an object.

3 Plot extension/load graphs and describe the associated experimental procedure.

Procedure

http://www.4physics.com/phy_demo/HookesLaw/HookesLawLab.html

4 Interpret extension/load graphs.

Refer back to the graph above. Extension is on the X-axis and Load is on the Y-axis. What the graph is ultimately suggesting is that as you increase Extension, the load increases proportionally. However, at the curved bit, the spring has reached its limit of proportionality, which we will discuss in a second.

If you don’t get a nice straight line when plotting results in an extension/load graph, prepare to accept that you blundered and be sure to go back to check that you plotted the points correctly.

5. State and use Hooke’s Law and recall and use the expression Force = constant x extension (F = k x).

Basically, the graph above follows something called Hooke’s Law, which basically states that the force is proportional to the extension.

The equation for Force is therefore F = kx where k = constant and x= extension.

6. Recognise the significance of the term limit of proportionality for an extension/load graph.

Hooke’s Law states that the Force is proportional to the Extension. HOWEVER, this is only up to a certain limit. Proportionality means that if you were to plot this on a graph, you would get a straight line, and if you look above, the graph is linear (straight line), but if you notice, when Extension reaches a certain value, the graph starts to curve a bit. Yes, I didn’t draw this wrong. After a certain amount of extension, the string reaches the limit of proportionally, where if you extend the spring any further, Force will no longer be proportional to extension, and on a graph, you will see just like the one above, a curve indicating that the limit of proportionality has been reached.

7 Recall and use the relation between force, mass and acceleration (including the direction).

The relationship between this was actually discovered by this guy called Issac Newton.

F= Force (N)

m = mass

a= acceleration

8. Find the resultant of two or more forces acting along the same line.

• Force is assigned a magnitude with value “x” Newtons, x being the actual magnitude. We often see two forces acting against each other. We want to find the “Resultant Force” of these two forces acting together, and we can simply do this by subtracting the smaller force by the larger one.

Here is an example below:

The larger force = 350N

The smaller force= 50N

Resultant force = larger force – smaller force = 350N-50N = 300N, pointing to the right, as the larger force’s arrow is pointing to the right.

9. Explain how a system is in equilibrium when there is no resultant force

A system is in equilibrium mainly when both opposing forces are equal in magnitude and the resultant force is 0.

An example below:

The force on the left = force on right, so if you were to subtract the two vectors to find a resultant force, as they are both 350N, you will get:

Resultant Force = 350N-350N

=0N

Which basically means the system is in equilibrium and there is no resultant/overall force and both the vectors cancel each other out.

P2.4 Pressure 1 Relate (without calculation) pressure to force and area.

Pressure is simply the force exerted divided by the area the pressure is exerted on.

2 Recall and use the equation P = F/A.

I’m just going to do some GCSE style questions which I will update quite regularly.

Pressure = Force ÷ Area

Force measured in Newtons

Area measured in square meters

So pressure is measured in : Pascals (Pa)

1) An office table has a weight of 600N. If the area of the base is 3.0 sq metres, what is the pressure on the floor of the office?

This question is dead simple. Simply take the Force (600N) and divide by the area (3.0 sq metres) to get

600N/3 sqmetres

=200 Pa

P3.1 Energy 1 Know that energy and work are measured in joules (J), and power in watts (W).

The energy of an object is measured in Joules (J). 1000 Joules = 1kilojoule (kJ)

The power of an object is measured in Watts (W). 1000 Watts=1kilo Watt (kW)

2 Demonstrate understanding that an object may have energy due to its motion (kinetic) or its position (potential), and that energy may be transferred and stored.

All objects have what we call, internal energy in its molecules. Internal energy is made out of Kinetic Energy (due to the motion of the molecules), and Potential Energy(due to the position of the object).

You can’t create or destroy energy, energy is conserved. However, energy can be transferred and stored. For example, when you jump of a cliff (god forbid), the Potential Energy will slowly be converted to Kinetic Energy. The NET Energy remains the same, but you see a transfer of energy from one form to another.

3 Recall and use the expressions: K.E. = ½ mv2 and P.E. = mgh

Kinetic Energy (J) = 1/2 x Mass x Velocity Squared

Potential Energy (J) = Mass x Gravitational Force x Height

4 Give and identify examples of energy in different forms, including kinetic, gravitational, chemical, strain, nuclear, thermal (heat), electrical, light and sound.

Kinetic Energy

I guess anything that is in motion has some sort of kinetic energy. Examples include:

• Running a marathon • A ball falling off the cliff. Gravitational Potential Energy.

This is the energy that exists due to the position of the object.

A good example is:

• A man standing on a cliff will have gravitational potential energy. Chemical Energy

This is the energy in a substance that gives the substance potential to undergo a chemical reaction.

A good example is:

• Chemical Energy in a battery. Strain Energy

Strain energy is released when the constituent atoms are allowed to rearrange themselves in a chemical reaction or a change of chemical conformation in a way that:

A good example is:

• Energy in an elastic band. Nuclear Energy

• Nuclear bombs (unsurprisingly), have nuclear energy. Thermal Energy

• Sweating after a run • Heat released after cooking some rice.

Electrical Energy

• Turning on your TV requires electrical energy. Sound

• Sound from microphones can be passed off as sound energy. Light • Turning on a lightbulb. 5 Give and identify examples of the conversion of energy from one form to another, and of its transfer from one place to another.

• In a battery, chemical energy changes into electrical energy. • In a wind turbine, wind is transformed into mechanical energy .

Then attached to a transformer where energy is then transformed into electrical energy.

• Nuclear energy is transferred into heat and electrical energy in a nuclear plant.

• When a ball falls off a cliff, gravitational potential energy is being transferred into kinetic energy.

6 Apply the principle of energy conservation to simple examples

We discussed this briefly just now. The Principle of energy conservation states that “energy can neither be created nor destroyed”.

A really good example can be seen when we throw a ball of a cliff.

When the ball is at the top of the cliff, its Gravitational Potential Energy is at its highest, as GPE = mgh and “h” is at its maximum at the top of the cliff. However, when you throw the ball off the cliff, you may think that as “height” is decreasing, the GPE of the ball is also decreasing. As a result, the total energy of the ball must be decreasing as well right?

Wrong.

As the ball falls, the energy it loses as Gravitational Potential Energy is being transferred into another form of energy, kinetic energy, and the amount transferred is the exact same as the amount lost via Gravitational Potential Energy.

P3.2 Energy Resources

1 Distinguish between renewable and nonrenewable sources of energy.

Renewable sources of energy, just like it sounds, are resources that theoretically can be used for ever if used at a rate which is consistent with the rate in which it is replenished. Examples include solar, wind and water energy. Every day, the sun comes out and we can indefinitely use its energy—for the time being at least.

Non-Renewable sources of energy are resources that get exhausted when used, and basically when you use all of them, that’s it, they’re gone. Examples include fossil fuels, oil and coal.

2 Demonstrate understanding that energy is released by nuclear fusion in the Sun.

This is quite a simple concept:

• Particles “fuse” together, which basically means they join to each other.

• Two hydrogen atoms fuse to produce a helium atom. • Helium has slightly less mass than the hydrogen’s, so the lost mass

is converted to energy . • The helium atoms then fuse to produce heavier elements to

constantly release energy. This constantly release of energy is why the sun shines and is able to provide the earth with sunshine and heat. Obviously, its not that simple but you get the gist. 3 Know that the Sun is the source of energy for all our energy resources except geothermal and nuclear.

Yeah, so just remember that OTHER than Geothermal and Nuclear energy, the sun is our king. 4 Describe how electricity or other useful forms of energy may be obtained from: • Chemical energy stored in fuel, • Water,

including the energy stored in waves, in tides, and in water behind hydroelectric dams, • Geothermal resources, • Nuclear fission, • Heat and light from the Sun (solar cells and panels).

Chemical Energy stored in fuel

• Burn the chemical fuel to produce heat. • The heat is then used to heat a liquid such as water which is then

turned into steam. • The pressure from the steam is used to spin a turbine, and it is this

spinning that produces electricity Tidal • Underwater turbines spin like windmills • The turbines are mounted on a gearbox shaft, which generated

electricity. • Underwater cables then help carry the electricity to the shore. Wave • The movement of sea water in and out of the shore compresses the

trapped air and drives a turbine. Geothermal • Possible to use the natural heat of the earth to generate electricity. • Cold water is first pumped underground. • The cold water then comes out as steam. • This steam can be used for heating or powering turbines to create

electricity. Nuclear Fission

• Electricity can be generated through nuclear fission. During nuclear fission, energy is released, and electricity can be produced in the Nuclear Reactors.

Heat and light from the Sun (solar cells and panels). • Heat from the sun is trapped in solar panels and subsequently

converted into electricity. 5 Give advantages and disadvantages of each method

Chemical

• Pros: • Ready made and available

• Relatively cheap • Cons: • Gives off pollutants which can be damaging to the environment. • Non-renewable. Tidal • Pros: • Has potential to generate alot of energy • Very reliable as it is quite easy to predict when is there going to be

a low and high tide. • Renewable, so can be continued to be used for a long time. • Little environmental impact. • Cons: • Initial costs of building dams are extremely high. • Affects transportation system in the water. • Affect ecosystem surrounding the dam.

