PHYSICS P3

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  • Created by: stelly_tn
  • Created on: 21-04-17 18:19
How are x-rays used in medicine?
They are absorbed by dense materials like bone and metal
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What does CAT stand for in scanning?
Computerised axial-tomography
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What do CAT scans do?
Use x-rays to produce a 2D image slice through the body, the x-rays are intense and strongly ionising, used to image soft tissue and bone
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What do endoscopes do?
Use visible light that reflect light along optical fibres to see inside a patient, used for keyhole surgery
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What are the medical uses of ultrasounds?
Breaking down kidney stones, pre-natal scanning of a foetus and measuring the speed of blood flow
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How do ultrasounds break down kidney stones?
Concentrate high energy wave beams at stone to turn into sand-like particles, pass out body in urine
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How do ultrasounds do pre-natal scanning?
Diagnose soft tissue problems and reflect off different tissue boundaries and times and distributions of echoes are processed by a computer to form an image
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What is radiation?
Radiation is energy that originates from a source. It can be in the form of a wave or a particle
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What happens to intensity when distance increases?
The intensity decreases
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What happens to intensity when density increases?
The intensity decreases
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What is the formula of intensity?
Intensity = power/area P=IxA
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What is intensity measured in?
W/m^2 power of incident radiation per unit area/meter squared
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What is refraction?
A change in direction caused by a change in speed
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What happens when light enters glass from air in terms of speed?
It slows down
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What happens if the wave hits a boundary at 90 degrees/along the normal?
It will slow down but will not change direction
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What happens when light hits a different medium?
Some light could pass or be reflected depending on the angle of incidence
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What does a converging lens look like?
Thin at edges and thick at the centre
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What does a diverging lens look like?
Thick at edges and thin in the centre
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What is the focal point of a converging lens?
The point in which all the light converge to a focus
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What is the focal point of a diverging lens?
The point where rays appear to come from when they disperse
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What is the focal length?
The distance between the middle of the lens
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What are the three rules for refraction in a converging lens?
An incident ray parallel to axis will pass through focal point on other side, an incident ray passing through focal point before entering will refract through lens and travel parallel to axis
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What are the three rules for refraction in a converging lens? (Pt 2)
An incident ray passing through centre of lens carries on in same direction
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At 2F what does the image look like?
Inverted, same size as object, located at 2F and a real image
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Between 2F and F what does the image look like?
Inverted, bigger than object, located beyond 2F and real image
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Nearer than F what does the image look like?
Right way up, bigger than object, located same side of the lens as object and virtual image
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What are the three rules for refraction in a diverging lens?
Incident ray parallel to axis refacts through lens and travels in line with focal point, incident ray passing towards focal point refracts through lens and travels parallel to the axis
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What are the three rules for refraction in a diverging lens? (Pt 2)
Incident ray passing through centre will carry on in same direction
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Is the image virtual or real for a diverging lens?
Virtual
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What is the formula for the power of a lens?
Power of lens = 1/focal length
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What is the unit of measurement for the power of a lens?
Dioptre
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What is the power of a converging lens always?
Positive
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What is the power of a diverging lens?
Negative
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What is the formula of the focal length?
1/f = 1/u + 1/v
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What is the image if v is positive?
Real
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What is the image if v is negative?
Virtual
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What units are focal lengths and distances of objects and images measured in?
Meters
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What is the image if the object is further than 1 focal length away from the lens?
Real
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What is the image if the object is closer than 1 focal length away from the lens?
Virtual
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What is the iris?
The coloured part of the eye made up of muscles that control the size of the pupil thus the size of the amount of light entering
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What is the pupil?
A hole in the iris
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What is the cornea?
A transparent window with a convex shape that focuses
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What are ciliary muscles?
Control the lens by contracting to make it fat, or relaxing to make it thin
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What is the retina?
Covered in light-sensitive cells which detect light and send signals to the brain via the optic nerve
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What is the light-sensitive cells made up of?
A collection of rods and cones, cones can see colour which only make up 5% of the total number
