P2 Topic 1 & 2

Proton Neutron Electron

Charge +1 0 -1

Mass 1 1 0.0005 (almost zero)

The charge and mass of electrons, protons and neutronsP2.1 Static Electricity

Protons = positively chargedElectrons = negatively charged.Electrons are in the shells of atoms. Charge of an atom = neutral as the + and the – are equal.

Static electricityIn insulator can become charged by friction through the transfer of electrons.

A substance that gains electrons becomes negatively charged, while a substance that loses electrons becomes positively charged.

When a charged object comes near to another object they will either attract or repel each other.

If the charges are the same - they repelIf the charges are opposite - they attract

P2.1 Electrostatic PhenomenaThe negatively charged balloon repels the electrons in the wall and they move away. The positive charge left behind attracts the balloon.

The negatively charged comb repels the electrons in the paper. The positive charge left behind is attracted to the comb which is why it picks up the paper.

P2.2 Uses and Dangers of staticHow lightning is caused:• Static electricity can build up in clouds. This can cause a huge spark to form between the

ground and the cloud.• A flow of charge through the atmosphere.Static is dangerous when:• There are inflammable gases or vapours or a high concentration of oxygen. A spark could

ignite the gases and cause an explosion.• You touch something with a large electric charge on it. The charge will flow through your

body causing an electric shock.

Static electricity builds up on everyday objects. It can be dangerous if it can create a spark. A conducting path can be used to prevent sparking.

Earthing removes excess charge by movement of electrons.

The electrons flow through the earthing cable to earth rather than there being a discharge and spark.

Paint Spraying

1) The car is negatively charged.2) The paint is positively charged. The positively charged paint spreads out as the repel each other.3) The negative attracted to the positive and stick.4) The metal spray nozzle is connected to the positive terminal of the power pack and the paint picks up a positive charge.

Air craft can build up a static charge when flying through the air and refuelling can also build a charge. To stop explosions the aircraft has a bonding line which is used to connect the air craft to the earth before it has been refuelled.

Insecticide spraysInsecticide use static electricity. Sprayed from aircraft so that they cover a large area. Risk that some of the spray will blow away or fall unevenly. To prevent this, the insecticide is given a static charge as it leaves the aircraft. The static drops spread evenly as they all have the same charge and are attracted to the earth.

P2.2 Uses and Dangers of static

P2.3 Electric CurrentsMaterials contain electrons. Insulating materials the electrons cannot move but in a metal they move and this can and this creates a current.

Be able to use the equation:

charge (coulomb, C) = current (ampere, A) x time (second, s)

Q = I x t

Key terms• Current is the flow of charge• Current in metals is the flow of electrons• Cells and batteries supply direct current

(d.c.)• Direct current is the movement of charge in

one direction.

Voltmeter Ammeter

Measures voltage in Volts

Measures current in Amps

Measures the energy difference between the electrons going into the component and back.

Electrons not used up out the output is the same as the input back to the cell.

Parallel Series

No junctions Current splits up at a junction

Potential difference measured.

Current size measured.

P2.4 Current and Voltage.

Potential difference is the energy transferred per unit charge.

1 Volt is 1 Joule per Coulomb

P2.6 Changing resistances

• Resistance measures how hard it is for the electricity to flow through a circuit.• Measured in Ohms• Dependant on how many components are in the circuit.• The higher the resistance the lower the current.• Variable resistor = can change the resistance of a wire.

Component Resistance

Filament lamp. As they get hot the resistance decreases. They get hot as they have a higher potential difference.

Diodes Electricity flows in one direction. If a potential difference is applied in the other direct no current will flow.

Light dependant resistor Resistance is high in the dark and low in the day time

Thermistor High resistance when cold, low resistance when hot.

Be able to use the equation:

potential difference (volt, V) = current (ampere, A) x resistance (ohm, Ω) V = I x R

P2.6 Changing Resistances

P2.7 Transferring energyEquations you must be able to use

Calculating Electrical Powerelectrical power (watt, W) = current (ampere, A) x potential difference (volt, V)

P = I x V Energy transferred (joule, J) = current (ampere, A) x potential difference (volt, V) x time (second, s)

E = I x V x t

Distinguish between the advantages and disadvantages of the heating effect of an electric current

Advantages Disadvantages

Useful Heating a kettle

Wasted energy

Useful in Fires Cause burns

A current in a wire is a flow of electrons . As the electrons move in a metal they collide with the ions in the lattice and transfer some energy to them.