Wave • Pros: • Clean • Renewable energy source • Does not have damaging effects on environment • Doesn’t need fuel so more cost-effective. • Few safety risks • There is a lot available. • You can potentially generate alot of energy. • Cons: • Getting alot of power is often difficult. • Not a very popular method at the moment, so may be very

expensive. • Waves vary in size so you may not always to be able to generate

electricity. Geothermal • Pros: • Potentially unlimited supply of energy. • Little impact on the environment. • Renewable–can be reused.

• Cons: • Can be expensive

• Only works in area with volcano activity. • There may be little volcanic activity, making power stations

unnecessary.

Nuclear Fission • Pros: • Small amount of radioactive material can release a lot of energy. • Relatively cheap. • Can last a long time. • Doesn’t give off pollutants. • Cons: • Expensive • Highly toxic and must be stored for a long period of time. Costs for

storage are also high. • Nuclear leakage can have significant impact on the people and

environment. Examples include: Chernobyll 1986 and the Japan nuclear disaster in Fukushima.

Heat and light from the Sun (solar cells and panels). • Pros: • Potentially infinite supply of energy. • Little environmental impact. • Renewable. • Cons: • May be costly to install solar panels. 6 Recall and use the equation:

Basically, what this equation does is it determines how ‘efficient’ a system is. For example, if you have a machine which releases 6000J of energy, but 3000J is lost to the environment.

The amount of useful energy will therefore be only 6000J-3000J = 3000J

As the total energy output is 6000J

The efficiency will therefore be:

(3000/6000)*100%

= 50%

*In the exam, there is a great way to validate your answers. If you get a ridiculous percentage, let’s say 777%, you can safely assume you’re wrong.

P3.3 Work P1 Relate (without calculation) work done to the magnitude of a force and the distance moved.

If a constant force of lets say, magnitude F, acts on a point that moves distance s,in the same direction of the force, then the Work is simply the force multiplied by the distance s.

P2 Describe energy changes in terms of work done.

Work is the amount of energy transferred into or out of a system, not counting energy transferred by heat conduction.

Needs expanding.

P3 Recall and use W = F × d.

This is just the formula Work = Force x Distance.

P4.1 States of Matter P1 State the distinguishing properties of solids, liquids and gases.

DIFFERENCES BETWEEN SOLID, LIQUIDS AND GASES solid gas liquid

retains a fixed volume and shape

rigid – particles locked into place

assumes the shape and volume of its

container particles can move past one another

assumes the shape of the part of the container which it

occupies particles can

move/slide past one another

not easily compressible

particles have little space in between

them.

It is compressible. large gaps

between particles

not easily compressible

little free space between particles

does not flow easily

rigid – particles cannot move/slide past one another

flows easily particles can move past one another

flows easily particles can

move/slide past one another

P4.2 Molecular Model 1 Describe qualitatively the molecularstructure of solids, liquids and gases.

Solids

• Particles are close together, help together by strong intermolecular forces.

• Particles vibrate around a fixed point, so has little freedom of movement.

Liquids

• Particles are also quite close together, but the forces are not as strong as that of those in solids.

• The liquid takes the shape of its container.

Gases

• Particles are far apart from each other and bounce around randomly in the container.

• Intermolecular forces between particles are pretty weak. 2 Relate the properties of solids, liquids and gases to the forces and distances between molecules and to the motion of the molecules

Solid

Distance between particles are very close together, as witnessed by the diagram above.

Liquid

The distance here is not as close as that of the solids, but the particles are still quite close together, and the forces between the particles are still quite strong.

A liquid, because the particles can move and slide over each other, liquids fill the shape of its container.

Gas

Particles are very far apart here. Again, this can be seen through the diagram.

Because particles are not in place, gases can flow like a liquid.

3 Interpret the temperature of a gas in termsof the motion of its molecules.

The temperature of a substance is proportional to the kinetic energy of the molecules. If the temperature of the gas increases, it will have more kinetic energy ,and will move around faster and obviously, particles will have more energy.

4 Describe qualitatively the pressure of a gasin terms of the motion of its molecules.

Firstly, what is pressure?

Pressure is the force exerted by a substance per unit area on another substance.

Let’s take a balloon as an example.

If you blow into a balloon, the balloon expands because there is a greater pressure inside the balloon than outside.

So, how can we describe pressure in terms of molecules?

The motion of molecules in a substance causes the collision of these molecules on the wall of the container. This exerts a force on the walls of this container, which we define as pressure.

5 Describe qualitatively the effect of a changeof temperature on the pressure of a gas atconstant volume.

Let’s use a quantitative description to describe this:

PV = nRT

Let’s forget about nR here, so what we’re dissecting is basically:

PV = T

PV = T

Volume is constant

So as we can see from this formula, Pressure and Temperature are proportional.

We call this relation the Guy Lussac’s Law

If the gas has more kinetic energy in its molecules, pressure increases as it hits the container with more kinetic energy.

If you decrease the volume of the container, the pressure increases as the number of particles hitting each cm3 of the container wall will increase.

Look at the diagram below:

The particles are hitting the containers randomly. And you have to admit, there is quite alot of wall-space for the particles to hit at. The Pressure here is quite low as we can see that the number of particles that will hit the walls of container each second will not be too high (low frequency), and that is how we determine pressure. However, what happens when we decrease the volume by half?

The particles are definitely going to hit the walls of the container more frequently, so the pressure is going to increase.

P4.3 Evaporation Evaporation mostly occurs at the surface of a liquid, and for evaporation to occur, the molecules must have enough kinetic energy.

First, let’s define the word Evaporation. Evaporation is basically the change of state of a substance from liquid to gas. If you look back into the Topic “States of Matter”, you will notice that the particles in a liquid are stuck quite close together, where’s the particles in a gas is scattered all over the place. Evaporation makes the particles in a liquid behave like the particles in a gas.

However, in order to break the relatively strong bonds holding the particles together in a liquid, energy is required to allow the molecules to become more energetic, and allow some particles to overcome the bonds holding the liquid particles together and become a gas. Some molecules have more energy than others, so become a gas more quickly.

2 Demonstrate understanding of how temperature, surface area and air flow over a surface influence evaporation.

Flow rate of air: This is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with

time, thus encouraging faster evaporation.

Temperature: If substance has higher temperature, molecules will have a higher average kinetic energy, and hence the rate of evaporation will increase.

3 Relate evaporation to the consequent cooling.

Evaporation is one of the four principal ways that heat can be transferred (the other three are radiation, convection, and conduction). Evaporation of sweat from the skin is an endothermic reaction: the reaction essentially “consumes” heat, which cools the body in the process.

For a liquid to turn into gas, either by boiling or evaporation, energy is required. This is known as the latent heat of vapourisation. In the case of boiling this is provided by external heat sources but in the case of evaporation it has to come from within the liquid itself, thus cooling it.

The energy is required to break the strong bonds between the molecules in the liquid and allow them to break free in gaseous form. Evaporation is an endothermic (heat-absorbing) process because molecules must be supplied with energy to overcome the intermolecular forces.

Evaporation occurs at the surface of a liquid, and energy is required to release the molecules from the liquid into the gas. The use of this energy, known as latent heat, causes the temperature of the liquid to fall.

Evaporation cools the surface of the thing that the liquid is evaporating from. Reason being evaporation is the departure of the warmest and most active (energetic) particles because they are the ones with enough energy to ‘escape’ into the air. Which leaves behind the cooler, less energetic particles, which brings down the average temperature of what’s left behind.

P4.4 Pressure Changes 1 Relate the change in volume of a gas to change in pressure applied to the gas at constant temperature and use the equation: pV = constant at constant temperature.

pV=nRT is definitely an equation you should try to learn. We call this the ideal gas law although we don’t need certain parts of the equation here.

Firstly, R is a constant with a value of approximately 8.31 but that is quite irrelevant for GCSE standards.

Basically, as you increase the Volume of a gas, the pressure of the gas sample decreases.

I will first try to explain this both quantitatively and qualitatively.

Quantitatively

pV= c, where c is a constant.

V = c/p

This is the rearrangment of what we call “Boyle’s Law”, and notice that Pressure is inversely proportation to Volume. Basically what that means is that as Volume increases, the pressure tends to decrease.

Alternatively, you can rearrange the original equation to arrive at:

p=c/V

Basically, here as pressure increases, volume decreases at a proportional rate.

The qualitative description can be seen through the diagram above. As you increase the volume, the particles in the container will have a larger volume to collide against, so therefore the overall concentration

of the collisions will decrease as each particle hence decreasing the overall pressure.

I’ll give you an analogy. If you’re in a small room and were forced to constantly walk around in circles, you will obviously hit the wall more often than if I put you in a larger room. What happens here is the frequency of the collisions increases as you decrease volume, hence increasing pressure.

