# Physics P3 1.8 More about the eye.

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What is a short-sighted eye?
An eye that can only see near objects clearly.
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What do we use to correct a short-sighted eye?
A diverging (concave) lens.
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What is a long-sighted eye?
An eye that can only see distant objects clearly.
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What do we use to correct a long-sighted eye?
A converging (convex) lens.
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How can a person with short sight see close objects clearly, but distant objects are blurred?
Because the uncorrected image is formed in front of the retina.
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What is short sight caused by?
The eyeball being too long or the eye lens being too powerful.
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How can a person with long sight see distance objects clearly, but close objects are blurred?
Because the uncorrected image is formed behind the retina.
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What is long sight caused by?
The eyeball being too short of the eye lens being too weak.
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What is the focal length of a lens determined by?
The refractive index of the material from which the lens is made and/or the curvature of the two surfaces of the lens.
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For a lens of a given focal length, how does the refractive index of the lens material affect the end product?
The greater the refractive index of the lens material, the flatter and thinner the lens can be manufactured.
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Which type of lens may be used to correct short sight?
A diverging lens.
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What defect of the eyeball may cause it to be long-sighted?
The eyeball is too short or the eye lens too weak.
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**YOU MAY BE ASKED TO COMPARE THE STRUCTURE OF THE EYE AND THE CAMERA**
**THE CAMERA HAS A LENS OF FIXED SHAPE BUT VARIABLE POSITION WHEREAS THE EYE HAS A LENS OF VARIABLE SHAPE BUT FIXED POSITION**
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## Other cards in this set

### Card 2

#### Front

What do we use to correct a short-sighted eye?

#### Back

A diverging (concave) lens.

### Card 3

#### Front

What is a long-sighted eye?

### Card 4

#### Front

What do we use to correct a long-sighted eye?

### Card 5

#### Front

How can a person with short sight see close objects clearly, but distant objects are blurred?