This is why a resistor heats up when a current flows through.

P2 Topic 3

Force and Motion

Vectors and VelocityQuantities which have a direction and size are known as VECTOR QUANTITIES.

4 Examples• Displacement – distance travelled in a particular direction. • Velocity – speed in a particular direction.• Force – always has a size and direction.• Acceleration – it has size and direction

Speed (m/s) = distance (m) ÷ time (s)

Acceleration (m/s2) = change in velocity (m/s) ÷ time (s)

Key equations you need to be able to use:

Distance/Time Graphs• Horizontal lines mean the

object is stationary.• Straight sloping lines mean

the object is travelling at a constant speed.

• The steeper the slope, the faster the object is travelling.

• A curved line means acceleration.

• To work out the acceleration, you need to calculate the gradient.

Velocity/Time Graph• Horizontal lines mean the object

is travelling at a constant velocity.• Straight sloping lines mean the

object is accelerating or decelerating.

• The steeper the slope, the faster the acceleration.

• A curved line means acceleration. • The area under the graph is the

distance travelled.

ForcesA force is a push or a pull.When two bodies interact, the forces they exert on each other are equal in size and opposite in direction. These are known as REACTION FORCES.

You need to be able to interpret these diagrams and work out the resultant force in each direction.

If the resultant force is zero, it will remain at rest or continue to travel at a constant speed. If the resultant force is not zero, it will accelerate in the direction of the resultant force.

Forces and AccelerationThe size of acceleration depends on:• Size of the

force• Mass of the

object

Key equation you need to be able to use:

Force (N) = Mass (kg) x acceleration (m/s2)

In a vacuum • all falling bodies accelerate at the same rate.

In the atmosphere • Air resistance increases with increasing speed. • Air resistance will increase until it is equal in size to the weight of a falling object.• When the two forces are balanced, acceleration is zero and TERMINAL VELOCITY

is achieved.

Terminal Velocity

Key equation you need to be able to use:

Weight (N) = Mass (kg) x gravity (N/kg)

P2 Topic 3

Momentum, energy, work and power

Stopping DistancesStopping distance = thinking distance + breaking distance

6 Factors affecting stopping distance:1. Mass of vehicle2. Speed of vehicle3. Drivers reaction time4. State of the breaks5. State of the road6. Amount of friction between

the tyre and the road surface.

5 Factors affecting reaction time:1. Age of driver2. Drugs e.g. alcohol3. Visibility4. Tiredness5. Distractions

Investigating friction. How much force is needed to move weights on different surfaces?

MomentumA measure of motion. Mass multiplied by velocity.

When a moving object collides with another object, the momentum is the same before the collision as it is after the collision.

Momentum and SafetyWhen you are travelling in a car (or on a bike, skis, train etc.) you are travelling at the same speed as the car. If the car stops suddenly, your momentum continues to carry you forward. If you are stopped suddenly, by hitting the dashboard (or ground) you experience a large force, and therefore a large amount of damage.

Car safety features:

1. Seatbelts – stretch to increase the time taken to stop, thus reducing the rate of change of momentum and reducing injury

2. Air bags – inflate to increase the time taken to stop, thus reducing the rate of change of momentum and reducing injury

3. Crumple Zones – crumple and fold in a specific way to increase the time taken to stop, thus reducing the rate of change of momentum and reducing injury

Use this formula:

Force (N) = change in momentum ÷ time

If you increase the time you reduce the force.

Work and PowerKey definitions• Work – the amount of energy transferred. Measured in Joules (J)• Power – The rate of doing work. Measured in Watts (W). 1 joule per second is 1

watt.

Use this formula:

Work Done (J) = Force (N) x distance moved (m)

Example – if a 1kg mass (10N) is moved through a distance of 2 metres the work done is 20J.

Use this formula:

Power (W) = Work Done (J) ÷ Time taken (s)

Example – if a 24J of work is done over a 30 second period, the Power would be 24 ÷ 30 = 0.8W

Potential and Kinetic Energy

You need to be able to use these equations:

GPE = mghKE = ½mv2

Key Definitions• Kinetic Energy – movement energy• Gravitational Potential Energy – the energy something has due to its position relative to

Earth – i.e. its height.

Conservation of EnergyWhen energy is transferred, the total amount always remains the same.

P2

Topic 5 Nuclear Fission and Nuclear Fusion

P2.23 Isotopes

Keywords• Sub-atomic particles – a particle that is smaller than an atom• Nucleons – The subatomic particles in the nucleus of an atom e.g. protons and neutrons• Isotopes – Atoms of an element with the same number of protons and electrons but with a

different number of neutrons.

