P3 Medical physics

This is all of the second topic for the old specification Edexcel gcse physics

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Medical physics
Refraction is caused by waves changing direction
Waves slow down they bend towards the normal
Light enters glass/plastic it slows down
Wave hits boundary at 90 not change direction
Total internal reflection depends on the angle of incidence
Less than critical angle- most light is reflected
Critical angle- ray comes out along the surface
Greater than critical angle- no light comes out and total internal reflection
Optic fibre- use visible light/ infrared
Carry pulses of light or infrared(IR) radiation
Work because of internal reflection
Fibre must be narrow keep angle above critical- must not bend
so sharply
Endoscopes is a thin tube containing optical fibres
Two bundles of optical fibres
One to carry light to the area of interest
One to carry an image back so that it can be viewed
Seen through- eyepiece, or full colour moving image on a TV screen
Advantage- perform operation by keyhole surgery
Pulse oximeters use light to check the percentage of oxygen in the blood
Monitoring patients health before and after surgery
Used regularly
in intensive care, during anaesthesia and in the recovery room
in case of respiratory failure to monitor how well the body is oxygenated
investigating sleeping disorders
neonatal intensive care- many premature babies need ventilator to help them breath
Blood is bright red with a lot of oxygen(oxyhaemoglobin) and purple when it less (reduced
1 molecule of haemoglobin can carry up to 4 molecules of oxgen
It has a transmitter- emits 2 beams of red light
It has a photo detector to measure light
Placed on a thin part of the body
Beam of light passes through the tissue- some light absorbed by blood reducing amount of light
detected by detector
Amount of light depends colour depends oxyhaemoglobin content- people normally have a
minimum of 95%
Reflection pulse oximetry reflects light through red blood cells
Work done is energy transferred
Work done= force x distance

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Power is the rate of doing work
Power= work done/ time taken
Metabolic rate is the rate in which your body uses energy per sec/ min/day/hour
Basal metabolic rate is the rate you burn energy at rest
Tells you the minimum amount of energy needed to keep your body working
To measure- no food for 12hrs- lie down so they're fully rest- amount of heat energy generated is
measured over a certain time and used to find BMR
Factors that affect BMR
Children have a…read more

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Intensity of radiation is the rate of which energy arrives at 1m2 of surface
"Rate of energy" is power so....
Intensity = power/area
Sum it up: intensity of radiation is equal to power of radiation divided by the area it falls on
Intensity of radiation depends on distance from source
Intensity of radiation depends on the area its spread over e.g.…read more

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All the mass of the electron have been converted to energy- E=mc2
(Positron Electron Tomography) PET scanning involves Positron/Electron annihilation
Shows organ or tissue function
Better than x-rays, because x-rays shows only structure
1. Shows area of damage tissue in the heart by detecting areas of decrease flow- reveal coronary
artery disease and damaged/ dead heart cells caused by heart attacks
2. Identify active cancer tumours by showing metabolic activity in tissue. Cancer cell higher
metabolism than healthy cells- grow rapidly
3.…read more


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