Physics Topic 3.1 Radiation in Medicine Keywords • Ionising Radiation – radiation that can cause charged

particles by knocking electrons from the atom. Causes tissue damage and may cause mutations.

• Intensity – the strength of a wave defined as power of incident radiation/area.

• Diagnosis – identifying a medical condition by its signs and symptoms or from a medical imaging scan

• Non-ionising radiation– radiation that does not cause formation of charged particles.

• Incident radiation– falling of striking of radiation on something.

Facts: • Intensity is an example of a compound

measure (its units are determined by the units used in the calculation)

• Standard units = W/m2

• Visible light - example of radiation (energy carried by waves from a source)

• Different types used to identify and treat medical problems.

• Produce images that show features inside the body.

• Non-ionising = lasers used in eye surgery; ultrasound to treat swelling.

• Intensity decreases with distance from source. (Different tumours treated with different intensities)

• Denser medium to move through = weaker radiation.

Visible light

Light reflects to form an image Endoscopes

X-ray Absorbed by some material but not others. Negative image produced

X-ray photography and CAT scanners

Gamma Rays Movement of a substance producing Gamma rays is detecting and observed

PET scanners

Ultrasound High frequency sounds waves reflect off internal features Ultrasound scanners

Intensity (I) = power of incident radiation in Watts (P) W/m2 area in Metres squared (A)

P3.2 – How eyes work

Eye structure diagram

• Constricted pupil – small to reduce light entering • Dilated pupil – larger to allow more light to enter Image formation • Light converges on the retina • Path of rays is changed by the eye by refraction (carried out by cornea and lens) • Ciliary muscles change the shape of the lens to keep image focussed on retina if the distance alters.

– Contracted ciliary muscles = loose ligament = lens more rounded = focus on nearby objects – Relaxed ciliary muscles = taut ligaments = lens flattened = focus on distant objects

• No limit to how far away you can focus – far point is at infinity • You near point is approx. 25cms – nearer and image is blurred.

Accommodation/ Focussing

1. Which medical techniques use harmful, ionising radiation?

2. What is ionising radiation? 3. What type of image do x-rays form? 4. What radiation is used in PET scans? 5. Give two examples of ionising radiation

using in medicine 6. State the equation for calculating the

intensity of radiation. 7. State 2 types of non-ionising radiation

used in medicine

P3.1 Radiation in Medicine

1. What are the main structures of the eye?

2. What controls the amount of light entering the eye?

P3.2 – How eyes work

3. Which medical techniques use harmful, ionising radiation?

4. What distance is your far point when focussing?

5. Why does an image get blurred when it is nearer that 25cm to your eye?

6. What is the job of the ciliary muscle

P3.3 –Sight problems

Keywords

• Short Sight– cannot focus on distant objects as light rays focus on a point in front of the retina • Long Sight – cannot focus on near objects as light rays focussed to a point behind the retina • Diverging Lenses – spreads out light rays • Converging Lenses – brings light rays together

Short and long sightedness • Near objects = lens is shorter and fatter • Distant object = lens is thinner

Short sighted • Eyeball too long or cornea curved too sharply • Rays focussing in front of retina • Distant objects are blurred

Long sighted • Eyeball too short or lens not thick /curved

enough. • Taut ciliary muscles still cannot bend the light

enough • Near objects are blurred

Correcting vision • Short sight corrected by glasses with diverging

lenses – Bends light apart to focus correctly on

retina • Long sight corrected by glasses with converging

lenses – Refracts the light more to meet on the

retina. Laser Correction

• Uses a laser beam to reshape the front of the cornea

• Lasers make precise incisions without damaging surrounding areas

• Changes the way light is refracted by the cornea

1. A person who is long sighted struggles to focus what objects?

2. What lens shape is needed to correct short sightedness?

3. What lens shape is needed to correct long sightedness?

4. State methods other than glasses that can be used to correct vision problems

5. How can you permanently correct a person’s vision? Explain how it works.

P3.3 –Sight problems

1. Where does the image focus in a person who is short sighted?

2. How does a converging lens change the path of a light ray?

3. What is the point at which converging rays meet called?

4. What are the main causes of short sightedness?

P3.3 –Sight problems

P3.5 Different lenses Keywords • Dioptres – Unit for measuring the power of a lens • Real Image – An image that can be projected onto a

screen • Virtual Image – An image that cannot be projected

onto a screen

Converging lens – parallel rays refracted and meet at focal point

Lens to focal point = focal length Diverging lens – focal point is point rays seem to coming from

