P3 Physics

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  • Created by: wafflypig
  • Created on: 22-06-16 12:36
Give 5 uses of radiation in medicine
Break down kidney stones. Pre-natal scanning. Measuring speed of bloodflow. Endoscopes. CAT scans. X-rays.
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How do kidney stones get broken down?
Ultrasound is concentrated into a small area and the stone breaks into small particles, passed in urine
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How does pre-natal scanning work?
Ultrasound is reflected off the different densities of different tissues and the time/distribution is sent to computer and an image is generated
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How is bloodflow speed measured?
Ultrasound is real-time so it can show how far something has moved and how long it took. From this, speed can be calculated
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What is ultrasound?
Sound with a frequency higher than 20,000Hz (20KHz)
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How do endoscopes work?
Light is carried through optical fibres through TIR and can be used for keyhole surgery
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What does CAT stand for?
Computerised Axial Tomography
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How do CAT scans work?
The machine produces intense beams of X-rays to produce a picture of a 2-D slice through the body. Unlike X-rays, they can be used for soft tissues too
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How do X-rays work?
The X-rays are absorbed by the high density material (e.g. bones and bombs in suitcases) and turn bright under a radiographer's camera
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What is radiation?
Energy that originates from a source
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Give 4 types of radiation
Alpha, beta, gamma, light, sound, microwaves etc etc
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Which 2 things does the intensity of radiation depend on?
Distance from source and what the radiation is passing through.
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What kind of distribution of radiation does a candle produce?
Spherical
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Where is the radiation more intense?
Nearer the source
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What kind of substances absorb more radiation, making it less intense?
Dense
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What is refraction?
A change in the light's direction due to a change in speed - caused by a changing density
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What kind(s) of image can a converging lens produce?
BOTH real and virtual
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What kind(s) of image can a diverging lens produce?
Virtual ONLY
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What is the name of the imaginary line going through the middle of a lens?
Horizontal optical axis
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What is focal length?
The distance from the centre of the lens to the focal point
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At 2F, is the image real or virtual?
Real
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At 2F, what is the orientation of the image?
Inverted
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At 2F, what is the size of the image?
Same as object
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At 2F, where is the image produced?
At +2F
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Between F and 2F, where is the image produced?
Beyond 2F
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Between F and 2F, what is the size of the image produced?
Bigger than the object
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Between F and 2F, is the image real or virtual?
Real
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Between F and 2F, what is the orientation of the image?
Inverted
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At closer than F, is the image real or virtual?
Virtual
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At closer than F, what is the orientation of the image?
The right way up
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At closer than F, what is the size of the object?
Much bigger
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At closer than F, where is the image produced?
Same side as the object
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When drawing ray diagrams, which two lines do you need?
One going straight through the middle and one going from the top of the object then through the focal length?
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A lens with a higher power will be thinner, true or false?
FALSE, it will be thicker and therefore have a shorter focal distance
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What kind of image do diverging lenses produce?
Virtual, always
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What is focal length always measured in?
Metres, M
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What is the screen at the back of the eye called?
Retina
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Which muscles control the lens?
Ciliary
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When ciliary muscles contract, is the power of the lens greater or smaller?
Greater - the lens gets fatter
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What is the near point?
The minimum distance an eye can comfortably focus at (usually about 25cm)
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What is the far point?
The maximum distance an eye can focus comfortably.
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For normal sighted people, where is the far point?
Infinity
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What can't short sighted people focus on?
Distant objects
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What can't long-sighted people focus on?
Near objects
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When are people short sighted?
When the far point is at less than infinity and the focal point falls SHORT of the retina leaving blurry images
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When are people long sighted?
When the near point is further away than normal and the focal length falls behind the retina
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Why might old people get longsightedness?
Their ciliary muscles get weaker so the power of the lens decreases so focal point gets greater
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Why might anyone get shortsightedness?
When the eyeball is too long or lens is too powerful (ciliary muscles contract too much)
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What type of lens corrects shortsightedness?
Diverging
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What type of lens can correct longsightedness?
Converging
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Which two parts of the eye do the focusing?
Cornea and lens
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What cells are sensitive to light?
Cones and rods
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Give two ways (other than glasses), vision problems can be corrected
Contact lenses and laser eye surgery
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How do contact lenses work?
They are put on top of the cornea and make it the correct shape so it can have the correct power
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How does laser eye surgery work?
Reshapes the cornea so that the power of the cornea can be adjusted to suit
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What is Snell's Law for n?
n = sin(i)/sin(r)
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What does refractive index mean?
It shows us how much light light will refract in a specific material (a higher refractive index means it refracts more)
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What is TIR?
Total Internal Reflection
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What is the critical angle?
The angle of light entering the material at which it leaves in line with the boundary at 90 degrees to the normal with some being reflected back into the material