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What is the near point of an eye?
25cm
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What is the far point of an eye?
Infinity
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What does being short sighted mean?
Cant focus on distant objects, eyeball too long, ciliary muscles unable to relax enough
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What does being long sighted mean?
Cant focus on things close up, eyeball too short, ciliary muscles cannot contract enough
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What type of lens fixes short sightedness?
Diverging lens
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What type of lens fixes long sightedness?
Converging lens
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How do contact lenses work?
Sit on top of cornea and are shaped to compensate for the fault
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How does laser eye surgery work?
Vapourises tissue to change shape of cornea
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What is Snells Law?
N=Sin i/Sin r
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What does n, Sin i and Sin r stand for?
N = refractive index, Sin i is angle of incidence, and Sin r is angle of refraction
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What happens when light leaves with a higher refractive index and enters a material with a lower one?
It speeds up and bends away from the normal
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What happens if the angle of incidence is less than the critical angle?
Most of the light passes out but a little bit is internally reflected
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What happens if the angle of incidence is equal to the critical angle?
The merging ray comes out along the surface, and quite a bit of internal reflection
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What happens if the angle of incidence is greater than the critical angle?
No light comes out, total internal reflection
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What is the formula for the critical angle?
sin C = nr/ni
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What does nr stand for?
The refractive index of the stuff the lights travelling towards
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What does ni stand for?
The refractive index of the material the light starts from
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What is the critical angle for glass?
42 degrees
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How do optical fibres work?
Total internal reflection, light waves reflect off the sides of a thin inner core of glass/plastic, the wave enters one end of fibre and is repeatedly reflected until it emerges at other end, must be narrow enough to keep angles above critical angle
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How do endoscopes use optical fibres?
Use two bundles of them, one to carry light to the area and one to carry the image back to be viewed
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What is thermionic emission?
Releasing electrons from a surface
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What do you need to produce an x-ray?
A cathode, an anode, an evacuated gas tube and some thermionic emission
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Describe the process of making x-rays
Filament acts as a cathode, its heated and gives energy to electrons, once they have enough they boil off, this process is thermionic emission, theyre then accelerated towards anode by potential difference between the cathode and anode
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Describe the process of making x-rays (Pt 2)
Electron beams used to produce X-rays, when electrons collide with metal target (anode) some kinetic energy is converted to x-rays, glass tube contains a vacuum to prevent electrons colliding with air particles, which would decrease their energy
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Describe the process of making x-rays (Pt 3)
A lead casing is put around the tube to absorb some of the x-rays so they're only aimed at one thing i.e an arm at a hospital
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What is the formulas for kinetic energy
Kinetic energy = electronic charge x accelerating potential difference KE=1/2 x m x v^2 = e x V
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What is the formula for the size of the current produced?
Current = number of particles per second x charge on each particle I=Nxq
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What is the electronic charge?
1.6x10^-19
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Why are x-rays harmful?
They have enough energy to ionise which means removing electrons from atoms leaving them positively charged ions, which can lead to tissue damage or cancer
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What happens if you move twice as far from a source of radiation in terms of intensity?
You recieve 1/4 of the intensity
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What happens to the x-ray if you have a thicker material?
The more x-rays will be absorbed
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What are fluoroscopes?
They use x-rays to create moving images of patients insides
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How does a fluoroscope work?
By placing a patient between an x-ray source and fluorescent screen, different amounts of rays are absorbed as they pass through, the intensity will vary depending on what theyve passed through the body
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What can fluoroscopy do?
Diagnose problems in the way organs are functioning like movement of gastrointestinal tract
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How can x-rays be beneficial when used for treatments?
Limit x-ray exposure, better to properly diagnose than risk using wrong treatment, quick procedures
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What is between the inside of a muscle cell and the outside?
Potential difference/voltage
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What is the resting potential of a muscle cell?
-70 millivolts
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What do electrocardiographs measure?
The action potential of the heart
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Describe the typical ECG
The horizontal line is just the resting potential,the blip is the contraction of the atria, the large incline and fall is the ventricle contraction and also the atria relaxation, then the next blip is the relaxation of the ventricle
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Whats the formula for heart rate?
(Frequency = 1/time ) x60
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What a pacemaker?
A device that regulates heart beats
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How do pacemakers work?