Focal point to lens = focal length

Power of a lens = 1 (dioptre, D) Focal length(metre, m)

Lens Equation – links the object distance (u), the image distance (v) and the focal length (f) 1 = 1 + 1 f u v

Snell’s Law • Links the angles of incidence and

refraction when waves travel from one medium to another.

• The constant is related to the refractive index (n) of each material

Refraction • In a denser medium the waves travels

slower • Wave changes direction = refraction • If slowed down – refract towards the

normal • If travelling faster = refract away from

normal

P3.6 Refraction Refractive index = speed of light in air

speed of light in substance

image

actual location

normal

Angle of incidence

Angle of refraction

Sin i nr = Sin r ni

nr - refractive index of medium ray is travelling into ni - refractive index of medium ray is travelling from

1. Define the term focal length. 2. Where is the focal point in a diverging lens 3. How is the power of a lens measured? 4. What unit is used to measure the power of a

lens. 5. What is the lens equation 6. What factors are linked in the lens equation? 7. Define a ‘real image’. 8. Define a ‘virtual image’.

P3.5 Different lenses

1. What happens to the speed and direction of a light wave if it enters a denser medium?

2. When a ray passes into a material where is can move faster does it refract towards or away from the normal?

3. How do you calculate the refractive index of a substance?

4.In Snell’s law what to nr and ni stand for?

P3.6 Refraction

Incident angle ∠i

Reflected angle ∠r

Reflected ray

Incident ray

P3.6 Reflection and P3.9 Critical Angle

Reflection • Law of reflection states: Angle of incidence = Angle of reflection • Both are measured from the ‘normal’ • Can predict the path of a particular

reflected ray

Key word • Normal – line at right angle to a surface

Total Internal Reflection • Critical angle = the smallest angle of

incidence at which the angle of refraction is 90° or total internal reflection occurs.

• Greater the refractive index = the smaller the critical angle

• Calculation of the critical angle

Sin c nr = Sin r ni

• Light can travel along the boundary between the different mediums in some exceptional situations.

• Automatic windscreen wipers sense refraction of light when water is on the windscreen changing the medium from glass alone.

P3.10 – Using reflection and refraction

Optical Fibre Light ray travelling is consistently reflected back as it is at an angle greater than the critical one. The edge is acting like a mirror and laws of reflection are obeyed. Endoscope – look inside a patient.

Flexible rod of optical fibres. Light reflected off the inside of the body is

gathered and focussed to form an image.

Ultrasound – higher frequency than human hearing Travel through solid objects being partly reflected when the medium changes Medical scan transmit and receive the waves At the interface between tissues reflection occurs. Reflected rays converted into an image Used in diagnosis and treatment

Used to locate hard deposits like kidney stones e.g. high intensity ultrasound can break down kidney stones Treat injured muscles (easy to target the correct area

1. State the law of reflection

2. What is the ‘normal’?

3. What is the definition of critical angle?

4. How do you calculate the critical angle?

5. How do Automatic windscreen wipers

work?

P3.6 Reflection and P3.9 Critical Angle

1. Why is a light ray in an optical fibre always reflected back?

2. What is an endoscope 3. How does an endoscope work? 4. What is ultrasound? 5. What are some uses of ultrasound?

P3.10 – Using reflection and refraction

Facts • Ionising radiation – turns atoms to ions • More energy the x-ray has = more ionising • Higher frequency x-ray = more energy

X-ray machine • Evacuated tube containing 2

electrodes • Cathode (negative) is a wire

filament. When heated it emits electrons (electron gun). This is called thermionic emission.

• Anode (positive) made of metal. If there is a large potential difference the electrons are accelerated to the anode. Most kinetic energy is transferred to thermal energy but some is transformed into x-rays.