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At greater than the critical angle, what happens?
TIR
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What is Snell's Law for the critical angle?
Sin(C) = nr/ni
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What is nr?
The refractive index of the substance that the light will travel INTO TO
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What is ni?
The refractive index of the substance that the light will leave
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What is the n of air?
1
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What is the purpose of the outer core on an optical fibre?
Protection
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Which is denser, inner or outer core?
Inner to ensure TIR
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Why must the fibre be narrow and not bend sharply anywhere?
To ensure that the angle is kept above critical so TIR can happen
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What is an endoscope?
2 bundles of optical fibres
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What are the two bundles of optical fibres in an endoscope used for?
One to take light there and one to bring it back
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What is the advantage of using endoscopes?
You can do keyhole surgery which has a shorter recovery time
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What is thermionic emission?
Releasing electrons (discharging) using heat
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Which three things do you mainly need to produce X-rays?
A cathode, an anode and an evacuated gas tube
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How are X-rays produced?
The cathode loses its electrons through thermionic emission and the accelerate towards the anode due to PD and opposite charge. At the metal plate (anode), some of their kinetic energy is converted to X-rays
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How can X-rays harm body cells?
Ionisation. They have high Hz, so they have a high energy and can knock electrons off
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If you move twice the distance away from the source of radiation, by how much area has the distribution increased?
4
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What do fluoroscopes do?
Use X-rays to capture moving images of the insides of a patient's body
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How do fluoroscopes work?
X-rays pass through the body and because some has been absorbed, there will be differences in the intensity. The areas exposed to x-rays fluoresces
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What would you use to record bloodflow?
A fluoroscope
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What images do CAT scan produce?
2D
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How do CAT scans work?
X-ray beams are rotated around and detected at the other side. A computer works use how many X-rays have been absorbed and a 2-D slice is produced onscreen
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Which is more dangerous, CAT scans or xrays?
CAT scans
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What is resting potential?
The potential difference between the outside and inside of a muscle membrane
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What is action potential?
An increase in voltage that makes muscles contract
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What do electrocardiographs measure?
Action potential of the heart
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What is a pacemaker?
A device used to regulate heartbeat
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When is a pacemaker used?
When the natural pacemaker of the heart pulses a voltage irregularly or not often enough
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How do pacemakers work?
There are 2 electrodes attached to the heart and the electrical current stimulates the action potential to make the heat contract and beat.
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What is a pulse oximeter?
An electronic device that uses light to check the percentage oxygen levels in blood
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What kind of haemoglobin is bright red?
Very oxygenated
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What kind of haemoglobin is purply?
When it has given up its oxygen
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How do pulse oximeters work?
They emit 2 beams of red light from one side of a finger and see how much is absorbed. How much is absorbed depends on the colour of the blood (red = less absorbed)
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What is a positron?
A positively charged electron that is the antiparticle to an electron
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What is neutron radiation?
Emitted neutrons
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When does beta- decay happen?
When there are too many neutrons
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When does beta+ decay happen?
When there are too few neutrons
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When does alpha decay happen?
When nuclei are too heavy
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When is gamma emitted?
When nuclei have too much energy
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In beta- decay, what happens to the atomic and mass numbers?
Atomic = increases by one, mass = stays the same
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In beta+ decay, what does a proton change into?
A neutron
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In beta- decay, what does a neutron change into?
A proton
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In beta+ decay, what happens to the mass and atomic numbers?
Atomic = decreases by one. Mass = stays the same
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In alpha decay, what happens to the mass and atomic numbers?
Atomic = decreases by 2. Mass = decreases by 4
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What are protons and neutrons made up of?
Quarks
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Which quark has a charge of +2/3?
Up
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Which quarks(s) have a mass of 1/3
Both up and down
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Which quark has a charge of -1/3?
Down
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What makes up a proton?
2 up quarks and 1 down quark
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What makes up a neutron?
2 down quarks and 1 up quark
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Why do protons turn into neutrons?
Because one of their up quarks turns into a down quark
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Why are electrons/positrons emitted after a quark change has occurred?
To balance the charges
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Which two kinds of radiation can be used in medical tracers?
Beta- and gamma
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How do tracers work?
A radioactive isotope is swallowed by the patient and a G-M tube tracks its progress through the body. Can be used to show problems in the alimentary canal
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Which radioactive element builds up in the thyroid gland?
Iodine-131
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What radiation do PET scans use?
Positron
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What is antiparticle annihilation?
When two particles collide and release nothing but energy. (E.g. electron + positron = gamma rays)
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Other cards in this set

Card 2

Front

How do kidney stones get broken down?

Back

Ultrasound is concentrated into a small area and the stone breaks into small particles, passed in urine

Card 3

Front

How does pre-natal scanning work?

Back

Preview of the front of card 3

Card 4

Front

How is bloodflow speed measured?

Back

Preview of the front of card 4

Card 5

Front

What is ultrasound?

Back

Preview of the front of card 5
View more cards

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