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P3 Exam Preparation

Prepare for your exam on gases, atoms, nuclei, and radiation with this comprehensive guide. Learn about absolute zero, gas pressure, beta decay, electron beams, cathode ray tubes, methods of seeing inside the body, and more.

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P3 Exam Preparation

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  1. P3 Exam Preparation

  2. Gases • Absolute zero = -273 ºC, 0 ºC = 273 K • Increasing the temperature of a gas increases the speed of its particles • The average kinetic energy of its particles is proportional to the temperature of a gas in Kelvin

  3. Gases • Gas pressure is caused by particles colliding with the container wall • The faster the particles (the higher the temperature) the greater the pressure • In all situations: P1V1 / T1 = P2V2 / T2

  4. Atoms and nuclei • Nuclei contain protons and neutrons • Neutrons are difficult to detect because the have no charge • As a result of β- or β+ decay nuclei often undergo rearrangement with a loss of energy as gamma radiation • In nuclear equations: • Mass is conserved (top number) • Charge is conserved (bottom number)

  5. Properties of Radation

  6. N - Z plot for stable isotopes α α n-2 p-2 β- N = Z β+ n+1 p-1 β- n-1 p+1 β+

  7. Fundamental and other Particles • Fundamental particles are not made up of other, smaller particles eg: • Electron • Positron (anti-electron) • Quark • Netrinos • Muons • A positron has the same mass as an electron and all other properties are opposite ie charge = +1

  8. Scientists are creating fundamental particles, such as anti-matter, in particles accelerators which smash particles into each other providing enough energy for the fundamental particles can exist on their own • These project are normally international collaborative projects due to the cost • The proton and neutron are not fundamental particles because they are made up of quarks

  9. Quarks

  10. Beta Decay and Quarks • β- decay involves a down quark changing into an up quark (one neutron becomes a proton and an electron) • β+ decay involves one up quark changing into a down quark (a proton becomes a neutron and a positron)

  11. Electrons and Electron Beams • Thermionic emission is when charged particles are emitted ‘boiled off’ a filament due to thermal energy • Uses of electron beams include: • TV picture tubes • computer monitors • oscilloscopes • the production of X-rays

  12. Cathode Ray Tubes Cathode (filament) Accelerating Anode Vacuum Electron strikes screen Electron Accelerated Kinetic Energy converted to Light Energy Steered by magnetic or electric field Thermionic Emission Steering plates Heating Current Accelerating Voltage Increasing heating current Increases numbers electrons boiled Increasing accelerating voltage Increases the KE of the electrons Both increase the brightness of the screen

  13. Cathode Ray Tubes • kinetic energy = electronic charge × accelerating voltage KE = e × V • a beam of electrons is equivalent to an electric current I = ( n x e ) / t You’ll be given: e = 1.6 x 10-19

  14. Beam Deflection • An electron beam, or a stream of charged particles (for example ink drops), can be deflected by the electric field between parallel charged metal plates • The amount of deflection increases when: • Mass of particle is decreased • The time in the field is increased • Larger plates • Slow particle

  15. Methods of ‘seeing’ inside the body

  16. Methods of ‘seeing’ inside the body • Refraction of a wave, is the change in direction (or bending) caused by the change in speed of the wave • This usually due to a change in density of medium

  17. TIR – Fibre Optics

  18. Radiation • Radiation is the spreading out of energy • Light (EM Spectrum) • Radioactive radiation (Alpha & Beta particles) • Sound

  19. Radiation • Medical applications of radiation: • Reflection • X-rays – bones may reflect the x-rays • Ultrasound scan (echocardiogram) • Total internal reflection • Endoscopes (Keyhole surgery, colonoscopy) • Absorption • Pulse oximetry • X-rays – bones may absorb the x-rays • Radiotherapy Remember the light is absorbed by the medium not the other way round

  20. Pulse Oximeter

  21. Energy and the body • Work done is equal to energy transferred • work done = force × distance (moved in the direction of the force) W = F × s • power = work done / time taken P = W / t • basal metabolic rate (BMR) is the minimum amount of energy required to stay alive

  22. Electricity in the body • frequency = 1 / time period f = 1 / T • Action potentials can be measured with an Electrocardiogram (ECG) to monitor heart action

  23. ECG Probes • The probes are able to measure the potential differences between the heart and the rest of the body • This potential difference is known as the action potential and makes the heart muscles contract

  24. Normal ECG Relaxation of the ventricles Contraction of the atria Contraction of the ventricles

  25. Heart Problems Bradycardia = low heart rate Tachycardia = high heart rate Arrhythmia = uneven heart rate

  26. Positron Emission Tomography (PET) • Radioactive tracer is injected into blood • Tracer emits positron • Positron annihilates an electron • Emits a pair of gamma rays in opposite directions • Gamma rays are detected by an array of gamma cameras • 3D map of body is created showing where the tracer accumulated

  27. Ionising radiation may cause: • Tissue damage • Mutations • The larger the dose of radiation the bigger the risk • Risk minimised by minimising the: • Intensity • Duration of exposure

  28. Tumours irradiated by radiation are affected more than normal cells • Palliative care is the treatment of the symptoms when the cause can not be cured • Social and ethical issues of (new/newer) techniques in medical physics: • Cost of treatment • Geographical availability • Potential risks

  29. Physics theory in medical care • intensity = power of incident radiation/area I = P/A • Double the distance => Quarter the Intensity I α 1 / r2 r = distance from source • Intensity depends on the nature of the medium the radiation is travelling through: Higher density => Higher absorption => Lower Intensity of radiation

  30. Physics theory in medical care • balancing nuclear equations that use thermal neutrons • In nuclear equations: • Mass is conserved (top number) • Charge is conserved (bottom number)

  31. Collisions • Energy conservation Total Energy Before = Total Energy After ½ m1 v12 + ½ m2 v22 = ½ m1 v1’2 + ½ m2 v2’2 + Sound & heat Energy etc • Momentum conservation Total Momentum Before = Total Momentum After m1 v1 + m2 v2 = m1 v1’ + m2 v2’

  32. Physics theory in medical care • The bombardment of certain stable elements with proton radiation can result in making them into radioactive isotopes that usually emit positrons • The production of gamma rays by annihilation of electron and positron as the rest energies (E = mc2) are converted from matter into (lots of) pure energy – gamma rays

  33. Physics theory in medical care • Annihilation of electron and positron to form gamma rays is an example of momentum and mass energy conservation: • Energy of gamma ray = rest energies of particles + KE of particles • Pairs of gamma rays are given out in opposite direction to maintain momentum

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