Physics

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How do doctors diagnose medical problems?
visible light in endoscopes, x-rays in cat scanners and gamma rays in pet scanners
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what is ionising radiation?
radiation that causes an atom to giantess electrons ( gamma and x-rays)
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what is radiation?
any form of energy originating from a source in the form of waves and particles
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Describe the relationship between intensity and distance from the source
intensity decreases as distance from source increases. Intensity also depends on the density of the medium. The denser the medium the weaker the radiation
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what focuses light on the retina?
the lens and the cornea
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describe short-sightedness
far away objects are blurred, near objects are clear. Eyeball too long or cornea curved too sharply. rays of light focused in front of ret
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long-sightedness
near objects blurred, far objects clear., eyeBALL too short, lens too thick or not curved enough. lens can't bend the light enough. Image focuses behind the retina
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treatment of short sight
diverging lens. lens bends rays of light apart so cornea and lens focus light on the retina
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treatment of long sight
converging lens, refracts rays of light more so they meet on retina
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contact lenses
placed in front of cornea. allow oxygen to permeate through to the eye. need regular cleaning to prevent infection
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laser eye surgery
a finely controlled laser beam reshapes the front of the cornea, so the point at where the rays of light meet is changed
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converging lens
parallel rays of light are refracted and meet at the focal point.
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diverging lens
the focal point is the point of light which the rays of light seem to be coming from
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real images
have positive image distances and are from converging lens. they can be focused onto a screen
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virtual images
have a negative image distance and are from diverging lenses. can't be focused to a point on a screen
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reflection
the law of reflection states that the angle of incidence=the angle of reflection
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refraction
occurs when waves slow down when they enter a medium and change direction. Waves refract towards the normal if they slow down and away if they speed up
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ni
refractive index of medium travelling to
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nr
refractive index of medium travelling from
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optical fibres in endoscopes
used for keyhole surgery. endoscope contains a light source. light reflects off inside of body and is TIR into the eyepiece to form a clear image. no detail lost
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Ultrasound
waves reflect at interfaces. They are detected and converted into an image. used to locate and break up kidney stones. Can be focused and its intensity can be controlled
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Producting x- rays step 1
wire filament used as cathode. cathode heated to high temperature. this gives the electrons enough energy to escape the cathode. the electrons escape, so the cathode becomes an electron gun. this process is called thermionic emission
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producing x-rays step 2
there is an anode. a high potential difference is applied. this causes the electrons to accelerate rapidly towards the anode. then the electrons are put in an evacuated tube so they don't collide and lose energy
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step 3 - producing x-rays
the anode is made of metal so when the electrons collide they slow down. kinetic energy is transferred to thermal energy and some into x-rays. the higher the potential difference the more energy the x-rays have
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the inverse square law
states that intensity of radiation is proportional to the square of the distance
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x-rays
thicker material, more x-rays absorbed so it appears as black. less dense less x-rays absorbed so appears as white
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CaT SCAN
x-ray source and detector are moved around patient in circular motion. this builds up many cross-sectional images of the body. this is turned into a 3D image by a computer
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Fluoroscopes
x-ray soruce and detector are attached tho cameras. these show a patient's organs working
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Advantages and disadvatnatfes of fluoroscope and CAT Scans
+both painless and non invasive, eliminate the need for a biopsy - give the equivalent of 10 years background radiation, can't be used on pregnant women
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ECGS
an action potential is sent to muscles to tell them when to contract. the impulse is sent from the sion-atrial node, then it moves to the atrio-ventricular node
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How are these action potentials detected?
detected because the body has a high water percentage, which means electricity flows. An ECG is created by detecting these ECGS
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What does an ECG show?
the first section shows the heart's resting potential. the second shows how the action potential is used to make the atrium contract. the third shows the construction of the ventricles, which is called ventricular depolarisation. the final bit is rep
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How does a pacemaker work?