P5.1 Thermal expansion of solids, liquids and gases 1 Describe qualitatively the thermal expansion of solids, liquids and gases.

Solids:

When thermal/heat energy is applied to a solid, the molecules of the solid gain kinetic energy and begin to vibrate more vigorously.

As a result, the solid expands slightly in all directions.

Liquids:

When a liquid is heated, the volume of the liquid increases as a result of the molecules having more kinetic energy. The liquid expands to take more of the volume of its container.

Gas:

The thermal expansion of a gas is slightly trickier depending on the situation:

If the gas is kept in a container of a constant volume, like a canister, and is then heated up, the gas does not expand. This is because gases take up the entire volume of its container. Instead, the pressure inside the container increases since the molecules have more kinetic energy and therefore collide with the walls of the

container more often.

On the other hand, if the gas is kept at a constant pressure inside its container, as the gas expands when heat is applied, the volume of the container will increase proportionally to the change in temperature.

2 Explain in terms of motion and arrangement of molecules the relative order of magnitude of the expansion of solids, liquids and gases.

Expansion of a substance: gas > liquid > solid

When a fixed mass of a substance is heated up, it will expand the most as a gas followed by as a liquid and lastly as a solid.

This is because the molecules in a gas have very weak intermolecular forces that keep them together as compared to the other two states of matter.

If we look at a solid, the intermolecular forces that keep it together are much more stronger. The molecules in a solid are arranged in a organized manner.

3 Identify and explain some of the everyday applications and consequences of thermal expansion.

Solids:

• Thermal expansion could be used to fit metal axles onto wheels. The metal axle is first cooled so that it contracts. It is then placed through the hole of wheel so that when it warms up and expands, it forms a tight grip on the wheel.

• Train tracks are built with gaps between each section of the track so that when it expands under hot weather, the train tracks won’t warp as a result of the pressure of being squished together.

4 Describe qualitatively the effect of a change of temperature on the volume of a gas at constant pressure.

Equation that links pressure, volume and temperature for a fixed mass of gas:

(P1*V1) / T1 = (P2*V2) / T2

In essence, the pressure and volume of a fixed mass of gas is proportional to its temperature in Kelvin

However, if P is kept constant, then our equation becomes:

V1 / T1 = V2 / T2

Where the volume of the gas is directly proportional to its temperature in Kelvin.

This is known as Charles’ Law.

P5.2 Thermal Capacity 1 Demonstrate understanding of the term thermal capacity

Thermal Capacity is often defined to be the amount of thermal energy required to raise the temperature of a substance by 1 Kelvin.

Obviously, different substances have different thermal capacities.

2 Describe an experiment to measure the specific heat capacity of a substance.

The formula for Specific heat capacity is :

E = m x c x ΔT we can rearrange the equation to get

c=E/ m x ΔT We want to find the Specific Heat capacity of water, which we know to be around 4200Jg-1°C-1

Steps

• Set up a circuit with a heater, voltmeter, ammeter, and variable power supply.

• Measure a quantity of water that you are going to use and weigh to get the mass

• Measure the amount of energy required to raise temperature of water by a certain amount of degrees using the circuit.

• Do the appropriate calculations. Please Note: Energy efficiency here is 100%. Sources: http://www.saburchill.com/physics/practicals/adobe/HG1a.pdf

3 Recall and use the equation for Specific Heat Capacity

c=E/ m x ΔT and this can be re-arranged to give:

E = m x c x ΔT Units in Joules.

P5.3. Melting and Boiling 1 Describe melting and boiling in terms of energy input without a change in temperature

There are two types of energy in a substance, which we often call to be the internal energy. The two types of energy are potential and

kinetic energy.

The kinetic energy is what defines the temperature of the substance. When the temperature of a substance reaches a state where it is ready to go through boiling/melting, energy is still being transferred but the temperature is still constant.

In this process, bonds are being broken/formed, so energy transfer is definitely required for this change in state. However, if the kinetic energy doesn’t change here, what changes? The potential energy increases.

2 Distinguish between boiling and evaporation.

One difference between boiling and evaporation is that evaporation happens at the surface of a liquid where boiling occurs inside the body of the liquid.

Additionally, evaporation can literally happen at any temperature, as long there is enough Kinetic Energy to break bonds, but boiling can only happen at certain temperatures, e.g. 100°C for water.

3 Describe condensation and solidification.

Condensation: This is the change of the physical state of matter from a gas into a liquid.

Basically, condensation starts by the formation of atomic clusters of the substance in its gaseous (gas) state, like the formation of a rain drop in the clouds.

Solidification: This is the change of the physical state of matter from a liquid to a solid.

A good example is changing water into ice cubes. You put the water into the fridge, and it freezes to become ice.

4 Use the terms latent heat of vaporisation and latent heat of fusion and give a molecular interpretation of latent heat.

Latent Heat of Vaporisation: The change of phase from liquid to

gas

Latent heat of fusion: The change of phase from solid to liquid.

Latent Heat: Amount of energy associated with phase change.

The molecules in a liquid are nicely packed together, not as packed as the solids, but packed enough so they don’t have complete freedom as in where to move around. However, if you apply some “energy” into the liquid, the molecules inside (internal energy) starts to become more energetic and move around more often. As you heat it for a longer period of time, some of its molecules will have enough energy to overcome the forces of attraction holding the liquid together, hence evaporating and changing phase to a gas.

The concept is similar in the change of phase from solid to liquid. Let’s say you have an ice cube. As we all know, the particles in the solid have little freedom to move around and can only vibrate around a fixed position. If you heat the ice cube, the particles will vibrate more rapidly, and as you heat it for a longer period of time, naturally, some of the molecules in the ice cube will have enough energy to overcome the forces of attraction holding the solid together, hence melting into a liquid. Obviously, this doesn’t happen all at once, its a gradual process where more and more molecules have enough energy to overcome the forces of attraction between molecules.

P6.1 Conduction 1 Describe experiments to demonstrate the properties of good and bad conductors of heat.

A simple experiment can be conducted to find out whether something is a good or bad conductor of heat!

Prepare a few rods made from different materials. Use wax to attach small pins to their ends and then heat the other end of the rods. The thermal energy will be transferred by conduction, from one end to the other. Eventually the wax will melt (due to the heat from the rod) and the pin falls off. The best conducting rod will have its pin dropped off fastest because it transfers the thermal energy the fastest!

2 Explain heat transfer in solids in terms of molecular motion.

• Conduction is a type of thermal energy transfer that occurs mainly in solids.

• In any solid object/substance, its particles are fixed in regular structure and they cannot move.

• However, when the solid object is heated, its particles gain thermal and kinetic energy. But since they cannot move, they vibrate instead.

• As particles with more kinetic energy vibrate, they also pass on the vibration to other particles too.

• Consequently, the thermal energy is also passed on! The right of the solid object is heated. The particles begin to vibrate. The vibration is passed on to the particles on the left. The thermal energy is also transferred when the vibrations are passed on.

P6.2 Convection 1 Recognise convection as the main method of heat transfer in fluids.

Fluids are often very poor conductors, but if they are free to circulate

they can carry thermal energy through a process called Convection.

2 Relate convection in fluids to density changes.

Credit:Eyrian

Above is an example of a convection current. If the bottom is gently heated, as the water above the flame becomes warmer, it expands and decreases in density. The less dense water rises as cooler, denser water sinks and takes its place, or we can say, Displaces it. This is a convection current.

However, convection does not occur if the water is heated at the top as warmer, less dense water will simply just stay at the top.

3 Describe experiments to illustrate convection in liquids and gases.

Convection in Air

Convection doesn’t only occur in liquids, they can also occur in gases. An example is the Convection Current in air.

Heated by the sun, the warm air rises above the equator and cool air displaces the warm air. This results in a convection current in the earths atmosphere.

Room Heating

Warm air rises above the heater or radiator, and it is displaced by

cool air.

P6.3 Radiation 1 Recognise radiation as the method of heat transfer that does not require a medium to travel through.

Radiation (unlike conduction and convection) does not require a medium to travel through. This means they can travel through anything and even empty space (vaccum). The best example would be radiation from Sun. Earth receives heat from the sun through radiation. The heat is transferred through Space (which we know is a huge vacuum) by radiation!

2 Describe experiments to show the properties of good and bad emitters and good and bad absorbers of infra-red radiation.

Dark or black surfaces tend to be good emitters and absorbers of heat

White or light-coloured surfaces tend to be poor emitters and absorbers of heat. Reflective surfaces will reflect the radiation and heat.

An easy experiment can be set up to see if a material is a good or poor emitter/absorber.

• Place different materials of different colour under the sun, or close to a source heat radiation.

• After a period of time, measure their temperature. The dark surfaces should be warmer because they are better absorbers of infra-red radiation.

3 Identify infra-red radiation as the part of the electromagnetic spectrum often involved in heat transfer by radiation.

• Radiation is a type of thermal energy transfer due to Electro-magnetic waves.

