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GCSE level optics questions

Q18.

 

(a) Glasses may be used to correct defects of vision. Some glasses have been designed with lenses that can be adjusted to give different focal lengths.

Suggest one advantage of using adjustable lenses in glasses.

Any one from:

They don't need replacing if your eyesight changes - OR they can be adjusted to see near or far objects OR you only need one pair of glasses.

Saying 'They focus on objects at different distances' was classed as insufficient to gee you the mark - you needed to say why this was an advantage.

They don't need an optician/specialist to prescribe them.

They can be re-used by other people was insufficient to get a mark - but, let's face it - that is a good point.

A comment that they are cheaper than traditional glasses was ignored - they are probably dearer initially but in the long run may prove cheaper.

 

[1 mark]

(b) Explain how the human eye forms an image. Your explanation should include:

how a normal eye causes light from objects at different distances to form an image

why long sight and short sight cause blurred images.

Do not include diagrams in your answer.

This type of question is marked in two ways:

- the examiner looks for relevant points

- but also for a logical sequence...

It is not just a 'tick fest' - but a marker does look to see how many relevant points you have made, then considers how you have strung them together to put your answer into a 'level'

Level 3:

Clearly explains how an image is formed by the eye

and

either

Explains how the lens changes shape to focus light from objects at different distances

or

Correctly identifies that in long sight the image is focused behind the retina and for short sight it is focused in front of the retina
5 - 6 marks
Level 2:

Explains how an image is formed by the eye

and

either

Identifies that the lens changes shape to focus light from objects at different distances

or

Gives the reason why long or short sight gives a blurred image
3 - 4 marks
Level 1:

Describes how an image is formed by the eye

or

Identifies that the lens changes shape to focus light

or

Gives the reason why long or short sight gives a blurred image
1 - 2 marks
Level 0:

No relevant information
0 marks

 

Examples of the physics points that should be made in the response:

Explain how a normal eye forms an image:

Light enters the eye through the pupil

Light is refracted at the cornea

Light is focused by the lens and the cornea

The image should be focused on the retina

The image is inverted, real and diminished

Explain how light from objects at different distances forms an image:

For objects at different distances the lens changes shape

The ciliary muscles pull the suspensory ligaments changing the shape of the lens

For distant objects the lens becomes less powerful

For nearby objects the lens becomes more powerful

Explain why long and short sight cause blurred images:

In long and short sight the (focused) image does not form on the retina

In long sight, the image would form behind the retina

In short sight, the image forms in front of the retina

[6 marks]

(Total 7 marks)