• Higher potential difference = x-rays with greater energy

• Tube is evacuated to prevent electrons colliding with other particles.

Comparing currents • Charged particles from cathode to anode

completing the circuit. • Increase temperature = increase the electrons

emitted = increases the X-rays produced.

Measuring current in X-ray machine I = current in amperes N = number of particles flowing each second q = charge on each particle in coulombs

I = N x q

P3.11 – X-rays

Kinetic energy m = mass of an electron in kg v = velocity of the electron in m/s e = charge on the electron V = potential difference in volts

KE = 1/2mv2 = e x V

P3.12 – Using X rays

Absorption of X-rays • Different materials absorb different amounts of x-rays • Denser material = more absorption = looks lighter on the x-ray photo Fluoroscopes • Show organs working • Detect blocked vessels • Consist of x-ray source and detector on digital video camera CAT Scans • X-ray source moves in circle around patient • Detectors opposite the source • Many cross-sectional images that can build up 3D image • Tumours detected with areas of brightness or dark patches

Keyword Inverse Square Law– the value of a physical property is inversely proportional to the square of the distance from the source.

Benefits Painless and non invasive Can eliminate the need for biopsy to decide on treatment. Risks Both give a dose of radiation equivalent to 10 yrs background radiation Increased risk of cancer so not recommended on children or pregnant females.

1. State 3 ways ultrasound can be used in either diagnosis and treatment

2. State the 3 main parts of an x-ray machine 3. If you increase the potential difference in the machine how does

it affect the x-rays?

4. What is Thermionic emission?

5. Complete the blanks below

Increase _______ the electrons emitted _______ the X-rays temperature produced.

6. How do you calculate current in the x-ray machine?

What is inverse square law?

P3.11 – X-rays

1. What is inverse square law? 2. State 2 uses of fluoroscopes

3. How does a CAT scan work?

4. Give 2 benefits and 2 risks of X-rays, Fluoroscopes and CAT scans

5. Complete the blanks below about absorption of X rays Denser _______ absorption looks ______ on X-rays

6. How do you calculate current in the x-ray machine?

P3.12 – Using X-rays

P3.13 – ECGs and Pulse Oximetry

Pulse Oximetry • 2 LEDs – one red light and the other infrared radiation • A detector to see the peaks in absorbance which gives a pulse rate • Oxygenated blood absorbs more infrared so machine can compare absorbency of each LED to work

out oxygen in blood. Pacemakers

– If action potentials do not spread across heart properly the pacemaker amplifies and transmits them so chambers contract correctly.

Action potential – change in voltage across a nerve cell (neurone) or cardiac muscle when and electrical

impulse travels along it.

1. Action potential is sent to each muscle cells to tell it to contract.

2. Starts in Atria (top chambers) 3. Body has a high proportion of water and salts

so conducts electricity 4. Action potentials will travel through the skin

and can produce an ECG picture of the heart electrical signals.

5. Heart has a regular pattern 6. Frequency of heartbeat in beats/seconds

Frequency, F (Hz) = 1 time period, T (second)

P3 Topic 3: P3.14 Beta and Positron radiation

• Atom – an atom consists of a small nucleus containing protons and neutrons and with electrons around it.

• Nucleons – protons and neutrons are known as nucleons. • Atomic number – same as proton number which is the number of protons in the atom • Mass number – same as nucleon number, which is the number of protons and neutrons in

an atom. • Beta particles – electrons (Beta-minus) or positrons (Beta-plus)

What is beta decay?

Beta minus decay – In beta minus decay, a neutron becomes a proton plus an electron. Beta minus radiation is made up of a stream of high energy electrons. They can penetrate paper but not thin sheets of metal. The particles are ionising. Beta-minus decay increases the atomic number by 1 but mass number is unaffected.

Beta plus decay – In positron or beta-plus decay, a proton becomes a neutron plus a positron. Positron decay decreases the atomic number by 1 but mass number remains unchanged.

The diagram shows how ionising radiation can be used as part of the system for controlling the thickness of paper produced in a paper mill.

1.Define the term action potential.