All hot object emit radiation

• Infra-red radiation is the most common type of heat transfer by radiation. Infra-red waves are a type of electro-magnetic waves and they are part of the electro-magnetic spectrum.

• It does not matter if you do not know what electro-magnetic waves and spectrum mean! You will learn about them later. Basically they are invisible waves that transfer energy.

P6.4 Consequences of Energy Transfer 1 Identify and explain some of the everyday applications and consequences of conduction, convection and radiation.

Conduction, convection and radiation are constantly happening in our every-day environment. They have many applications and can be very useful, some examples include:

• When we heat up pots and pans, the thermal energy is transferred through conduction

• Air condition uses convectional currents to cool the indoor environment.

• When heating up water, the heat is applied from below so it creates a convectional current, which heats up the whole body water

• Sea breezes are caused by convectional currents. This is due to the difference between the temperature of the sea and land.

• Radiation enters greenhouses through the glass and the heat is absorbed and trapped to maintain the temperature

Solar panels produce electricity by absorbing the heat from sunlight by radiation

P7.1 General Wave Properties 1 Demonstrate understanding that wave motion transfers energy without transferring matter in the direction of wave travel.

The statement is what it says above. However, I want to clarify some things in terms of how a wave motion can transfer energy without actually transferring any matter.

Consider the following example. You’re friend is on a swing. Let’s just assume that you’re friend is incompetent and you have to push him. You push him, but you don’t have to fly off with him, your mass can stay where it originally belonged (on the floor). You simply have to transfer the kinetic energy from your muscles (I assume you’re pushing your friend with your hand), to his swing. Basically, you’re pushing his mass with a bit of yours, which allows the swing to have enough energy to elevate the swing , but you don’t have to physically fly off as well.

Long story short, wave motion transfers energy, however the matter does not have to be transferred.

2 Describe what is meant by wave motion as illustrated by vibration in ropes and springs and by experiments using water waves.

Wave motion is the transfer of energy from one point to another.

E.g.

• Vibration in ropes: Particles in rope vibrate in a fixed position and energy in the particles are transferred from one end of the rope to the other end. Wave travels as a “sideway pulse”

• Water ripples: An object that is floating experiences both “up and

down” motions. 3 State the meaning of and use the terms speed, frequency, wavelength and amplitude.

Amplitude

The maximum displacement a point moves from its rest position when the wave passes. Since this is displacement, we usually give amplitude the same units as we would for distance/displacement. E.g. metre, kilometre

Frequency

The number of waves passing any given point each second, measured in Hertz (Hz).

Waves of different frequencies.

Wavelength (λ)

The distance over which the wave shape repeats -(http://en.wikipedia.org/wiki/Wavelength). Measured in metres, kilometres etc.

Example below:

CC Attribution: http://en.wikipedia.org/wiki/File:Sine_wavelength.svg

Speed:

Speed at which a wavefront passes through a medium, relative to the speed of light. (http://en.wikipedia.org/wiki/Wave_propagation_speed)

4 Recall and use the equation v = f λ

Velocity (m/s) = Frequency (Hz) x Wavelength (m)

In GCSE, the most complicated problems involving this equation are those that ask you to rearrange the equation.

5 Distinguish between transverse and longitudinal waves and give suitable examples

There are ultimately two types of waves:

Transverse Waves:

Wave oscillation is perpendicular to direction of energy propogation

Examples include:

• Seismic S waves • Light rays • Electromagnetic waves Longitudinal waves

Wave oscillation is parallel to direction of energy propogation

Examples include:

• Seismic P waves • Sound waves. 6 Identify how a wave can be reflected off a plane barrier and can change direction as its speed changes.

http://en.wikibooks.org/wiki/File:Introductory_Physics_fig_3.1.png

Reflection: If a wave hits a mirror plane, and the plane is nice and smooth, the wave will be directly bounced off and reflected.

http://en.wikibooks.org/wiki/Waves/Reflection_and_Refraction

Refraction: If the surface of the mirror/medium has interference and is not completely smooth, the wave is partially reflected but most of the wave will be refracted instead. Refraction means that the wave passes through the interface, and in the process acquiring a different direction from the trajectory of the wave that first hit the interface/medium.

During refraction, because the wave travels through a medium, naturally, its speed will also decrease. Most electromagnetic waves travel through the medium at the speed of light, but when they are refracted, they travel at a slower speed.

P8.2 Refraction of light 1 Describe an experimental demonstration of the refraction of light.

The phenomenon of the refraction of light can be observed when you shine beam of light through a transparent medium like glass or water.

In the above image, the image of the submerged pencil appears to be bent at an angle.

This is because when the light that allows us to see the pencil reaches the surface of the water, the angle of the light bends.

This is known as Refraction, and it is the bending of light waves as it passes from one medium to another medium with a different density.

2 Describe, using ray diagrams, the passage of light through parallel-sided transparent material, indicating the angle of incidence i and angle of refraction r.

Diagram of refraction of a ray of light as it goes from air to glass:

When light travels from a less dense material to a more dense material e.g. like from air to glass, the direction of the light bends towards the normal, which is 90o from the boundary.

Angle of incidence > Angle of Refraction when light travels from a less dense material to a more dense material.

Likewise, the opposite occurs when light travels from a dense medium to a less dense medium.

3 Describe the action of optical fibres and their use in medicine and communications technology.

Optical fibers are essentially cables made from high-quality glass.

When light enters one end of an optical fiber cable, it undergoes total internal reflection until it reaches the end of the cable.

Significant amounts of information can be transmitted at high speeds since digital information can be converted to visible light or infrared signal and be sent across optical fiber cables.

The advantages of using optical fiber over the traditional copper cable for sending information is that signals carried by the optical fiber do not weaken over long distances as compared to the copper cable. There is the fact that optical fiber cables can carry a larger quantity of information.

4 State the meaning of critical angle.

The critical angle is when the angle of incidence is such that total internal reflection is achieved. Light will be completely reflected if the angle of incidence is greater than the critical angle.

5 Identify and describe internal and total internal reflection using ray diagrams.

This diagram shows both internal reflection and total internal reflection.

When the Angle of Incidence (Ɵi) is less than the Critical Angle (Ɵc), both refraction and reflection is achieved. Only some of the light is reflected inside. As the angle of incidence gets closer to the critical angle, a greater of amount of light is reflected internally.

When the Angle of Incidence (Ɵi) is equal to or more than the Critical Angle (Ɵc), total internal reflection is achieved and the ray of light is completely internally reflected.

P8.4 Dispersion of Light 1 Describe the dispersion of light by a glass prism.

When light enters a different medium, the change in wavelength and speed depends slightly on the frequency. The higher the frequency, the higher the change in speed. We call this effect dispersion.

Take for example, when white light passes from air to glass, the highest frequencies (violet), are refracted the most as compared to the lower frequencies such as Red. This can clearly be seen in the diagram above.

In a shape like a triangular prism as shown above, the result of the refractions is a white light being spread into a spectrum.

P9. Electromagnetic Spectrum 1 Describe the main features of the electromagnetic spectrum.

2 State the approximate value of the speed of all electromagnetic waves in vacuo.

The Electromagnetic Spectrum is the entire range of frequencies electromagnetic waves can have.

All Electromagnetic waves have these certain characteristics:

They can travel in a vacuum. They travel at the speed of light in a vacuum – 3 x 108 ms-1 They are transverse waves. Since EM waves are transverse waves, they have multiple components that we can use to describe them.

We can describe EM waves using:

Frequency Wavelength Energy Frequency

The frequency of a wave can be defined as the number of peaks (or cycles) that pass through a certain point in one second. So a wave with one cycle per second would have a frequency of a single Hertz (Hz). A wave with two cycles passing through a given point in one second would have a frequency of 2 Hz.

Wavelength

The wavelength of a wave can be defined as the distance between the peaks of a wave.

The frequency and wavelength of a wave are inversely proportional to each other. If the wavelength of a wave decreases, we can expect the frequency to increase. It makes sense if you think about it. By having a shorter wavelength, more cycles are able to pass a given point within a second.

Energy

Lastly, we can describe an electromagnetic wave by the amount of energy it has, in form of a unit of measurement called electron volts (eV). An electron volt is the amount of kinetic energy needed to move a single electron through one volt potential.

In regards to the spectrum, as the wavelength shortens, the energy increases, making them inversely proportional to each other as well. A wave requires more energy to produce more waves within a given time.

3 Describe the role of electromagnetic wave in:

• radio and television communications (radio waves), • satellite television and telephones (microwaves), • electrical appliances, remote controllers for televisions and intruder

alarms (infrared), • medicine and security (X-rays). Types of Waves

Electromagnetic Waves can generally by classified into these seven types:

Radio waves Microwaves Infra-red (IR) Visible light Ultraviolet (UV)

X-rays Gamma rays Radio waves

The first type of wave observed by Heinrich Hertz, radio waves are often used for AM/FM Radio transmissions as well as TV broadcasting. Radio waves are produced as a result of accelerating electrons within a circuit.

