1. Topic 1 Applications of Physics

2. P3.1 Radiation in Medicine
Facts:
Intensity is an example of a compound measure (its units are determined by the units used in the calculation)
Standard units = W/m2
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.
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.
Intensity (I) = power of incident radiation in Watts (P)
W/m area in Metres squared (A)
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

3. 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
Eye structure diagram

4. Short and long sightedness
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

6. P3.5 Different lenses Power of a lens = 1
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
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 =
F u v
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

7. P3.5 Different lenses
Lens Equation – links the object distance (u), the image distance (v) and the focal length (f)
1 =
f u v

8. P3.6 Reflection and P3.9 Critical Angle
Key word
Normal – line at right angle to a surface
P3.6 Reflection and P3.9 Critical Angle
Incident angle i
Reflected angle r
Reflected ray
Incident ray
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
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
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.
Sin c nr =
Sin r ni

9. P3.6 Refraction Sin i nr = Sin r ni
Refractive index = speed of light in air
speed of light in substance
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
normal
Angle of incidence
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
image
Angle of refraction
actual location
Sin i nr =
Sin r ni
nr - refractive index of medium ray is travelling into
ni - refractive index of medium ray is travelling from

10. 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

11. P3
Topic 2 X-rays and ECG

12. P3.11 – X-rays Facts Ionising radiation – turns atoms to ions
More energy the x-ray has = more ionising
Higher frequency x-ray = more energy
P3.11 – X-rays
X-ray machine
Evacuated tube containing 2 electrodes
Cathode (negative) 9s 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
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

13. P3.12 – Using X rays
Keyword
Inverse Square Law– the value of a physical property is inversely proportional to the square of the distance from the source.
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
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.

14. P3.13 – ECGs and Pulse Oximetry
Action potential – change in voltage across a nerve cell (neurone) or cardiac muscle when and electrical impulse travels along it.
Action potential is sent to each muscle cells to tell it to contract.
Starts in Atria (top chambers)
Body has a high proportion of water and salts so conducts electricity
Action potentials will travel through the skin and can produce an ECG picture of the heart electrical signals.
Heart has a regular pattern
Frequency of heartbeat in beats/seconds
Frequency, F (Hz) = 1
time period, T (second)
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.

15. P3
Topic 3 Production, uses and risks of ionising radiation from radioactive sources.

16. P3 Topic 3: P3.14 Beta and Positron radiation
What is beta decay?
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)
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.

17. P3.15 Alpha and gamma radiation
What are alpha and gamma decay?
Alpha decay
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.
Beta decay
Gamma decay

18. P3.15 Alpha and gamma radiation
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
Uses of alpha radiation – A smoke detector
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.

19. P3.16 The Stability Curve How is the N-Z curve used?
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
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
Stability Curve or N-Z curve

20. P3.17 Quarks What is the role of quarks in beta decay?
Quark – a particle from which protons and neutrons are made. Protons and Neutrons contain 3 quarks.
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.
Quark compositions in a proton and a neutron
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
Mass and Charge of Quarks
Quark Up
Down
Mass
1/3
Charge
+2/3
-1/3

21. 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

22. 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.

23. Topic 4 Motion of particles

24. P3 Topic 4: P3.20 Collaboration and Circular Motion
What are particle accelerators used for?
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.
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.
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.

25. P3.20 Cyclotrons How a cyclotron works
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.
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.
How a cyclotron works

26. 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.
Inelastic Collision
Elastic Collision
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.

27. 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 ( )
mass after collision = 8 kg (3 + 5)
momentum after collision = 4 kg m/s
velocity after collision = momentum / mass = 0.5 m/s

28. 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.
Electron-Positron annihilation
PET Scanner

29. Topic 5 Kinetic Theory and Gases

30. P3 Topic 5: P3.24 Kinetic Theory
What is Absolute Zero?
Absolute zero = 0K = -273oC
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.
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

31. P3.24 Kinetic Theory Particle movement in the three states of matter
Gases are compressible (easily squashed) and expand to fill up a container.
The temperature of a gas is a measure of the average kinetic energy of the particles in the gas.
The faster the average speed, the higher the temperature
Heating a gas increases the kinetic energy of particles so they move faster and temperature rises.
Particles and Pressure & Absolute Zero
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.

32. P3.27 Calculating volumes and pressures
How can we calculate the pressure or volume of a gas?
V = Volume in m3
P = Pressure in Pa
T = Temperature in K
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:
𝑽 𝟏 = 𝑽 𝟐 𝑻 𝟏 𝑻 𝟐
V1 and V2 are volumes in m3 and T1 and T2 are temperatures 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