2.How is the frequency of heartbeats calculated?

3.What is the unit of measure for frequency?

4.How does a pacemaker work?

5.What 2 things can a pulse oximeter tell us?

P3.13 – ECGs and Pulse Oximetry

1.Describe two properties of beta radiation.

2.Describe two properties of positron radiation.

3.Describe the process of ß+ decay and ß- decay.

4.What happens to the proton number and mass number during each type of ß decay?

P3.14 Beta and Positron radiation

P3.15 Alpha and gamma radiation Radioactive emissions – there are three types, alpha, beta and gamma. • Alpha radiation – alpha particles are each made up of 2

protons and 2 neutrons. They are not very penetrating but are very ionising.

• Alpha decay – results in the atomic number decreasing by 2 and mass number decreasing by 4.

• Gamma radiation – are a type of electromagnetic radiation, it has no mass and causes no change to the atomic number or mass number. Gamma rays are very penetrating but not very ionising.

• Neutron radiation – sometimes in radioactive decay, a neutron is emitted. Neutrons have no charge, but they are as penetrating as gamma rays.

• Nuclear Reactions – Shows the reactants and products in a nuclear reaction. This reaction has to be balanced in terms of the total atomic mass number and total mass number which must be the same on both sides.

Alpha decay

Beta decay

Gamma decay

P3.15 Alpha and gamma radiation

Smoke detectors found in people’s homes use an alpha source such as americium. Alpha particles are capable of ionising particles in the air, breaking them up into positive and negative ions.

Uses of alpha radiation – A smoke detector

Remember!!! – In nuclear reactions: An alpha (α) particle has two protons, two neutrons and no electrons. It is therefore a helium nucleus and is shown as A β− particle is an electron and has a mass number of zero. It has the opposite charge to a proton so it has an atomic number of –1 (i.e. opposite to a proton) and is shown as A β+ particle is a positron. It has a mass number of 0 and a positive charge so is shown as having an atomic number of +1: A gamma ray has no mass and no charge and so is shown as

1. What happens to nuclei that have undergone radioactive decay?

2. Radium 226 emits an alpha particle. Complete the equation to show the products formed.

3. What effect does gamma radiation have on the mass number? Explain your answer.

P3.15 Alpha and gamma radiation

1.How does a smoke detector work?

2.Complete the table below of the properties of different types of radiation:

P3.15 Alpha and gamma radiation

Type Description Charge Penetration Ionisation ability

Alpha (α)

Beta (β-)

Gamma (γ)

P3.16 The N-Z Stability Curve • Isotopes - of an element have the same number of protons but

different number of neutrons. • Stable isotopes – isotopes which stay in their arrangement

indefinitely • Unstable isotopes – isotopes which decay by emitting

radioactivity. • N = Number of Neutrons • Z = Number of protons

Stability Curve or N-Z curve

The stability curve is important as it shows the patterns in the way that different isotopes behave. It compares different isotopes with regard to the numbers of protons and neutrons they have, and shows whether they are stable or not and, if not, what kind of emissions they release. • Each grey dot on the graph represents an isotope • The black dots represent stable isotopes • The other isotopes are unstable. • The straight black line is the N = Z line. Any isotope on that line

has the same number of protons and neutrons in its nucleus. Carbon-12 is an example of this.

• Heavier elements (those with a more massive nucleus) are nearer the top of the graph. They are not close to the N = Z line

P3.17 Quarks

• Quark – a particle from which protons and neutrons are made. Protons and Neutrons contain 3 quarks.

What is the role of quarks in beta decay?

Quark compositions in a proton and a neutron

Quarks Quarks exist within larger particles called hadrons (which include protons and neutrons). The two types of quarks we will consider are ‘UP’ and ‘DOWN’ quarks. • A Proton – consists of two UP quarks and one DOWN

quark • A Neutron – consists of two DOWN quarks and one UP

quark • Quarks can change from one into another – this

explains how a proton can change into a neutron and vice-versa.

• Beta plus decay – when an UP quark changes into a DOWN quark.

• Beta minus decay – when a DOWN quark changes into an UP quark.

What are quarks?