Microwaves

Microwaves are used extensively in communications as well. Radar allows ships and planes to detect remote objects using microwave radiation. Many forms of wireless also rely on microwaves to communicate between one and another, although not at a level which can cause thermal heating. Lastly, microwaves are used in the aptly named microwave oven to heat food.

Infra-red (IR)

Infrared waves is commonly associated with thermal radiation. A vast majority of hot objects emit IR radiation, including ourselves, hot pieces of coal, heaters, and the sun. Hence, modern military and security often employ equipment capable of detecting IR radiation (Thermal goggles etc.) as a means to spot humans within a difficult to see environment.

Visible Light

Occupying a small window in the electromagnetic spectrum is the all-important visible light. The human eye is capable of detecting this part of the spectrum and it gives us an image of our surroundings. Thankfully, light comes in seven main flavours, giving life as we know it colour.

Wavelength Range /nm Frequency /THz Colour

390 – 455 659 – 769 Violet

455 – 492 610 – 659 Blue

492 – 577 520 – 610 Green

577 – 597 503 – 520 Yellow

597 – 622 482 – 503 Orange

622 – 780 384 – 482 Red

Ultraviolet Waves (UV)

Ultraviolet waves are very energetic and can actually ionize air, thus forming a part of the upper atmosphere known as the ionosphere. Harmful UV radiation given off from the sun is largely absorbed by ozone in the atmosphere. Still, not all of it is blocked and prolonged exposure to UV radiation can lead to conditions such as skin cancer.

X-rays

The largest source of x-rays on earth happens to be the natural environment and outer space. X-rays are also produced in x-ray tubes by firing electrons at a high velocity and having them rapidly decelerate as they collide with a metal anode (usually tungsten), giving off x-rays in the process.

X-rays are very penetrating and thus have important uses, especially in the field of medicine. First and foremost, x-rays are used in x-ray machines to provide images of our body’s internals without the need for surgery. In addition, they are used for radiotherapy and the management of cancer.

Gamma rays

Gamma rays are the most energetic, thus penetrating, waves of the electromagnetic spectrum. On earth, they are produced as a result of radioactive decay of an atom’s nucleus. The remaining source of gamma radiation comes from astrophysical sources such as pulsars, magnetars and quasars in space, giving off gamma radiation that then travel to earth.

As with all ionising radiation, gamma rays can have severe health effects. Long-term exposure can lead to increased incidences of cancer. However, despite their cancer-causing properties, they still are used in medicine for the purpose of radiotherapy, which involves killing cancer cells with focused beams of gamma radiation. In addition, gamma radiation can be used to sterilize equipment and food before it is used/consumed by killing bacteria through irradiation.

4. Demonstrate understanding of safety issues regarding the use of microwaves and X-rays.

The higher the frequency of the wave, the more energy it carries as it travels.

When a wave hits an object, the energy it carries is transferred to the object as kinetic energy. This is why when we microwave water, it gets warmer. The kinetic energy transferred is making the particles of the water vibrate faster, hence its temperature increases. This is the same with humans. If we are exposed to microwaves for a long period of time, there is the danger that permanent damage will be caused to our internal organs as they will warm up when the waves travel through our body.

Since higher frequency waves carry more energy, x-rays are more penetrating than microwaves. They can easily penetrate through most material including our bodies. Brief expose to x-rays carry the increased risk of cancer, since x-rays are ionizing. There is a potential that x-rays may cause mutations in living cells when they pass through the body, hence it is a very good idea that you limit your exposure to x-rays

P10.1 Sound 1. Describe the production of sound from vibrating sources. Sound travels through a wave: that is, a periodic disturbance in space and time. Mechanical vibrations (oscillation pf particles) cause a periodic disturbance in space and time, producing a wave.

2. Describe the transmission of sound in air in terms of compressions and rarefactions • Vibrations from the source of the sound compress the air, giving it

kinetic energy. The KE in the air particles cause them to move from its equilibrium position, exerting a force on adjacent air particles. The vibrations propagate through a series of perfectly elastic collisions.

• This is why sound is a form of energy. (E=hf) • After KE is transfered, the original particles experience a resultant

force (cf. Newton’s 3rd law) and move back to its equilibrium position. This creates a rarefraction in the wave.

• These Compressions and Rarefractions comprise of the sound wave. When it reaches the ear, the vibrations of the air particles are translated into sound.

Credits: http://labspace.open.ac.uk/mod/resource/view.php?id=443029

These compressions are a periodic disturbance (oscillation) that travels parallel to the direction of the wave. (longitudinal wave)

The pitch depends on how fast the particles vibrate, and therefore how often a cycle of compression-rarefraction happens (frequency) 3. State the approximate human range of audible frequencies

• 20Hz to 20,000 Hz • Remember this as 20-20: 20 Hz to 20 kHz 4. Demonstrate understanding that a medium is needed to transmit sound waves From the above explaination of sound waves: A sound wave is really a bunch of oscillating air particles (particles of any other medium). When there are no particles to vibrate, there is no sound wave.

5. Describe and interpret an experiment to determine the speed of sound in air http://www.instructables.com/id/How-to-measure-the-speed-of-sound-with-two-lumps-o/ • Stand a measured distance from a wall, x. • Make a short, loud burst of sound, start timing. • When you hear the echo, stop timing. let the value obtained be x. • The sound wave has traveled 2x. • Since v =ds/dt • substituting values • v = 2x/t = ~330 ms^-1 Interpretation: • rearrange the equation. In the form y=mx+c • ds = vdt • y = mx+c • If s is the independent variable and t is the dependent, plotting a

linear graph, v will be the gradient. 6. State the order of magnitude of the speed of sound in air, liquids and solids • Solids – Fastest • Liquids – Middle • Gases – Slowest Explaination: in terms of the atomic theory of matter, solids are the densest and gases are the least dense of the 3 states. Since sound travels by oscillating atoms (propagated through collisions), the denser the medium, the faster the speed.

7. Relate the loudness and pitch of sound waves to amplitude and frequency • Amplitude: the maximum extent of a vibration or oscillation,

measured from equilibrium. The higher the value, the more kinetic energy in the atom, which causes higher pressure in the medium, which translates to loudness when it reaches the ear.

• Frequency: the number of occurances of a repeating event per unit time (e.g. 1 compression and 1 rarefraction). For a given wave, all particles in the medium vibrate in the same frequency. Since these vibrations cause pressure in the medium, the higher the frequency, the faster the pressure fluctuation. The human ear detects these fluctuations as pitch.

8. Describe how the reflection of sound may produce an echo. When a sound wave is reflected, it has the same magnitude and different direction (sometimes moving back to the source). Since the wavelength and frequency is still the same, the observer perceives this as the same sound as the original. This is an echo.

P11.1 Magnetism For this unit, you’ll need to:

1. Describe the properties of magnets

“A magnet is a material or object that produces a dipole magnetic field (i.e. one with 2 poles), which pulls on other ferromagnetic materials and repels other magnets”

- has 2 poles, N->S

- Field movement from N->S

- Can be create with an induced electric current

Types of magnetic materials: Ferromagnetic (ferrous metals e.g. steel, iron – strongly attracted); Paramagnetic (e.g. Pt, Al, O2 – weakly

attracted to magnets); Dimagnetic (e.g. plastic, wood, copper – repelled by both poles; non-magnetic)

2. Give an account of induced magnetism. (Electromagnetic Induction)

1. By moving a wire up and down inside a magnetic field, it intersects the field perpendicularly, thus generating a current that is registered in the galvanometer. When the wire is moved in the opposite direction (e.g. up instead of down), the current flows the other way, creating an Alternating Current.

2. By moving a magnet inside a solenoid, the same effect is achieved (field and wire still intersect perpendicularly). In this case, it is the field moving and not the wire.

- The speed of movement affects the magnitude of the current.

- Direction of movement affects the dir. of current

- Amo. of coils in solenoid affects the magnitude of the current.

3. Identify the pattern of field lines round a bar magnet

- The direction of field movement is always North -> South

- 4. Distinguish

between the magnetic properties of iron and steel.

- There are 2 types of iron: Soft Iron and Hard Iron. (Describes Magnetic properties [Coercivity]. If you were hit on the head with a soft iron bar, it would still feel very hard).

- Soft iron is easy to magnetize, but does not retain its magnetism in the absence of a magnetic field. (The field aligns the electrons in the iron, grouping different particle spins together). Soft Iron has high susceptibility and low retentivity. This makes soft iron ideal for applications where the magnetic field can be turned on and off, e.g. as the core of an electromagnet.

- Hard Iron and Steel retains its magnetism in the absence of a magnetic field. However, unlike Hard Iron, Steel is harder to magnetize – therefore Hard Iron has high susceptibility and high retentivity, whereas Steel has low susceptibility and high retentivity

- The best magnetic materials are Ferrous (i.e. compounds of Iron). The reason why Iron is easier to magnetize than Steel is because it is 100% Fe, whereas Steel is a compound with a lower amo. of Iron than pure Iron.

