GCSE EDEXCEL PHYSICS TRIPLE [P3]

Pregunta	Respuesta
Topic 1 Radiation in treatment and medicine	Topic 1 Radiation in treatment and medicine
What are the methods that medical physicists can do to help doctors solve medical problems?	1) Cat Scans 2) Ultrasounds 3) Endoscopes 4) Ionising and non-ionising radiation
What is radiation?	Radiation is energy that originates from a source.
What does the intensity of radiation depend on?	1) The intensity of radiation decreases as the distance from the source increases. 2) The intensity of the radiation also depends on the medium that it is passing through.
What is the equation of Intensity?	Intensity = power of incident radiation / Area I = P -- A
Describe the refraction of light by converging and diverging lenses?	1) Converging lens are convex and they cause parallel rays of light to converge to a focus at the lens. 2) Diverging lens is concave - it caves inwards and causes parallel rays of light to diverge.
Relate the power of a lens to its shape?	If you have a more strongly curved lens, then it will increase the power of the lens.
What is the equation for power of a lens?	Power of lens (dioptre, D) = 1/focal length (metre, m)
What is the lens equation?	1/f = 1/u + 1/v f = focal length, u = object distance, v = image distance.
Identify the following features in a diagram of the eye – cornea, iris, pupil, lens, retina, ciliary muscles	Identify the following features in a diagram of the eye – cornea, iris, pupil, lens, retina, ciliary muscles
How is light focused?	Light is focused on the retina by the action of the lens and cornea.
What is the average adults human eye near point and far point?	It has a near point at about 25cm and a far point at infinity.
Explain the symptoms and causes of short sight?	1) Short-sighted people can't focus on objects that are far away - this happens if their fair point is closer than infinity. 2) Images of distant objects are brought into focus in front of the retina. 3) Short sight can happen for many reasons. The cornea and lens might be too powerful or the eyeball is too long. The cillary muscles might be unable to relax enough to change the shape of the lens to focus light on the retina.
Explain the symptoms and causes of long sight?	1) Long-sighted people can't focus clearly on near objects. This happens if their near point is further away from the normal. 2) Images of near objects are brought into focus behind the retina. 3) Long sight might happen because the cornea and lens are too weak or the eyeball is too short. The cillary muscles might not be able to contract enough to change the shape of the lens to focus light on the retina. 4) A lot of people become long sighted as they get older because the eye lens become stiffer on the cillary muscles become weaker - causing the eye to lose some of its focusing power.
What is the treatment for short sight and long sight?	Short sight can be corrected with diverging lens and laser eye surgery. Long sight can be corrected with converging lens and laser eye surgery.
What is refraction?	Refraction is when radiation changes direction as it enters a different medium.
How is TIR used in optical fibres?	Optical fibres work because of total internal reflection as light waves are reflected off the sides of a thin inner core of glass or plastic. The wave enters one end of the fibre and is reflected repeatedly until it emerges at the other end.
What are the uses of optical fibres in endoscopes?	1) An endoscope is a thin tube containing optical fibres that lets surgeons examine inside the body. 2) Endoscopes consist of two bundles of optical fibres. One is to carry light to the area of interest and one to carry an image back so that it can be viewed. 3) The image can be seen through an eyepiece or displayed as a full-colour moving image. 4) The big advantage of using endoscopes is that surgeons can now perform many operations by only cutting tiny holes in people.
What are the uses of ultrasound in diagnosis and treatment?	1) Breaking down kidney stones. 2) Pre-Natal Scanning of a Foetus. 3) Measuring the speed of blood flow.
Topic 2 X-rays and ECGs	Topic 2 X-rays and ECGs
How do you produce X-rays?	1) A filament acts as a cathode. The filament is heated which gives more energy to its electrons. Once they have enough energy, they escape. This process is called thermionic emission. 2) The electrons are then accelerated towards the anode by a potential difference between the cathode and anode. 3) Electron beams can be used to produce X-rays when the electrons collide with a metal target, some of their kinetic energy is converted into X-rays. 4) The glass tube contains a vacuum to prevent the electrons colliding with air particles. 5) A lead casing is put around the tube to absorb some of the x-rays so they're only aimed at the thing in question.
Explain why a beam of charged particles is equivalent to an electric current?	Current is the rate of flow of charge.