Charges on Quarks Up quarks have an electrical charge of +⅔. Down quarks have an electrical charge of -⅓. This explains why protons have a positive charge and neutrons have no charge

Quark Up Down

Mass 1/3 1/3

Charge +2/3 -1/3

Mass and Charge of Quarks

1. What does the N-Z curve show? 2. What does N stand for? 3. What does Z stand for? 4. Thinking about an N-Z curve, what type

of decay will an isotope with a Z value a) above 82 undergo? b) above the curve undergo? c) below the curve undergo?

P3.16 The N-Z Stability Curve

1. Which type and how many quarks does a) a proton contain b) a neutron contain?

2. What happens to the quarks during ß+ decay and ß- decay

3. Complete this table to show the mass and charge of up and down

quarks.

P3.17 Quarks

Quark Up Down Mass Charge

P3.18 Dangers of ionising radiation What are the dangers of ionising radiation?

• Mutations – changes in the structure of the DNA, which may then copied over to new cells.

• Dosage – in radiation exposure, it is the total amount of radiation absorbed by the person exposed to it.

• Dosimeter – is a film badge, developing the film reveals the dose of radiation received by the wearer.

Increase in radiation levels can: • Kill healthy cells – risk of damage to their

DNA. • Stimulate the growth of cancers • Cause mutations – the structure of the

DNA in cells can cause cancers or harmful changes to the function of genes, which are passed down to the next generation.

• Cause radiation burns – beta burns are mainly surface burns, gamma burns go deeper into the tissue and organs inside the body.

Protecting people from over-exposure • Increase the distance that medical staff

work from the source. • Shielding the containment of the

radioactive source • Minimise the time spent in the presence

of sources • Controlling the dosage of the radioactive

material used in patients for diagnosis or treatments

• Wear a dosimeter to monitor the levels of exposure and dose received by the wearer

P3.19 Radiation in hospitals How are radioactive substances used in hospitals?

• Radiotherapy – Use of ionising radiation to treat cancer by killing cancer cells or to reduce the size of a tumour with

• Internal radiotherapy – where the radioactive source is placed inside the body, e.g. placing iodine-131 next to the tumour in the patient

• External radiotherapy – where a gamma source or X-ray tube is used to apply a dose to the patient. • Palliative care = a condition that cannot be cured, but allows the patient to be in less pain to enjoy a

better quality of life. • Tracer – a radioactive substance that is injected into the body and emits gamma rays that can be

detected outside of the body to monitor how a part of the body is functioning. • PET Scans – Positron emission tomography – uses principle of positron-electron annihilation shows

the active areas of parts of the body that take up more of the injected tracer (more detail found in Topic 4: PET Scans slide).

Radiotherapy is used to treat cancers by killing cancer cells. It may also be used in palliative care. Cancers can be diagnosed using a tracer. Tracers will concentrate in particular organs or diseased or cancerous tissues and tumours. They usually have a short half-life, i.e. it will lose its radioactivity very quickly so other parts of the body are affected minimally. In a PET scan, the tracer emits a positron, this then interacts with an electron (annihilates) releasing two gamma rays in opposite directions. The PET camera then detects the gamma rays.

1. Describe two dangers of ionising radiation.

2. How is the safety of the patient and radiographer protected from over-exposure?

P3.18 Dangers of ionising radiation

1. Describe what is meant by palliative care.

2. Why do isotopes used in PET scanners have to be produced nearby?

3. Give two uses of radioactive substances in diagnosis of medical conditions.

P3.19 Radiation in hospitals

P3 Topic 4: P3.20 Collaboration and Circular Motion

• Particle physics – is the study of the nature and properties of sub-atomic particles and fundamental particles and their interactions.

• Circular Motion – motion of an object in a circle which requires centripetal force. • Centripetal Force – A resultant force acting inwards along the radius of the circle.

What are particle accelerators used for?

Circular Motion To keep the bucket moving in a circle, a resultant force acts inwards towards the centre of the circle along the radius. In the above example, the centripetal force is provided by the tension in the string in both diagrams above. If the bucket or rock are released, there is no longer any centripetal force and therefore no tension. The object will travel in a straight line at a tangent to the circular path it has been following.

