Lenses and Vision Defects

Question 1

(2) State the names of two parts of the eye that focus the light.

Answer 1

• cornea (1)

* lens (1)

Question 2

(6) Explain how long sight and short sight are different from normal sight and how one of these defects can be corrected.

Answer 2

• normal eye image forms on retina
• for all distances of objects
• short sight
• (clear) image of a distant object forms inside the eye / in front of retina
• corrected using diverging lens
• diverging the light / makes image distance longer
• long sight
• (clear) image of near object forms “beyond” the retina
• corrected using converging lens
• converging the light / makes image distance smaller

Other methods of correction include
• contact lenses which change the curvature of the cornea
• laser correction changes curvature of cornea

Question 3

(1) This oval lens can produce

Answer 3

both real and virtual images (1)

Question 4

(1) The diagram shows a converging lens with its focal length marked. Over this
diagram draw a converging lens of greater power and mark in its focal length.

Answer 4

Diagram showing
Convex lens, wider at the centre
and more curved (1)
shorter focal length identifiable
(1)

Question 5

(1) Diverging lenses always produce virtual, diminished images.
Which row of the table describes the images produced by a converging lens?

Answer 5

either real or
virtual
either magnified or
diminished

Question 6

(2) Describe how the power of a lens is related to its shape.
You may draw labelled diagrams if it helps your answer.

Answer 6

Effect of change in shape (1)
AND
Gives greater/ larger power (1)

Question 7

(1) The diagram shows the formation of an image produced by concave lens
On the diagram, draw and label the image produced.

Answer 7

Image, line at right angles to
principal axis to where rays
cross. Judge by eye
(1)

Question 8

(1) The diagram shows the formation of an image produced by concave lens
On the diagram, show and label the focal length of the lens.

Answer 8

Focal length, distance from
where virtual ray crosses
principal axis to centre of
concave lens.
Judge by eye
(1)

Question 9

(1) The diagram shows the formation of an image produced by concave lens
and is used to correct vision
Name this vision defect.

Answer 9

Short sight / short sightedness