5. Distinguish between the design and use of permanent magnets and electromagnets.

- Electromagnets are temporary: a result of the electric field (flow of electrons). When the pd. is removed, the magnetism goes away.

- Permanent magnets have their atoms aligned to produce a constant magnetic field.

- (Actually, the electrons are aligned according to spin [+-0.5] in each atom, and the proportion of +/- determines the poles. After a ferromagnetic material reaches a certain temp. [Curie Temperature], it becomes paramagnetic since the energy is transferred to the atoms, throwing them out of alignment. Purely for geeky fun, you don’t have to know this.)

- Use of Permanent magnets: Compasses, Apple’s MagSafe

chargers, fridge magnets, generators, dynamos, magnetic screwdrivers, door holders

- Use of Electromagnets: relays, speakers/microphones, motors, LHC, generators, dynamos, CRT, doorbells, electromagnets to pick up scrap metal in junkyards, Maglev trains, MRI

P12.1 Introduction to Electricity 1. Demonstrate understanding of current, potential difference, e.m.f. and resistance, and use with their appropriate units.

Electric Current:

• Is the flow of electric charge within a circuit. • Is measured in amperes or amps (A). • Represents how much electric charge is passing a single point in

the circuit in moment. • Does not run out in a circuit i.e. current is the same at the beginning

and end of a circuit. Potential Difference:

• Difference in potential between two points of a circuit. • Potential represents how much energy (joules per coulomb) there

is to drive a current through the wire and is measured in volts (v)

e.m.f:

• Electro-motive force (e.m.f) is the voltage (potential) that a battery will supply. It is the driving force that gives the electrons the energy to move around the circuit.

Resistance:

• Is a measure of how difficult it is to push a current through a circuit. • Is measured in Ohms (Ω) 2. State that charge is measured in coulombs (C)

Charge is a property that certain particles have that can have a force of repulsion or attraction (like electrons or ions).

The unit for electrical charge is Coulombs (C).

3.Use and describe the use of an ammeter and a voltmeter

Ammeter:

• Is a device used to measure the amount of current flowing through the circuit (in amps)

• Has to connected in series to the circuit

Voltmeter:

• Is a device used to measure the potential difference between two points in a circuit.

• Has to be connected in parallel to the component you want to measure.

P12.2: Electric Charge 1. Describe and interpret simple experiments to show the production and detection of electrostatic charges

Electrostatic Attraction can be reproduced and observed in a simple experiment:

• Get a balloon. • Inflate it. • Rub the balloon quickly on any dry surface e.g. a carpet.

• Go to the nearest faucet/ water tap. • Turn it on. • Place the balloon close to but not touching the running water. What do you notice?

You should see that the water bends towards the balloon.

2. State that there are positive and negative charges.

When two insulating materials are rubbed together (in this case a carpet and the balloon), the friction causes electrons on one material to be rubbed off and left stranded on the other.

Normally, objects are neutrally charged, meaning that the atoms have an equal number of protons and electrons. However, when we rub two insulating materials together, what we end up is one material is left too much electrons, and as result becomes negatively charged due to more electrons than protons.

Conversely, the other object is left with more protons than electron (loses it). Hence, it becomes positively charged.

Due to the nature of water molecules, they are polar, meaning that their molecules have a positive and negative charged ends, much like a magnet. They are very weakly attracted to charged objects.

3. Describe an electric field as a region in which an electric charge experiences a force.

An electric field is created when an electrically charged object is placed near another charged or polar object, creating a force of electrostatic attraction between the two.

In our experiment, the water bends towards the negatively charged balloon because:

• The positive pole of the water molecules are attracted to the negatively charged ions of the balloon. The positive pole of the water molecule aligns and rotates towards the balloon and is pulled towards it.

We also have to consider the fact that the water molecules have a negative pole as well, so shouldn’t it repel each other as well?

• The negative poles of the water molecule are repelled by the negatively charged ions of the balloon.

However, the water molecules still bend towards the stream. Much like a magnet, since the positive poles of the water molecules are closer to the balloon since they are attracted to it, the force of attraction between the positive ends is stronger than the repulsion between the negative ends.

4. State that unlike charges attract and that like charges repel

In essence, in the above experiment we can see that:

• Unlike (opposite) charges attract. ( + ) → ← ( – ) • Like (same) charges repel. ( – ) ← → ( – ) • A good analogy would be magnets. Think of magnets. 5 Distinguish between electrical conductors and insulators and give typical examples

Conductors are materials in which an electric current can flow freely. Examples include metals such as steel and copper. Metals have the property of being conductors of electric. They generally have a low resistance.

Conversely, insulators are materials in which an electric current cannot/will have a hard time flowing through. Examples include

materials such as wood, plastic, and glass. You should notice that electric circuits are never built entirely from these materials. They generally have a high resistance.

P12.3. Current, Electromotive forces and Potential Difference 1. State that current is related to the flow of charge

Current: is the flow of electrical charge within the circuit.

2. Demonstrate understanding that a current is a rate of flow of charge and recall and use the equation: I = Q/t

More specifically, current is the rate of flow of charge in a given point of a circuit, measured in ampere, or amp (A).

The general equation for working out current when you have steady flow of charge is:

I = Q/t

• I = Current measured in amps

• Q = the charge carried measured in coulombs • t = Time 1 Amp is equivalent to 1 coulomb of charge flowing through a fixed point per second.

Amps = coulombs / seconds

3. Use the term potential difference (p.d.) to describe what drives the current between two points in a circuit.

The potential in an electric circuit is a measure of how much joules per coulomb (Volts) there are in a specific point of a circuit.

To move an electric current through a metal wire, it takes work/energy. If you think about it, when you run electricity through a wire, it gets HOT. The electric potential energy carried by the current is used to push the current through the wire and the energy is lost as heat.

Therefore, potential represents how much energy there is to drive a current through the wire and is measured in volts (v).

The potential difference is the difference in potential between two points of a circuit.

It represents how much energy is given off when going through a specific point as it moves from a higher potential energy to a lower potential energy.

For example, if the potential difference of a light bulb is 3v, it means that 3 joules of electric potential energy that each of coulomb is being lost as heat and light energy as it moves through the light bulb.

In any electrical circuit, the potential at the end of the circuit is always 0 i.e. a potential of 0 volts.

4. Distinguish between the direction of flow of electrons and conventional current

Normally, in a electrical circuit, the flow of electrons go from (-) pole of the battery to the (+) pole.

However, the conventional current flows in the opposite direction of the flow of electron. This is because the battery provides an electro-motive force (e.m.f) that pushes the electrons forward, making them do work.

5.Demonstrate understanding that e.m.f. is defined in terms of energy supplied by a source in driving charge round a complete circuit

Electro-motive force (e.m.f) is the voltage (potential) that a battery will supply. It is the driving force that gives the electrons the energy to move around the circuit.

For example, a 12V battery will provide a e.m.f of 12V.

P12.4 Resistance 1.State that resistance = p.d. / current and understand qualitatively how changes in p.d. or resistance affect current.

Since resistance = potential difference / current:

↑ in Voltage = ↑ in resistance

↑ in Current = ↓ in resistance

2.Recall and use the equation R = V/I

When you need to calculate resistance, Ohm’s law states that:

R = V/I

Resistance (Ω) = Voltage (V) / Current (I)

For example, a light bulb has a potential resistance of 3 volts. If a current of 0.6 amps is flowing through the lightbulb, what is the resistance?

R = V/I

R = 3 / 0.6

Resistance = 5 Ω

3.Describe an experiment to determine resistance using a voltmeter and an ammeter.

A simple experiment can be performed to find out the resistance across an object:

Set up an ammeter somewhere in the series circuit: this will give you the amount of current flowing in the circuit.

Now, set up a voltmeter in parallel to the object, in this case a light bulb, to find the potential difference across it.

Using theequation R = V/I , we can find the resistance.

If the light bulb has a potential difference of 4V, and the circuit has a current of 2A, then the resistance is: 4/2 = 2 Ohms (Ω)

P12.5 Electrical Energy 1 .Recall and use the equations: P = I V and E = I V t.

Here are two equations you might need to know for the exam.

First one is:

P= IV (Unit: Watts)

P is power, I is Electric Current (measured in Amps), and V is Potential difference (Voltage, measured in Volts). Units for power is Watts. This is also known as Joule’s Law.

The second one is

E= I V t (Units: Joules)

E= Energy

I= Electric Current

t= time (sec)

P12.6 Dangers of electricity

1. Identify electrical hazards including: damaged insulation, overheating of cables, damp conditions

Damaged Insulation:

In a circuit, insulation is the plastic sheath that covers the wires. If you have damaged insulation, it means that the metal wires inside the cable are exposed.

The potential dangers of damaged insulation could be that if a person touches the exposed wire, they could be electrically shocked, which may lead to death.

Overheating of cables:

When you run a extremely high current through a cable, you run a risk of overheat the wire. This is because you are supplying too much energy and this causes to wire to heat up.