Theories and models of particles are tested over time as other scientists repeat experiments and critically evaluate the work published in Scientific papers and journals. LHC – Large Hadron Collider – is a particle accelerator. It can accelerate beams of protons or ions to very high speeds in opposite directions to allow head-on collisions. Scientists then study the particles created in the collisions and may discover new particles.

P3.20 Cyclotrons

Cyclotron - A cyclotron is a particle accelerator. The particles start at the centre and follow a spiral path. The particles are accelerated to greater and greater speeds until they hit a target at the edge of the cyclotron. Positive ions produced at the centre of the cyclotron enter a uniform magnetic field created by D-shaped magnets or ‘dees’. The magnetic field deflects the ions into a circular path. Each time the ions cross the gap between the dees they are accelerated by the voltage. As the ions gain speed they follow a spiral path until they leave the cyclotron and undergo a collision with the particles in the target. Artificial radioactive isotopes can be produced when a beam of accelerated protons from a cyclotron is collided with the nucleus of a stable element. The nucleus of this element gains a proton and is changed into an unstable nucleus of a different element. Small cyclotrons are now used in hospitals to produce the short-lived isotopes needed in PET scanners.

• Cyclotrons – are particle accelerators in which moving charged particles are bent into circular or spiral paths (as in the LHC – Large Hadron Collider)

• Radioactive Isotope – An unstable isotope that emits radiation, such as alpha, beta or gamma radiation.

How a cyclotron works

1. How does a particle accelerator work and what do scientists hope to learn from it?

2. Define 'centripetal force'.

3. What is a Large Hadron Collider?

P3.20 Collaboration and Circular Motion

1. What causes particles to move in a circular motion in a cyclotron?

2. What are cyclotrons used to produce?

3. What is a radioactive isotope?

P3.20 Cyclotrons

P3.22 Collisions How is an elastic collision different to an inelastic collision? • Inelastic collision – a collision where kinetic energy (KE) is not conserved, some of the KE

is transferred to its surroundings, e.g. as sound or heat. • Elastic collision – a collision where there is conservation of kinetic energy. • Momentum – Mass x velocity of a moving object. The units are kg m/s. It is a vector

quantity which has both size and direction. • Conservation of Energy – states that energy cannot be created or destroyed. • Conservation of momentum – states that the total momentum before and after collision

remains unchanged.

Colliding objects have energy and momentum. Momentum is conserved in all collisions. In elastic collisions, kinetic energy is conserved but in inelastic collisions, kinetic energy is not conserved. The diagrams above show examples of elastic and inelastic collisions. In an elastic collision, the balls m1 and m2 collide and then carry on moving at speeds, v1 and v2. In an inelastic collision, the red and blue ball stick together and move at a speed of v.

Inelastic Collision Elastic Collision

P3.22 Momentum Calculations Solving problems using momentum conservation

Two trolleys collide and stick together. From the data below, calculate the velocity of the trolleys after the collision.

trolley A trolley B

mass = 3 kg mass = 5 kg

velocity = 8 m/s velocity = -4 m/s

momentum = 24 kg m/s (3 x 8) momentum = -20 kg m/s (5 x -4)

total momentum before collision = 4 kg m/s (24 + -20)

mass after collision = 8 kg (3 + 5)

momentum after collision = 4 kg m/s

velocity after collision = momentum / mass = 0.5 m/s

1. Compare and contrast elastic and inelastic collisions.

2. What is momentum? 3. What is conservation of energy? 4. What is conservation of momentum?

P3.22 Collisions

During an experiment a student pushes a glider of mass 400g along an air track with a velocity of 2.0m/s. It collides with a stationary glider of mass 600g which moves with a velocity of 1.6m/s. Find the velocity of the 400g glider after collision and show that the collision is elastic.

P3.22 Momentum Calculations

P3.23 PET Scanners Why do the radioisotopes used in PET scans produce pairs of gamma rays?

• Antimatter – is matter that has particles of the same mass and properties as their counterparts. E.g. the anti-matter of an electron is a positron.