Remember• The Mass number is More that the

atomic number

Atoms• Atoms contain electrons, protons and neutrons = subatomic particles• Protons and Neutrons in the nucleus = they are called nucleons• All atoms on one element have same number of protons = atomic number• Mass number = number of protons and neutrons in the nucleus

Isotopes• Atoms with different number of neutron (same number of protons)• Different mass numbers• Examples

– Lithium – 6 and Lithium-7– Carbon-12 and Carbon-14

• An atom with a number attached referred to the isotope (as above)

Ionising radiation

Keywords• Unstable – an unstable nucleus is one that will decay and give out ionising radiation• Radioactive Decay – when an unstable nucleus changes by giving out ionising radiation

to become more stable• Ion - An atom with an electrical charge (through loss or gain of electrons)

P2.24 Ionising radiation

Alpha Beta Gamma

• Particles containing 2 protons and 2 neutrons (Helium atom nucleus)

• No electrons = 2+ charge• Emitted from nucleus at high

speed• Lose energy as they ionise an

atom• Produce many ions quickly so

have short penetration distance

• Stopped by a few cm of air of mm of paper

• Electrons that are emitted from an unstable nucleus

• Much less ionising that alpha

• Can penetrate much further into matter

• Stopped by a few mm or aluminium or even thinner lead.

• High-frequency electromagnetic waves emmited by unstable nuclei

• Travel at the speed of light

• Ten times less ionising that beta

• Penetrate matter easily• Stopped by a few cm of

lead or many metres of concrete.

P2.25 Nuclear reactions

Keywords• Nuclear fission– the splitting on a large nucleus.• Nuclear fusion – the joining of two small nuclei

Nuclear Fission• Nucleus splits into two smaller nuclei• Two or more neutrons also released• NOT the same as radioactive decay• If neutron are absorbed by other nuclei it can make them unstable – they then

split releasing more nuclei = chain reaction (like an atomic bomb.• Can be controlled with materials to absorb neutrons (like in a nuclear reactor)

Radioactive Decay• Releases energy• Alpha and Beta = kinetic energy• Gamma = energy in form of electromagnetic

radiation

Nuclear Fusion• Small nuclei can combine to

form larger ones• Also releases a lot of energy

P2.26 Nuclear power

Nuclear Reactors• Transform energy contained in nuclei of uranium and plutonium into thermal energy• Nuclear fission• Pellets of uranium inserted into hollow rods• Rods place in reactor core• Rate is kept constant but controlling the chain reaction• Number of free neutrons will not increase of decrease• Extra neutrons absorbed by control rods• Control rods placed in between fuel rods in reactor core• Control rods can be moved in and out to change the rate of fission• Fully lowered they shut down the reactor.

Keywords• Moderator – a substance in

a nuclear reactor which slows down neutrons so that they can be absorbed by the nuclear fuel more easily.

• Radioactive waste – Material left over after the fission of uranium that is radioactive

Generating electricity• Thermal energy from core is transferred to coolant

(usually water)• Coolant pumped through reactor• Coolant at high pressure pumped to heat exchanger to

produce steam• Steam drives turbine which turns generator• Generator transfers kinetic energy to electrical energy.

P2.27 Fusion – our future?

KeywordsPeer reviewed – work checked by different scientists working in the same fieldValidate – to confirm scientific theory is true

• Scientists investigating fusion to generate electricity• The helium produced is not radioactive• Materials used to contain fusion do become radioactiveGetting new ideas accepted• Scientific theories have to be validated• By the scientific community• Report and results are peer-reviewed• Other scientists must carry out the experiment and get the same results

Fusion and temperature• The nuclei that fuse are both positively charged so repel = electrostatic repulsion• Nuclei need to be extremely close• High density nuclei are more likely to collide e.g. in the Sun the high gravitational field creates high

density nuclei.• Difficult condition to create on earth• Fusion reactors try to produce high pressures and high temperature• High temperatures = more kinetic energy to overcome repulsion and collide.• These conditions require a lot of energy (more than the reactor can make so currently not very

efficient)

P2

Topic 6 Benefits and drawbacks of using radioactive materials

P2.28 Changing ideas

Henri Becquerel and Marie Curie• Accidental discovery was made that Uranium exposed photographic plates =

discovery of radioactivity• Showed how radiation could ionise gases• Skin burns visible from handling Radium• By 1920s links made with cancer (Marie Curie died of lukaemia)• Large amount of ionising radiation = tissue damage (radiation burns)• Smaller amounts regularly = DNA damage (mutations)• Some mutations lead to cancer

KeywordsHazards – causes of harmRisk – likelihood of harmMutation – a change in the base sequence of DNA.