If the wires overheat, this could lead to electrical fires.

2. Demonstrate understanding of the use of circuit-breakers

A circuit breaker is a safety device that forces a circuit to open (switch off) when an extremely high level of current flows through the circuit.

Credit: Bidgee

Normally, electricity flows in the circuit breaker through the metal contacts.

However, if an extremely high current flows through the circuit breaker, the electromagnet get stronger and pulls the iron catch towards it.

This causes the spring to pull the metal contacts apart, causing the circuit to open/break.

In order to make electricity flow again, you simply press the reset button to push the iron contacts together.

3. Demonstrate understanding of the use of fuses

Fuses work in a similar way to circuit breakers. They are meant to protect the components in a circuit from overheating by breaking the circuit.

Fuses are integrated into the circuit they are meant to protect.

A high level of current flowing through the circuit causes the wires inside the circuit to heat up.

Inside the fuse is a metal wire with a low melting point. As a result of the running a high current through the circuit, the metal wire inside the fuse may melt. This causes the fuse and therefore the circuit to break.

Fuses can only be used once, since the wires inside them melt away.

P13.1 Circuit Diagrams 1. Draw and interpret circuit diagrams containing sources, switches, resistors (fixed and variable), lamps, ammeters voltmeters, and fuses.

2. Draw and interpret circuit diagrams containing magnetizing coils, transformers, bells and relays

Symbols:

Transformers

Coil

Bell

Relay

P13.2 Series and Parallel Circuits 1. Demonstrate understanding that the current at every point in a series circuit is the same

Current is the flow of electric charge within a circuit. Current does NOT ever change or run out in a series circuit. It is constant at ANY point in the circuit; it is the same at the beginning and at the end of a circuit.

2. Recall and use the fact that the sum of the p.d.s across the components in a series circuit is equal to the total p.d. across the supply

Since we know that all the potential energy is used up by the components in the circuit, the potential difference at the end of a circuit is always 0.

If the potential at the end of the circuit is 0, then we can say that the sum of potential difference across all components in a series circuit is equal to the e.m.f the supply provides or the potential difference across the supply.

3. Calculate the combined resistance of two or more resistors in series

For a series circuit, the total resistance is the equal to the sum of the resistance of each component:

RT = R1 + R2 + …

For example, if there are two resistors, each with 6Ω of resistance, then the total resistance will be:

6Ω + 6Ω = 12Ω

4. State that, for a parallel circuit, the current from the source is larger than the current in each branch

In a parallel circuit, the current in each ‘branch’ of the circuit is less than the current at the beginning or end.

Why?

In order to for electricity to flow through multiple branches in a parallel circuit, the current has to split up. This means that the current is weaker in each branch compared to the source. Imagine a river when it splits. The amount of water flowing in each river branch is less than the original, larger river.

5. Recall and use the fact that the current from the source is the sum of the currents in the separate branches of a parallel circuit

When circuit splits up into parallel so does the current. However, remember that the current at the beginning and at the end of the circuit is constant.

When the circuit rejoins again, the current at the before and after is the same.

Therefore, we can say that the sum of the currents in the separate channels of the circuit is equal to the current from the source.

6. State that the combined resistance of two resistors in parallel is less than that of either resistor by itself

It might seem illogical that when you add another branch to a circuit, that the total resistance of the resistance of the circuit decreases. You would expect it to remain the same

The best way to explain it would be by adding an additional branch to

the circuit, the total current flowing in the circuit increases. This is because the adding another branch gives the current another path which it could flow through.

Using the equation:

R = V/I

V (Voltage) remains the same since our power source does not change in a parallel circuit.

However, by adding more branches, our total current (I) increases in the circuit.

And if current increases, our R (Resistance) then therefore decreases.

7. Calculate the effective resistance of two resistors in parallel

Total Resistance in a parallel circuit is given by the equation:

1/RT = 1/R1 + 1/R2 + …

For example:

The total resistance of the circuit would be:

1/RT = ½ + ⅓ + ¼

1/RT = 6/12 + 4/12 + 3/12

1/RT = 13/12

RT = 12/13Ω or 0.92Ω

8. State the advantages of connecting lamps in parallel in a lighting circuit.

In a series circuit, connecting two lamps together results in decreased brightness for both of the lamps.

The lamps are not giving off light at their maximum brightness. This is because the electrical energy that the current carries is split between both lamps.

However, connecting two lamps in parallel results in both lamps outputting at maximum brightness.

This is because the energy carried by the current is not shared between the two lamps. The current split up and powers the lamp individually.

P14.1 Electromagnetic Induction 1. Describe an experiment that shows that a changing magnetic field can induce an e.m.f. in a circuit

The phenomenon of electromagnetic induction can be investigated through a simple experiment using a voltmeter, a coil of wire and a magnet:

CC Attribution: http://sub.allaboutcircuits.com/images/05071.png

Set up the apparatus like in the diagram above.

Now move the magnet through the coil of wire.

You should notice that a voltage is induced. When you move the magnet in one direction, you get a positive value for voltage. Likewise, when you move the magnet in the reverse direction, you get a negative value for voltage.

However, you should notice that no voltage is induced when the magnet remains still inside the coil. For voltage to be induced the magnet must be moving.

The induced voltage as a result of the magnet moving in and out of the coils of wire is called the Dynamo Effect. Voltage is generated whenever a wire is moved in a magnetic field. In addition, if it is in a complete circuit, then current will flow as well.

2. State the factors affecting the magnitude of an induced e.m.f

The magnitude of the induced voltage can be increased by changing several factors:

• The rate/speed in which the magnet moves • The strength of the magnet The number of coils that the wire makes – more coils means a bigger

voltage.

P14.2 A.C Generator 1. Describe a rotating-coil generator and the use of slip rings

A diagram of a rotating coil generator:

http://www.pbs.org/wgbh/amex/edison/sfeature/acdc_insideacgenerator.html

In a rotating coil generator, a current is induced whenever the coil of wire spins between the two magnets. However, every time the coil rotates 180o, the polarity and direction of the current alternates.

Fleming’s left hand rule:

Using Fleming’s left hand rule, we can understand why does the direction of the current induced alternate. In one half-turn, one end of the coil cuts through the magnetic field travelling upwards and then in the next half-turn, it cuts through the magnetic field downwards. Hence, as the coil is rotating in a magnetic field, the current generated alternates direction and polarity every 180o or half-turn.

The slip rings in an A.C generator provide an unbroken connection between the coil and circuit as it spins around, meaning that the current generated is always alternating. If another type, called a split-ring commutator is used instead, it will provide a D.C current

P14.3 Transformer 1. Describe the construction of a basic iron-cored transformer as used for voltage transformations.

Transformers are electrical components used to change the voltage supplied by an A.C generator.

Diagram of a step-up transformer:

A basic transformer will feature two coils of wire wrapped around an iron core like the diagram above. Depending on whether it is a step-up or step-down transformer, the number of turns (times the coil is wrapped around the core) for the primary and secondary coil will be different.

2. Recall and use the equation (Vp/ Vs) = (Np / Ns)

(Primary Voltage / Secondary Voltage) = (Turns on Primary / Turns on Secondary)

The equation states that the ration of voltage between the primary and secondary coil is the same as the ratio of the number of turns between the coils.

Basically:

• A step-down transformer has fewer turns on its secondary coil than its primary coil.

• Vice-versa, a step-up transformer has more turns on secondary coil than its primary coil.

Example question:

A transformer has 50 turns on its primary coil and 1000 turns on its secondary, what is the output voltage if the input voltage is 250 volts?

(Vp/ Vs) = (Np / Ns)

(250/Vs) = (50/1000)

250/Vs = 0.05

250/0.05 = Vs

Vs = 5000 Volts

3. Describe the use of the transformer in high-voltage transmission of electricity

One specific use of transformers is in the transmission of electricity over the National Power Grid at extremely high voltages.

One reason why transformers are used to transfer electricity at high voltages in things like the National Power Grid is because it is difficult to transmit electricity over long distances.

To transfer electricity over long distances at a given power, you either need a high voltage and low current or a low voltage and high current, since power is given by the equation: P=VI

However, the problem with transferring electricity at a high current is that you need a very wide cable to carry the huge amount of current flowing. This makes it more expensive that using a transformer to step-up the voltage, which in turn reduces the current flowing. With a low current, the wires can be thinner, making it more cost-beneficial for countries to use transformers to increase the voltage in their power grid.

In addition, once the electricity reaches its destination, transformers are used to step-down the high levels of voltage to make it much safer to use.

4. Recall and use the equation: Vp*Ip = Vs*Is (for 100% efficiency)

Primary Voltage * Primary current = Secondary Voltage * Secondary current

Or

Primary power supplied = Secondary power supplied

Using this equation, you can find out the power supplied by one side of the transformer if you know how much the other side supplies.

However, this only works if the circuit is 100% efficient, assuming that there is no energy lost somewhere along the circuit.

5. Explain why energy losses in cables are lower when the voltage is high

The amount of energy lost as heat when electricity is supplied is related to the amount of current flowing through the circuit.