• Positron – is the anti-mater of an electron which has the same mass as an electron but carries a positive charge.

• Annihilation – when an electron and a positron collide, they annihilate each other and produce 2 gamma rays photons which move away in opposite directions.

• Mass-energy equivalence – occurs when the masses of the annihilated electron and positron are converted into an equivalent amount of energy.

PET Scans - To produce a PET scan, a radioactive isotope that emits positrons and has a short half-life is injected into the patient’s blood. This isotope accumulates in various tissues of the body. The positrons from the decaying isotope meet electrons in the tissue surrounding the isotope. When this happens, a pair of gamma rays is produced moving in opposite directions. The gamma rays are detected by pairs of gamma ray sensors positioned around the person. Through analysing where the gamma ray pairs originate within the tissue, a picture of the internal organs can be produced.

PET Scanner Electron-Positron annihilation

P3 Topic 5: P3.24 Kinetic Theory • Kinetic theory – states that everything is made up of tiny

particles that are atoms or molecules. • Kinetic energy – the energy a particle has due to its

movement. Calculated using the equation K.E. = 1/2mv2, unit of K.E. is Joules (J).

• Pressure – is force per unit area and is measured in Pascals (Pa) where 1 Pa = 1 N/m2.

• Absolute zero – is a temperature of -273oC which is the temperature at which the pressure of a gas would be zero and the particles would NOT be moving.

• Kelvin temperature scale – measures the temperatures relative to absolute zero. The units are kelvin (K) and 1K is the same temperature interval as 1oC.

What is Absolute Zero? Absolute zero = 0K = -273oC

• A graph to show how the pressure of a fixed volume of gas changes with temperature.

• Temperatures are easily converted: • From Kelvin to Celsius – subtract 273 degrees • From Celsius to Kelvin – add 273 degrees

1. What is produced when an electron and positron are annihilated?

2. During annihilation, mass appears to have been lost. Explain this phenomenon in terms of conservation of mass.

3. Explain the use of radio isotopes in PET scanners

P3.23 PET Scanners

1. What is absolute 0?

2. What is 100o Celsius in Kelvin?

3. How does the pressure of a fixed volume of gas change with temperature?

P3.24 Kinetic Theory

P3.24 Kinetic Theory Particle movement in the three states of matter

Kinetic Theory 1. Gases are compressible (easily

squashed) and expand to fill up a container.

2. The temperature of a gas is a measure of the average kinetic energy of the particles in the gas.

3. The faster the average speed, the higher the temperature

4. Heating a gas increases the kinetic energy of particles so they move faster and temperature rises.

Particles and Pressure & Absolute Zero 1. The pressure of a gas is caused by the forces of moving particles on the walls of a

container. The faster the movement, the higher the number of collisions and more force will be exerted.

P3.27 Calculating volumes and pressures How can we calculate the pressure or volume of a gas? Volume and Pressure • If the volume of a gas increases at a constant temperature,

the pressure decreases. • Volume and pressure are inversely proportional • Volume and pressure are related by this equation:

V1P1 = V2P2 V1 and V2 are volumes in m3 and P1 and P2 are pressures in Pa.

Volume and Temperature If the temperature of a gas is increased at a constant pressure, the volume increases. Volume and temperature are directly proportional and are related by this equation:

𝑽𝟏= 𝑽𝟐 𝑻𝟏 𝑻𝟐

V1 and V2 are volumes in m3 and T1 and T2 are temperatures in K.

• V = Volume in m3

• P = Pressure in Pa • T = Temperature in K

Combining the equations The two equations on the left can be combined to give the one above

You will need to be able to select and use these relationships to calculate either P, V or T

• Draw a particle diagram to show the three states of matter.

• Explain the pressure of a gas in terms of particles.

• Explain the effect of changing temperature on the speed of particles in a gas.

P3.24 Kinetic Theory

1. What is the link between kinetic energy of particles in a gas and the Kelvin temperature scale?

2. What are the standard units used for volume, pressure and temperature?

3. A bicycle pump compresses 0.000025m3 of air to a volume of 0.000010m3. What is the pressure of the compressed gas?

P3.27 Calculating volumes and pressures