P3 : Medical Applications of physics

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  • Created by: KAustria
  • Created on: 18-05-14 06:25
What are the features of X rays?
1. Part of the electromagnetic spectrum 2. HIgh frequeny 3. Short wavelength
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What are the properties of X rays?
1. They affect photographic film the same way light does 2. Absorbed by metal and bone 3. They are transmitted by healthy tissue 4. Ionisaing
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What are Charge-coupled devices (CCDs)?
They are used to form electronic images of X rays which allows images to be stored more easily and safely
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Describe how a traditional X ray would work.
1. photographic film is placed under the patient 2. X rays travel pass through the body and into the photographic film 2. X rays hits film the film goes black 3. Bone absorbs x rays so leaves a white shadow on film 3. Fractures are dark areas on bone
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What are CT scanners?
Scanners that use X rays to produce digital images of a cross-section through the body. Various images taken from different angles can be combined to make 1 3D structure.
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When a patient under goes a CT scan to observe their stomach they are given a supplement containing barium - why is this?
This is because the stomach is made out of soft-tissue therefore it is filled with a contrast medium which absorbs x rays so that it can be seen on an X ray image.
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What are the disadvantages of X rays?
X rays are can cause ionisation can damage living tissue when they pass through.
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What are thr uses of X rays?
1. Scans 2. Treat cancerous tumours on body surfaces.
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What should workers expose to x rays do to protect themselves?
Wear film badges and shield themselves with lead screens
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What frequencies can the human ear detect?
Frequencies between 20Hz and 20 000 Hz
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How do ultrasound waves behave when they are emitted?
WHen a wave hits a boundary between two different materials, part of the wave is reflected. The wave travels back to the detector.
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How can time be used to detect how far away a boundary is?
The velocity of the speed is multiplied with the time it took for the wave to travel back.
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When calculating the distance of the boundary, what should you do the time and why is this?
You should divide the time by 2 because the time read is the time it took for the ultrasound to travel from the emitter and back again.
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How are ultrasound used in medical treatment?
1. Removing Kidney stones 2. Pre natal scanning
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Why is ultrasound used in prenatal scanning and not x rays?
X rays can cause ionisation which can damage the cells of the developing baby, whilst ultrasound isn't ionising.
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What is refraction?
The change of direction of light as it passes from one transparent substance to another. As it hits another boundary it changes speed which causes it to change direction.
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What is the refractive index?
IS a measure of how much a substance can refract light.
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How do you calculate the refractive index?
1. n = sine of the angle of incidence / sine of the angle of refraction.
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When a light ray crosses from glass to air, what direction does it refract?
It refracts away from the normal and a partially reflected ray is een.
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As the angle of incidence increases..
The angle of refraction is increases until the refracted ray emerges along the boundary.
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What is the critical angle?
The critical angle is the angle of incidence of a light ray in a transparent substance which produce refraction along the boundary.
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What happen when the angle of incidence is beyond the critical angle?
The angle undergoes total internal reflection, which means the angle of reflection is equal tot he angle of incidence.
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How is refractive index and critical angle related?
n - 1/ sin of the critical angle.
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Wat is an endoscope?
A device used to look inside a patient's body without cutting it open.
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Describe the features of an endoscope?
1.It contains bundles of optical fibres, which are very thin and flexible glass fibres. 2. Light travels through the fibers by TIR
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Why is the colour of laser light used in endoscope matched with the tissue type?
To produce maximum absorption.
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Describe how eye surgery on the retina is carried out by laser light?
1. passes straight through cornea at the front 2. Absorbed by the retina at the back
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What do converging lenses do to light rays?
Light rays pass through the lense so that they converge into a point called the principal focus.
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What is the focal length?
The distance form the centre of the lens to the principal focus.
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IF the object is further away from than the lens than the principal focus, what type of image is formed?
1. Inverted 2. Real image
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If the obhect is nearer the the lens than the focal point, what is the image formed?
1. Upright 2. Virtual image formed behind the object. 3. the image s magnified.
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What do diverging rays do to rays of light?
Parallel light that passes through a diverging lens are refracted so that they diverge away from the principal focus.
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What is the image produced in a diverging lens?
It is always virtual.
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What is the difference between virtual and real images?
Real images are produced with light rays crossing. Virtual is the opposite.
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What is the line through the centre of the lens called?
Principal axis.
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Describe the the three construction rays in a ray diagram?
1. Ray parallel to the axis is refracted through the principal focus 2. Ray through the centre travels straight on 3. Ray through the focal point is refracted parallel to the principal axis.
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What lens does a camera use?
Uses a converging lens to forma real image of an object or an array of CCDS
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What is the function of the cornea? What does the cornea and eye lens do?
1. Light enters through the cornea 2. Focus light on the retina
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What does the iris do?
Adjusts the size of the pupil to control the amount of light entering the eye.
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What do ciliary muscles do?
Alter the thickness of the lens to control the focusing of the eye.
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What is the retina?
The light sensitive cells around the inside of the eyes.
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What is the range of vision of a human?
25 cm to infinity.
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What is the power of lens measured in?
Dioptres, D
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What is the vision like fr someone with short sight?
See close objects clearly but distant images are blurred because of the uncorrected image if formed in front of the retinea.
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What causes short sight?
1. Long eye ball 2. Eye lens is too powerful.
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How can short sight be corrected?
Using a diverging lens
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What is the vision like for someone with long sight?
1. Can see distant objects clearly but close objects are blurred because the uncorrected image is formed behind the retina.
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What causes long sight?
1. Eye ball is too short 2. Eye lens is too eak.
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How can Long sight be corrected?
With a diverging lens
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What are the 2 factors which determine the focal length of a lens?
1. Refractive index of lens 2. The curvature of the lens
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In lenses, the greater the refractive indec..
The flatter and thinner eye lenses are manufactured.
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Other cards in this set

Card 2


What are the properties of X rays?


1. They affect photographic film the same way light does 2. Absorbed by metal and bone 3. They are transmitted by healthy tissue 4. Ionisaing

Card 3


What are Charge-coupled devices (CCDs)?


Preview of the front of card 3

Card 4


Describe how a traditional X ray would work.


Preview of the front of card 4

Card 5


What are CT scanners?


Preview of the front of card 5
View more cards


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