How does the absorption of X-rays occur?	By the thickness of the material through which the X-rays are travelling. The thicker a material, the more x-rays will be absorbed.
Describe how X-rays are used in CAT scans?	1) An x-ray beam rotates around the body and is picked up by thousands of detectors. 2) A computer works out how many of the X-rays are absorbed and produces a very high quality image. This is especially useful for diagnosing less obvious problems.
Describe how X-rays are used in fluoroscopes?	Fluoroscopes use x-rays to create moving images of patients insides.
Give a comparison of the risks and advantages of using X-rays for treatment and diagnosis?	1) X-rays can be harmful to us. Despite this, they're often still the best choice to treat or diagnose a patient. This is because the benefits of using it usually outweigh the risks. 2) Hospitals try to limit x-ray exposure and reduce risk to the patient as much as possible. 3) Using x-rays is a non-invasive procedure, this means the patient doesn't undergo incisions or surgery. This means the procedures are usually quick.
Explain how action potentials can be measured with an electrocardiogram (ECG) to monitor heart action?	1) The heart is a pump made of muscle, which is split up into four chambers - the atria at the top and the ventricles at the bottom. 2) When the heart beats, an action potential passes through the atria, making them contract. Seconds later, another action potential passes through the ventricles, making them contract too. 3) Once the action potential has passed, the muscles relaxes. 4) These action potentials produce weak electrical signals on the skin.
Relate the characteristic shape of a normal ECG to heart action?	1) The horizontal line is just the resting potential 2) The blip at P shows the contraction of the atria. 3) The QRS blip shows the contraction of the ventricles. It's a weird shape because you've got the relaxation of the atria going on there too. 4) The T shows the relaxation of the ventricles.
What is a pacemaker?	A pacemaker is a device used to regulate heart beat.
Describe the principles and use of pulse oximetry?	Pulse oximeters use light to measure the percentage of oxygen carried by the haemoglobin in a patient's blood. This is useful for monitoring the patient's health before and after surgery.
Topic 3 Production, uses and risks of ionising radiation from radioactive sources	Topic 3 Production, uses and risks of ionising radiation from radioactive sources
Evaluate the social and ethical issues relating to the use of radioactive techniques in medical physics?	1) Radiation is both useful and dangerous. We have to think whether the benefits of using it to treat an illness, outweighs the associated risks to the patients involved. 2) Some people may argue that if someone's quality of life could be seriously reduced after treatment, then it may not be worth undergoing it in the first place. Some people may refuse treatment because of the risk of getting these side effects. 3) Some people argue that it is unethical to test new treatments or drugs on animals.
Describe the properties of alpha?	Alpha 1) A helium nucleus 2) Slow and heavy 3) Strongly ionising 4) Stopped by paper, skin, etc.
Describe the properties of beta?	Beta 1) An electron 2) Light and fast 3) Moderately Ionising 4) Stopped by thin metal
Describe the properties of gamma?	Gamma 1) Electromagnetic radiation 2) No mass, very fast 3) Weakly ionising 4) Stopped by thick lead or very thick concrete
Describe the properties of positron?	Positron 1) An antiparticle of the electron 2) Light and fast 3) Moderately ionising 4) Stopped by thin metal
Describe the properties of neutron radiation?	Neutron Radiation 1) Neutron 2) More penetrative than alpha or beta and someones even more penetrating than gamma. 3) Aren't directly ionising, but they can be absorbed by the nuclei of atoms in the substances they pass through.
Recall the relative masses and relative electric charges of protons, neutrons, electrons and positrons?	Proton Relative Mass: 1 Relative Charge: +1 Neutron Relative Mass: 1 Relative Charge: 0 Electron Relative Mass: 1/2000 Relative charge: -1 Positron Relative Mass: 1/2000 Relative Charge: +1
In an atom the number of protons equal what?	The number of protons equals the number of electrons.
Describe the process of Beta - decay	1) Beta-minus decay is the emission of an electron from the nucleus. 2) Beta decay happens in isotopes that are neutron-rich (have too many neutrons than protons in their nucleus). When a nucleus ejects a beta particle, one of the neutrons in the nucleus is changed into a proton.
Describe the process of Beta + decay	1) Beta-plus decay is the emission of a positron from the nucleus. 2) In beta-plus emission, a proton gets changed into a neutron.
