# Medical applications of physics

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• Created by: Emily_O
• Created on: 15-11-13 21:01
How are x-rays used in hospitals?
To make images and CT scans; to destroy tumours at or near the body surface
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What are ultrasound waves?
Sound waves with a frequency above 20,000Hz
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How are ultrasound waves used in medicine?
Ultrasonic scanning and the destruction of kidney stones
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What is refraction?
The change of direction of light as it passes from one medium to another
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How does a lens form an image?
By refracting light
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What is refractive index?
A measure of how much a substance can refract a light ray
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Refractive index =
sin i (angle of incidence) divided by sin r (angle of refraction)
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What is the the critical angle?
The angle of incidence of a light ray in a transparent substance that produces refraction along the boundary
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When does total internal reflection occur?
When the angle of incidence of a light ray in a transparent substance is greater than the critical angle
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How are endoscopes used?
To see directly inside the body
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What do converging (convex) lenses do to parallel rays?
Focuses them to a point called the principal focus
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What do diverging (concave) lenses do to parallel rays?
Make them appear spread out as if they came from a point called the principal focus
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How is a real image formed?
By a converging lens if the object is further away than the principal focus
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How is a virtual image formed?
By a diverging lens and, if the object is nearer to the lens than the principal focus, a converging lens
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Magnification =
image height / object height
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Iris
Controls amount of light entering the eye
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Eye lens
Focuses light onto the retina
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Retina
Light-sensitive cells around the inside of the eye
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Cillary muscles
Attatched to the lens by suspensory ligaments and changes the thickness of the eye lens
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Pupil
Central hole formed by the iris where light enters the eye
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Cornea
Transparent layer that protects the eye and helps to focus light onto the retina
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What causes long sightedness?
The eyeball being too short or the eye lens being unable to focus
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What causes short sightedness?
The eyeball being too long or the eye lens being unable to focus
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What type of lens is used to cure long sightedness?
Converging
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What type of lens is used to cure short sightedness?
Diverging
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Power of a lens equation
P = 1 / f (P - power in dioptres, D ; f - focal length in metres, m
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## Other cards in this set

### Card 2

#### Front

What are ultrasound waves?

#### Back

Sound waves with a frequency above 20,000Hz

### Card 3

#### Front

How are ultrasound waves used in medicine?

### Card 4

#### Front

What is refraction?

### Card 5

#### Front

How does a lens form an image?

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