# Revision for Physics 3a

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What are X-rays?
X-rays are high frequency, short wavelength electromagnetic waves
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Name two materials that X-rays are absorbed by
Bones and metal
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What is a charge-coupled device?
CCDs are silicon chips that detect X-rays and produce electronic signals which are used to form high resolution images
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Describe how X-rays can be used to treat cancer
The X-rays are focused on the tumour using a wide beam, which is then rotated around the patient with the tumour in the middle
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What is ultrasound?
Ultrasound is sound with a higher frequency than the range of human hearing (20,000 Hz)
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Explain why ultrasound waves are used to take images of a foetus instead of X-rays?
Ultrasound waves are non-ionising, so won't damage the cells of the foetus
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What are the advantages of using CT scans over ultrasound waves?
CT scans produce detailed and high resolution images that can be 2D or 3D, but ultrasound images are typically fuzzy
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What is refraction?
Refraction is when waves change direction as they enter a different medium
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What is the formula for refractive index?
Refractive index (n) = sin i/ sin r
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Where is the principal focus of a converging lens?
It is where the rays hitting the lens parallel to the axis al meet
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Where is the principal focus of a diverging lens?
It is the point where rays hitting the lens parallel to the axis appear to all come from
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What type of lenses are used to make magnifying glasses?
Converging lenses
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What two things affect the focal length of a lens?
The refractive index of the lens material and the curvature of the two surfaces of the lens
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What is the far point of vision?
Infinity
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Give an approximate value of the near point for adults
25cm
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Describe two causes of short sight
The eyeball being too long, or by the cornea and lens system being too powerful (images of distant objects are brought into focus in front of the retina)
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Which type of lens can correct short sight?
A diverging lens
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Describe two causes of long sight
The eyeball being too short, or by the cornea and lens system being too weak (images of near objects are brought into focus behind the retina)
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Which type of lens can correct long sight?
A converging lens
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Describe how lasers can be sued to correct vision problems
A laser can be used to vaporise some of the cornea to change its shape, which changes focusing ability
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What is total internal reflection?
It is when when all light passed through an object is internally reflected, and no light comes out
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What happens if the angle of incidence is less than the critical angle?
Most of the light passes out, but a little bit of it is internally reflected
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What happens if the angle of incidence is greater than the critical angle?
No light comes out, as all of it is internally reflected
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What is an endoscope?
An endoscope is a thin tube containing optical fibres that lets surgeons examine inside the body
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Name one medical technique made possible by endoscopy
Keyhole surgery
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## Other cards in this set

### Card 2

#### Front

Name two materials that X-rays are absorbed by

Bones and metal

### Card 3

#### Front

What is a charge-coupled device?

### Card 4

#### Front

Describe how X-rays can be used to treat cancer

### Card 5

#### Front

What is ultrasound?