Explain the effects on the atomic (proton) number and mass (nucleon) number of Beta - decay?	The proton number increases by one, and the mass number stays the same.
Explain the effects on the atomic (proton) number and mass (nucleon) number of beta + decay?	The proton number decreases by one, and the mass number stays the same
Explain the effects on the atomic (proton) number and mass (nucleon) number of Alpha decay?	The proton number decreases by two, and the mass number decreases by four.
Explain the effects on the atomic (proton) number and mass (nucleon) number of Gamma radiation?	There is no change in the proton number or mass number of the nuclei
Describe the features of the N-Z curve for stable isotopes?	1) An isotope that lies above the curve has too many neutrons to be stable. 2) An isotope that lies below the curve has too few neutrons to be stable.
How can you identify isotopes as radioactive in the stability curve?	An isotope which doesn't lie on the curve is unstable. Unstable means radioactive.
What happens to nuclei with high values of Z (above 82)?	They undergo alpha decay.
What happens to an isotope above the curve?	An isotope above the curve has too many neutrons to be stable and will undergo Beta - decay.
What happens to an isotope below the curve?	An isotope below the curve has too many protons to be stable and will undergo Beta + decay.
Proton and neutron each contain three particles called what?	Quarks
Describe the arrangement of up and down quarks in protons?	A proton is made up of two up-quarks and one down-quark.
Describe the arrangement of up and down quarks in neutrons?	A neutron is made up of two down-quarks and one up-quark.
Use given data to explain the arrangement of up and down quarks in protons in terms of charge and mass?	Charge on proton = 2/3 + 2/3 + (-1/3) = +1 Mass of proton = 1/3 +1/3 +1/3 = +1
Use given data to explain the arrangement of up and down quarks in neutrons in terms of charge and mass?	Charge on neutron = 2/3 + (-1/3) + (-1/3) = 0 Mass of neutron = 1/3 + 1/3 +1/3 = 1
Explain the process of Beta - decay in terms of quarks?	It's a process that involves a down quark changing into an up quark (a neutron becomes a proton and an electron).
Explain the process of Beta + decay in terms of quarks?	It's a process that involves an up quark changing into a down quark (a proton becomes a neutron and a positron).
What happens to nuclei that have undergone radioactive decay?	They often undergo nuclear rearrangement with a loss of energy as gamma radiation.
Describe the dangers of ionising radiation?	1) Ionisation caused by radiation can kill a cell completely or damage it so it can't divide, causing tissue damages. 2) Radiation can alter the genetic material in a cell. This can cause mutations. 3) It can also make the cell divide and grow uncontrollably - this is cancer.
Explain the precautions taken to ensure the safety of people exposed to radiation?	1) Given the lowest possible doses of radiation and have a short exposure time. 2) Wear lead shielding to protect areas not being treated. 3) Staff should stand well away from sources or remotely control equipment, e.g. from another room. 4) Workers may stand behind lead screens or wear protective lead-lined clothing.
Compare and contrast the treatment of tumours using radiation applied internally or externally?	1) With internal radiation therapy, a radioactive material is placed inside the body into or near a tumour. This method gives a high dose of radiation to a small part of the body, so damage to normal tissue surrounding the tumour is limited. 2) Tumours can be treated externally using high energy x-rays or gamma rays aimed at the tumour. The radiation is carefully focused at the tumour, but some damage is still done to surrounding healthy cells. 3) The whole treatment using internal sources is usually shorter than using external sources of radiation. 4) Internal treatments may cause the patient to emit radiation after a source is inserted. 5) Internal treatments usually have no side effects, although there may be some discomfort from the implant. External temperatures like radiotherapy can have some short and long term effects. 6) Some uses of internal and external radiation therapy overlap, but they're often used to treat different parts of the body.
Describe palliative care?	Palliative care is treatment that reduces suffering without curing an illness.
Explain some of the uses of radioactive substances in diagnosis of medical conditions?	Tracers used to diagnose some medical conditions. 1) The tracer is injected into the patient or swallowed. An external detector follows its progress as it moves around the body. A computer uses these readings to create an image which shows where the strongest readings of radiation come from. PET Scanning can help diagnose illnesses. 1) PET scan shows areas of damaged tissue in the heart by detecting areas of decresed blood flow. This can reveal coronary artery disease and damaged or dead heart muscle caused by heart attacks. They can also record blood flow and activity in the brain. This helps diagnose illnesses like epilepsy. 2) PET scans can identify active cancer tumours by showing metabolic activity in tissue.