Handling radioactive sources• Risk of harm decreases with distance from the source• Sources always handled with tongs• Risk reduced by not pointing sources at people• Keep sources in lead lined containers

P2.29 Nuclear Waste

High level waste • The fission products from Uranium fuel are very radioactive• Produces large amounts of ionising radiation for about 50

years• Remains moderately radioactive for thousands of years as

intermediate level waste• Transported in thick concrete and steel containers• Sealed in glass to prevent escape• Stored in canisters until it becomes ILW

Intermediate level waste• Remains moderately radioactive for

thousands of years • Includes the metal cylinders that contained

uranium fuel which become radioactive• Stored in concrete and steel containers• None disposed of yet

Low level Waste - • Only slightly radioactive• Remains so for tens of thousands of years• Clothing and cleaning materials from nuclear power

stations• Hospitals also a source of LLW from radiotherapy

cancer treatments • Compacted and buried in special landfill

Advantages of nuclear power Disadvantages of nuclear power

• Station does not produce CO2 • Less impact on global warming

• Making the fuel rods requires energy (CO2 released)• Waste has to be stored for tens of thousands of years without

leaks• People perceive it as unsafe after the Chernobyl accident

Disposal methods 1. Firing into space

– Risk of it falling back2. Dumping in barrels at sea

– Barrels can corrode– Enters food chain

3. Storage underground– Need geologically stable site– Low earthquake risk

P2.30 Half-life

Radioactive decay• Unstable nucleus undergoes radioactive

decay to become more stable• Activity of a substance is the number of

nuclear decays per second• Measure in becquerel (Bq)• 1Bq is one nuclear decay each second• Radioactive decay is a random process

(cannot predict it)• Half life = the time taken for half the

unstable nuclei in a sample of a radioactive isotope to decay.

• Half life does not change as the sample gets smaller

• After decaying = more stable nucleus• More stable nucleus = lower activity• Half life found by recording activity over a

period of time.

Geiger-Muller tube

• Used to measure radioactivity• Can be connected to a counter or may

give a click when radiation detected• Count rate = number of clicks per

second or minute

P2.32 Background radiationKeywords• Background radiation – ionising radiation that is around us all the time from a number of sources.

Some is naturally occurring.• Background count – the average number of counts recorded by a GM tube in a certain time from

background radiation• Radon gas – naturally occurring radioactive gas that is emitted from rocks as a result of the decay of

radioactive uranium

Background Radiation• Main source = radon gas• Released from decaying uranium in rocks• Diffuses into the air from rocks and soil• Medical sources = x-rays; gamma rays (scans) and cancer treatments• Some food are naturally radioactive• Cosmic rays = high energy charged particles from the stars (like the Sun) and supernovae,

neutron stars and black holes.• Many cosmic rays are stopped by the atmosphere but some reach Earth.

• We are constantly exposed to ionising radiation – from space and naturally occurring = background radiation

• Needs to be considered when measuring a source• Background count is subtracted from the source count

P2.33 and P2.34 Uses of radiation

Treatment of Cancer• Radiotherapy = ionising radiation to treat

cancer.• Gamma rays used as beams to target and kill

cancer cells.

Diagnosis of Cancer• Gamma rays used• A tracer solution injected into body that collects in

cancers• Gamma camera used to detect rays• Pass through the body so easily detected

Sterilisation of equipment• To kill microorganisms surgical

instruments need to be sterilised• Heat usually used but cannot be used

on some things e.g. plastics• They are irradiated with Gamma rays

instead.

Irradiating food• Bacteria will cause food to decay or make us ill• Gamma rays kill bacteria• Makes food safer and longer lasting• Does not make food radioactive• Foods like Fruit, cereals and shellfish are irradiated.

Smoke Alarms• Contains a source of alpha particles• There is an electrical circuit with a gap

between 2 charged plates.• Air in gap is constantly ionised therefore

constant electric current.• When smoke get in the alpha particles are

absorbed and stops the current drops = alarm sounds

Checking thickness• Use a detector to measure the rate

Beta passes through paper• Thinner paper = higher beta count.

Tracers in the environment• Added to water to monitor pollution or

leaking pipes underground• GM tube follows the pipe to detect leaks.