Sends electric impulses to stimulate the heart to beat,
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What do pulse oximeters do?
Use light to check the %of oygen in the blood
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What is haemoglobin and what does it do?
The pigment which makes your blood red and carries the oxygen around your body
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How does the colour of haemoglobin represent oxygen content?
Its bright red if its rich in oxygen, purple if it has gave up its oxygen from its cells (called reduced haemoglobin)
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Describe how a pulse oximeter works
Transmitter that emits two beams and photo detector, placed on thin part of the body i.e finger, the beams pass through the tissue, on the way some of the red light is absorbed by blood reducing the amount detected by detector
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Describe how a pulse oximeter works (Pt 2)
The amount of light absorption depends on colour of blood, healthy people have a 95% oxyhaemoglobin
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What is the relative mass and charge of a proton?
Mass = 1 Charge = +1
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What is the relative mass and charge of a neutron?
Mass = 1 Charge = 0
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What is the relative mass and charge of an electron?
Mass = 1/1840 Charge = -1
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What are the properties of an Alpha particle?
A helium nucleus, slow and heavy, strongly ionising, stopped by paper/not penetrating
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What are the properties of a Beta particle?
An electron, light and fast, moderately ionising, stopped by thin metal/moderately penetrating
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What are the properties of a Gamma wave?
Electromagnetic radiation, no mass very fast, weakly ionising, stopped by thick lead or very thick concrete/very penetrating
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What is a positron?
A positive electron
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What makes a nucleus unstable?
Too many neutrons, too few neutrons, too many protons and neutrons together, too much energy
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What is a N-Z graph?
A graph showing the amount of neutrons (N) against the number of protons (Z0 for stable isotopes to create a curve of stability
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What if an isotope doesnt lie on the curve?
It is unstable
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What if an isotope lies above the graph?
It has too many neutrons
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What if an isotope lies below the graph?
It has too few neutrons
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When does Beta-minus decay happen?
When there is too many neutrons
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What happens to the isotope during Beta-minus decay?
The atomic number increases by one and the mass number stays the same
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When does Beta-plus decay happen?
When there are too few neutrons
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What happens to the isotope in Beta-plus decay?
The atomic number decreases by one, and the mass number stays the same
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When does Alpha decay happen?
In heavy nuclei with more than 82 protons
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What happens to atoms in Alpha decay?
The atomic number decreases by two and the mass number by four
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What is Beta-minus decay?
The emission of an electron from the nucleus
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What is Beta-plus decay?
The emission of a positron from the nucleus
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What is Alpha decay?
The emission of a helium nuclei
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When does Gamma radiation happen?
When the nuclei has too much energy
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What happens to atoms in Gamma radiation?
There is no change in the atomic or mass number
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What is the charge of an up-quark?
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What is the charge of a down-quark?
-⅓
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What is the relative mass of quarks?
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What is a proton made of in terms of quarks?
Two up-quarks and one down-quark
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What is a neutron made of in terms of quarks?
Two down quarks and one up-quark
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How do you change a neutron into a proton?
Changing a down-quark into an up-quark, beta-minus decay
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How do you change a proton into a neutron?
Changing an up-quark into a down-quark, beta-plus decay
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What is a tracer?
A radioactive isotope used to diagnose medical conditions
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How are tracers used?
Patient swallows it and a detector follows it around the body
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What does the thyroid gland absorb?
Iodine-131
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How do they reduce the radioactivity tracers emit?
The isotopes have short half-lives
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What does PET stand for in scanning?
Positron emission tomography
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What can PET scans do?
Show areas of damaged tissue in heart by detecting decreased blood flow, record blood flow and activity in brain, identify cancer tumours by showing metabolic activity, they have more metabolism because theyre growing like mad
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Describe how PET scans work
Inject patient with substance used by body containing positron emitting isotope with short half-life, over hour tracer goes around body
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Describe how PET scans work (Pt 2)
Positron meets electrons and annihilate, emitting high-energy gamma rays, the distribution of radioactivity matches up metabolic activity, more of the radioactive glucose injected is taken up by cells doing more work
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What dimension are PET scans?
3D
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Why do they use small doses of radiation in PET scans?
To prevent the amount of radiation that causes mutations
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What is internal radiation therapy?
A radioactive material is placed inside body near tumour