Explain why isotopes used in PET scanners have to be produced nearby?	So that it can act as a tracer, so after a few hours the tracer can move through the body to the organs.
Topic 4 Motion of particles	Topic 4 Motion of particles
Discuss how instruments, including particle accelerators, can help scientists develop better explanations about the physical world?	Scientists use huge particle accelerators to smash particles into each other at tremendous speed, to see what happens, what kind of radiation is given off, what new particles are created, etc. This gives clues about how the universe works, so scientists can develop better explanations about the physical world.
Discuss reasons for collaborative, international research into big scientific questions?	Particle accelerators are expensive, so not every country can afford its own. Also it's useful to combine the expertise of specialists, most are looking for the same sort of stuff. So sharing ideas is part of science anyway.
How is an object travelling in a circle motion?	1) Velocity is both the speed and direction of an object. 2) If an object is travelling in a circle it is constantly changing direction, which means it's accelerating. 3) This means there must be a resultant force acting on it. 4) This force acts towards the centre of the circle. 5) This force that keeps something moving in a circle is called a centripetal force.
Explain how particle accelerators called cyclotrons cause charged particles to move in a circular or spiral path?	1) The charged particles start at the centre of a cyclotron. 2) The cyclotron uses two hollow semicircular electrodes to accelerate the particle across a gap. 3) An alternating potential difference is applied between the electrodes - as the particles are attracted from one side to the other, their energy increases. 4) A magnetic field is used to keep the particles moving in a circular motion. 5) The magnetic field makes the particles spiral outwards as their energy increases.
Certain stable elements can be bombarded with proton radiation to do what?	Change them into radioactive isotopes.
Describe the use of particle accelerators (cyclotrons)?	To produce radioactive isotopes for medical purposes.
What is an elastic collision?	An elastic collision is where momentum is conserved and kinetic energy is conserved.
What is an inelastic collision?	Inelastic collision is where some of the kinetic energy is converted into other forms during the collision, but momentum is always conserved.
What can gamma rays be produced by?	The annihilation of an electron and a positron.
Is momentum conserved in positron/electron Annihilation?	Yes, momentum is conserved in positron/electron Annihilation.
Is mass energy conserved in positron/electron Annihilation?	Yes, mass energy is conserved in positron/electron Annihilation.
Explain the use of radio isotopes in PET scanners?	A positron-emitting radio isotope is injected into a patient. The emitted positrons collide with electrons in the organs, causing them to annihilate and emit high-energy gamma rays.
Topic 5 Kinetic theory and gases	Topic 5 Kinetic theory and gases
What is the kinetic theory for the state of matter solid?	Strong forces of attractions hold the particles close together in a fixed, regular arrangement. The particles don't have much energy so they can only vibrate about their fixed positions.
What is the kinetic theory for the state of matter liquid?	There are weaker forces of attraction between the particles. The particles are close together, but can move past each other, and form irregular arrangements. They have more energy than the particles in a solid, they can move in random direction at low speeds.
What is the kinetic theory for the state of matter gas?	There are almost no forces of attraction between the particles. The particles have more energy than those in liquids and solids, they are free to move, and travel in random direction at high speeds.
Explain the pressure of a gas in terms of the motion of its particles?	1) As gas particles move about, they bang into each other and whatever else happens to get in the way. 2) Gas particles are very light. When they collide with something, they exert a force on it. In a sealed container, gas particles smash against the container's walls, creating an outward pressure. 3) This pressure depends on how fast the particles are going and how often they hit the walls.
Describe the effect of changing the temperature of a gas on the speed of its particles?	If you increase the temperature of a gas, you give the particles more energy, so they move about more quickly. If you decrease the temperature of a gas, you're reducing the kinetic energy of the particles, so slowing it down.
Describe the term absolute zero, -273 degrees Celsius?	At absolute zero, the particles have as little kinetic energy as it's possible to get, so they're pretty much still (no movement).
How do you convert from degrees Celsius to kelvins?	You add 273.
How do you convert from kelvins to degrees Celsius?	You subtract 273.
What is the Kelvin temperature of a gas directly proportional to?	The kelvin temperature of a gas is directly proportional to the average kinetic energy of its particles.

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