used to regulate heart action when a person's heart does not function properly. It detects action potential and increases them so they are transmitted to all heart chambers
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How does pulse oximetry work?
contains 2 LEDS and a detector. as the heart beats oxygenated blood surges. This absorbs more infrared but doesn't absorb light. the machine aliases the peaks of absorption to work out the pulse. the absorption of both types of LEDS is analysed
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Beta and Positron
both have masses of 1/2000. particles that are relatively ionising. beta has a charge of -1 and positron is +1
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B- decay
when a neutron becomes a proton and an electron. mass stays the same, atomic number increase by 1
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B+ decay
when a proton becomes a neutron and a positron. mass stays the same and the atomic number decreases by 1
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Alpha
high ionising, low penetration, charge 2+. causes atomic number to decrease by 2 and mass to decrease by 4
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isotopes
ones that are above the curve are radiation. the ones on the curve are not radioactive
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the N/Z curve
ones above the curve undergo B- decay, ones below the curve undergo B+ decay
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up quark
mass of 1/3 charge of +2/3
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down quark
mass of 1/3, charge of -1/3
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proton
2 up quarks, one down
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neutron
2 down quarks, 1 up
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Beta - decay
down quark changes into up quark, so neutron becomes a proton and an electron
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Beta + decay
up quark becomes a down quark, so a proton becomes a neutron and a positron
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Dangers of radiation
beta burns that look like sunburn. deeper gamma burns
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Precautions
increase distance from source, shielding, containment of source, minimise exposure time
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What is a dosimeter?
a film badge, developing the film reveals the amount of radiation. thin and thick plastic windows stop beta particles. lead casing stops beta an most gamma
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Palliative care
reducing the pain of the patient and improving their quality of life without curing them
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Tracers
the substance will concentrate in particular organs or diseased areas. usually as substance used by the body or made from a radioactive isotope
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Why do scientists collaborate?
to share expertise and share costs
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Circles and resultant force
for motion there must be an inward resultant force, this is called centripetal force. when the force is released the object travels in a straight line at a tangent to the path it had been following
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Cyclotrons
are particle accelerators in which moving charged particles are bent into circular paths. the centripetal force is produced by a constant magnetic field applied at right angles to the particles motion
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Voltage in cyclotrons
voltage is placed across the gap between the two D shaped magnetic fields, this accelerates the charged particles. the particles spiral outwards as their speed increases. when they leave the field they travel straight towards a target
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inelastic collisions
energy is not conserved but momentum is. 2 objects of equal mass move towards each other. kinetic energy is transfereed
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elastic collisions
momentum and kinetic energy are conserved. 2 objects move in same direction. 1st object hits the 2nd and kinetic energy is transferred to the 2nd object.
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annihilation
when a positron and electron collide and 2 gamma rays travelling in opposite directions are produced
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PET SCanners
during a pet scan annihilation is used to produce a pair of gamma rays that allow an internal image of body to be produced. the isotopes emit positrons. these travel and find electrons. annihilation occurs. the gamma rays are detected by sensors.
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movement of particles in a solid
particles are held together by strong forces. they can vibrate but not move freely
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movement of particles in a liquid
nonds aren't as storng so the particles can move past each other.
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in a gas
particles spread out and are compressible
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pressure of a gas
caused by the forces exerted when particles collide with the walls of the container
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absolute zero
-273 degrees- the temperature at which the pressure of a gas would be zero and the particles would be still
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kelvin temperature scale
measures temp relative to absolute zero. 0K=-273 DEGREES. Average kinetic energy is proportional to Kelvin
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Other cards in this set

Card 2

Front

what is ionising radiation?

Back

radiation that causes an atom to giantess electrons ( gamma and x-rays)

Card 3

Front

what is radiation?

Back

Preview of the front of card 3

Card 4

Front

Describe the relationship between intensity and distance from the source

Back

Preview of the front of card 4

Card 5

Front

what focuses light on the retina?

Back

Preview of the front of card 5
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