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What is external radiation therapy?
Using high energy x-rays or gamma rays aimed at the tumour
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Does internal or external radiation therapy cause side effects?
Internal has none aside from discomfort from implant, external does
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What are some of the side effects of radiotherapy?
Bowel damage, infertility, hair loss, sickness, skin irritation
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What is palliative care?
Treatment that reduces suffering without curing the illness
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Why are developing medical techniques can be regarded as controversial?
Could have harmful side effects but doctors dont know for sure but patients have a right to be aware, when a trial works how long until its offered for everyone
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What is centripetal force?
A force that keeps something moving in a circle
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What will a charged particle experience in a magnetic field?
A force
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How does a force affect a moving charged particle?
Itll make it perpendicular to tis direction of travel making the particle follow a curved track
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What does the direction of the force depend on?
The charge if its negative or positive
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What is a cyclotron?
A particle accelerator that uses a magnetic field to accelerate particles to very high energies along circular paths
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How does a cyclotron work?
The charged particles start at the centre of a cyclotron, an alternating P.D is applied between electrodes as particles are attracted to one side to the other and they are accelerated, magnetic field keeps them moving in circular motion
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How are radioactive isotopes produced using a cyclotron?
Bombarding stable elements with protons by proton enrichment which are usually positron emitters
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How have particle accelerators helped with knowledge of the universe?
They smash particles together at high speeds and see what radiation is given off to give clues on how the universe works, i.e Large Hadron Collider at Geneva recreating the conditions of the Big Bang
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What is the formula for momentum?
Momentum = mass x velocity
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What happens to momentum in a collision or explosion?
It is conserved
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What is an elastic collision?
Where momentum and kinetic energy is conserved
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What is an inelastic collision?
Momentum only is conserved, kinetic energy converted into other forms
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What is position/electron annihilation?
When they collide at each other the momentum is conserved and two gamma rays are produced
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What is the formula for mass energy?
E = m x c^2
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What is the speed of light?
3 x 10^8 m/s
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What are solids?
When strong forces of attraction hold particles together in a fixed regular structure, they particles cant move but only vibrate in fixed positions
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What are liquids?
When there are weaker forces of attraction between particles, they are close together but can move past each other
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What are gases?
Almost no forces of attraction between particles, have more energy than liquids and solids and are free to move randomly
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What does kinetic theory state?
Gases consist of small particles, they are constantly moving and colliding with the walls of their container, like moshers in a mosh pit
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What is absolute zero?
The coldest that anything can ever get, 0 kelvin
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What is 0 kelvin in degrees celsius?
-273 degrees
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What happens if you increase the temperature of a gas?
You give them more energy
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What is the relationship between kelvin temperature and kinetic energy?
Kelvin temperature of a gas is directly proportional to the average kinetic energy of its particles
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What is the formula for kinetic energy?
1/2mv^2
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What does kinetic energy say about colliding gas particles?
They create pressure because when they collide they exert a force on the walls creating an outward pressure
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What is the formula for volume at constant pressure?
Volume1 = volume2 x temperature1 (in K)/temperature2 (in K)
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V1 x P1 =
V2 x P2
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How do you test volume and temperature at a constant pressure?
Fill half a gas syringe and seal with rubber bung, bunsen burner to heat air, gas will expand pushing plunger outwards, volume increases, when it cools plunger will come in as gas contracts
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How do you test pressure and volume at the constant temperature?
Gas syringe filled with air to a pressure sensor, push plunger to compress the gas and reduce volume, increases pressure and more collisions will happen, pull plunger out and you increase the volume
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pressure x volume/temperature (in K) =
constant
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How are gases used in medicine?
Used to help patients breathe, gas canisters fitted with valve so flow of rate can be adjusted and controlled
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What is pressure measured in?
Atmospheres
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Why must gas canister be made of strong materials?
To hold gases under high pressures without buckling or splitting
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Other cards in this set

Card 2

Front

What does CAT stand for in scanning?

Back

Computerised axial-tomography

Card 3

Front

What do CAT scans do?

Back

Preview of the front of card 3

Card 4

Front

What do endoscopes do?

Back

Preview of the front of card 4

Card 5

Front

What are the medical uses of ultrasounds?

Back

Preview of the front of card 5
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