When the electricity is being supplied, some of the energy carried is lost as heat to the wires due to the flow of electrons in the circuit. The larger the current flowing through the wires, the more energy is lost as heat to its surroundings.

When a generator supplies a certain amount of power, having a high voltage is beneficial since power is given by the equation P=VI. If we have a high voltage, then we have a small current, meaning that less energy is lost, making the generator more efficient at supplying energy.

P14.4 Magnetic Effect of a Current

B = magnetic field

I = current

The magnitude of the magnetic field generated by a straight wire carrying current is dependent on two factors:

• The strength of current. The stronger the current, the stronger the magnetic field is.

• The distance from the wire. The further you are from the center of

the wire, the weaker the magnetic field becomes. A solenoid is basically a wrapped coil of wire. The magnetic field it produces is similar to a bar magnet:

The strength of a magnetic field produced by a solenoid is dependent on 3 factors:

• The amount of turns that the coil makes. The more turns, the stronger the magnetic field.

• The strength of current flowing. The stronger the current, the stronger the magnetic field is.

• The radius of the coil. The smaller the radius, the stronger the magnetic field.

2. Describe the effect on the magnetic field of changing the magnitude and direction of the current

The strength of the current is proportional to the strength of the magnetic field. If one increases, so does the other.

When you change the direction of the current, the polarity of the magnetic field changes as well. So basically, the north and south pole of the magnetic field is reversed/swapped whenever you reverse the direction of the current.

3. Describe applications of the magnetic effect of current, including the action of a relay.

One way that the magnetic effects of a current are applied is in the use of the circuit breakers.

You know that the current flowing in a circuit is proportional to the

strength of the magnetic field it generates.

So in circuit breakers, when the current flowing gets too strong, the electromagnet becomes strong enough that it releases a latch, which in turns moves the contacts apart and opens the circuit.

In relays, an electromagnet is used to move the contact from one circuit to another. The strength and the direction of the current can be used to control the magnetic field the electromagnet generates which controls which circuit the contact is touching.

Diagram of a relay:

P14.5 Force on a current-carrying conductor 1 Describe and interpret an experiment to show that a force acts on a current-carrying conductor in a magnetic field, including the effect of reversing:

• the current • the direction of the field Whenever a current-carrying wire is placed into a magnetic field, a force/motion is generated and the wire moves. This is known as the Motor Effect.

A simple experiment to investigate the motor effect would be to place a wire connected to a power pack between two magnets. Then turn on the power. You should notice that the wire moves a tiny bit, due to the fact that the magnets may not be very strong.

The direction of the force generated/the wire moves depends on two factors:

• The direction of the current • The direction of the magnetic field In the above diagram, the wire moves downwards due to direction of the current and the magnetic field being set up that way.

If we change the direction of the current in the above diagram, then we get the opposite effect:

The wire moves upwards instead of down, due to the fact that the current is flowing in the opposite direction now.

Likewise, if we reverse the direction of the magnetic field:

The wire will move upwards instead.

2. State and use the relative directions of force, field and current.

We can deduce the direction in which the wire moves by using Fleming’s left-hand rule:

If you know what direction the current is flowing and what direction the magnetic field is aligned, then you can work out the direction in which the wire moves.

Simply align your fingers according to the direction of the magnetic field and the flow of current to find out the thrust of motion.

P14.6 D.C Motor 1 Describe the turning effect on a current carrying coil in a magnetic field.

2 Relate this turning effect to the action of an electric motor.

Remember when a current is carried by a wire through a magnetic field, it generates a force that either moves the wire up or down? This called the Motor Effect.

This principal can be applied to a coil inside a D.C motor as well:

Whenever a current passes through the coil, a turning effect is produced as one side of the coil moves upwards whilst the other side moves downwards (remember Fleming’s left-hand rule?) and the coil will spin.

However, there is a problem!

When the one part of the coil reaches the top, it will cease to turn. The force moving the coil upwards is balanced with force moving the coil downwards.

This is why you have the split-ring commutator at the end of the coil. The split-ring commutator reverses the current every half-turn to so that the force generated by the current keeps turning the coil in same direction.

3. Describe the effect of increasing: (a) the number of turns in the coil & (b) the current

a) Increasing the number of turns in the coil would increase the turning force generated, therefore the coil would spin faster.

b) Increasing the current flowing through the coil would increase the turning force generated, therefore the coil would spin faster.

P15.2 Detection of Radioactivity 1 Demonstrate understanding of background radiation

Background Radiation is the ionizing radiation that is constantly present in our natural surroundings.

Background radiation is usually either emitted from Natural (radon gas from earths crust) or Artificial Sources (Nuclear Power Plant accidents).

Background radiation can have severe consequences on health, as the radioactive particles may ionize and mutate ones DNA, causing diseases such as cancer.

2 Describe the detection of α-particles, β-particles and γ-rays

Geiger Muller Counter

• Tells us number of particles detected per minute

• GM tubes operate using the “ionizing” effect of radioactivity. This means they best detect alpha particles because Alpha Particles ionize most strongly.

Photographic Film • Scientists discovered that Uranium compounds would darken a

photographic plate, even if the plates were wrapped up so no light could penetrate it.

• Workers in the nuclear industry will wear “film badges”. These are sent to the labs each month to be developed. This allows scientists to measure the dose that each worker has received.

The badges also have “windows” made out of different materials, so we can see how much of the radiation was alpha, beta and gamma.

15.3 Radioactive Decay 1 State the meaning of radioactive decay.

Radioactive decay (nuclear fission) happens when unstable nuclei decay:

• During decay a small portion of the mass is lost and converted directly into large amounts of energy.

• This energy is harnessed in nuclear power stations to generate electricity, in atom bombs to create explosive power and in thermonuclear bombs to kick-start nuclear fusion.

2 Use equations (involving words or symbols) to represent changes in the composition of the nucleus when particles are emitted.

Alpha Decay

• Alpha radiation is released in the form of a helium atom. 238

92U –> 23490 U + 4

2 He

Just remember that the proton number on the left and on the right have to be balanced.

E.g. There are 92 protons in the nucleus of the Uranium atom, but when it goes through alpha decay, there are 90, but this is compensated by the two protons received from the helium atom.

The same applies for nucleon number on top.

238 = 234 + 4

Beta Decay

• Releases an electron

the Ve is actually an anti-neutrino, but don’t worry about this just yet. At GCSE, just learn to take a deep breath.

As usual, Proton numbers have to be balanced on each side, and so does the Nucleon Number.

Gamma Radiation

In gamma radiation, as it is an electromagnetic wave, energy is released instead.

P15.4 Half Life Calculation 1 Use the term half-life in simple calculations, including the use of information in tables or decay curves.

Concept

• Half life is the amount of time for half the atoms in a given sample to undergo radioactive decay.

• The symbol given for half life is T½ • Half-life varies from isotope to isotope How to calculate half life?

Nt = Nο x (0.5)^number of half lives

Nt= amount of radioisotope still remaining

No = amount of radioisotope originally there.

Here is some data:

NUMBER OF HALF-LIVES

TIME (YEARS

)

% STRONTIUM-

90 REMAINING

% STRONTIUM-90 THAT HAS

DECAYED 0 0 100 0 1 28 50 50 2 56 25 75 3 84 12.5 87.5 4 112 6.25 93.75 5 140 3.125 96.875 6 168 1.5625 98.4375

From here, we can see that we start off with 100% of Strontium-90. After 20 years, the number falls down to 50. Then after another 20 years, the number halves again. This continues and continues and continues, until the percentage slopes down to zero (or something very close to zero).

P15.5 Radiation: Safety Precautions You should be able to know:

1 Describe the hazards of ionising radiation to living things. 2 Describe how radioactive materials are handled, used and stored in a safe way to minimise the effects of these hazards.

P1 Describe the hazards of ionising radiation to living things.

Ionizing radiation isn’t good. Here are a few things they can do living things:

It removes electrons in your body which can mutate your DNA

This can cause Cancer, burns, and radiation sickness

P2 Describe how radioactive materials are handled, used and stored in a safe way to minimise the effects of these hazards.

P15.6. The Nuclear Atom -Isotopes 1 Use the term isotope.

Isotopes are atoms of the same element with the “same” number of protons but with different number of neutrons

2 Give and explain examples of practical applications of isotopes

14C is used for Carbon dating

In this process, the useful thing comes from the fact that living organisms take up carbon throughout their lives . The percentage of the isotope Carbon 14 is fairly constant in our atmosphere.

This means that the percentage of carbon 14 contained by all living organisms is also constant. However, when a living organism dies it stops taking up carbon 14. The isotope decays naturally with a half life of about 5,600 years. So a simple procedure involving counting the radioemissions due tocarbon 14 from a sample of material that was once alive, can be used to estimate its date.

Cobalt 60 is used in hospitals as a beta emission source in the treatment of cancer

• -Can be focused on Cancerous tissues to destroy them. • -Known as radiotherapy