Lenses and the Eye

Question 1

What do convex lenses do?

Answer 1

They converge light rays at a focus

Question 2

What do concave lenses do?

Answer 2

They diverge light rays

Question 3

How do we describe the size of an image compared to the object?

Answer 3

Magnified or diminished

Question 4

How do we describe the way up of an image compared to the object?

Answer 4

Upright or inverted

Question 5

Do convex lenses produce a real or virtual image?

Answer 5

Real

Question 6

Do concave lenses produce a real or virtual image?

Answer 6

Virtual

Question 7

If an image will be diminished, inverted and real, where can it be used?

Answer 7

Projector

Question 8

If an image will be the same size, inverted and real, where can it be used?

Answer 8

Photocopier

Question 9

If an image will be magnified, upright and virtual, where can it be used?

Answer 9

Magnifying glass

Question 10

What is the point where parallel rays of light focus?

Answer 10

Principal focus

Question 11

What is the distance between the lens and the principal focus called and what is it measured in?

Answer 11

Focal length, metres.

Question 12

What is the power of a lens measured in?

Answer 12

Dioptres

Question 13

What are images from concave lenses always?

Answer 13

Upright, virtual, diminished

Question 14

How can a lens be given a shorter focal length?

Answer 14

More curved or made of a material with a larger refractive index

Question 15

Describe the steps taken to draw a ray diagram

Answer 15

1) Draw one ray from top of object through centre of lens
2) Draw a second ray from top of object parallel to principal axis, then when it reaches the lens, goes through the focal point.
3) Extend both rays until they meet at the top of the image.
4) For a concave lens, extend the second ray back through the focal point.

Question 16

How can you tell from a ray diagram if an image is real or virtual?

Answer 16

If it is virtual, it is formed on the same side of the lens as the object.

Question 17

How is light detected in a camera?

Answer 17

Photographic film or a CCD

Question 18

Retina?

Answer 18

Light sensitive cells that change the image to electrical impulses sent along the optic nerve to the brain

Question 19

Lens?

Answer 19

Changes shape to focus light onto retina and form a real image

Question 20

Cornea?

Answer 20

Protects eye

Question 21

Pupil?

Answer 21

Allows light into the eye

Question 22

Iris?

Answer 22

Changes size to limit the amount of light entering the eye

Question 23

Ciliary muscles?

Answer 23

Change the thickness of the lens by contracting and relaxing

Question 24

Suspensory ligaments?

Answer 24

Link the lens to the ciliary muscles and tighten and slacken

Question 25

Short sightedness?

Answer 25

Lens focuses light in front of the retina. Use a concave lens to spread light from distant objects out so the image focuses further back.

Question 26

Long sightedness?

Answer 26

Lens focuses light behind the retina. Use a convex lens to converge light from near objects so the image focuses further forward.