P3.1.4 The Eye

Question 1

Describe and give the function of the cornea.

Answer 1

Tough, transparent covering over the front part of the eye. Convex in shape.

Refracts light as it enters the eye.

Question 2

Describe and give the function of the iris.

Answer 2

Coloured part of the eye that contains muscles which relax and contract to control the size of the pupil.

Controls how much light enters the pupil.

Question 3

Describe and give the function of the pupil.

Answer 3

Hole in the middle of the iris.

Allows light to pass through as it enters the eye.

Question 4

Describe and give the function of the lens.

Answer 4

Transparent, bi-convex, flexible disc behind the iris. It is attached to the ciliary muscles by the suspensory ligaments.

Refracts light to focus it onto the retina. The amount of refraction can be adjusted by altering the shape of the lens.

Question 5

Describe and give the function of the ciliary muscles.

Answer 5

Muscles connected to the lens by suspensory ligaments.

Adjust the shape of the lens to make it more or less curved, so as to increase or decrease the refraction of light.

Question 6

Describe and give the function of the suspensory ligaments.

Answer 6

Connect the ciliary muscles to the lens and hold the lens in place.

Slacken or stretch as the ciliary muscles contract or relax, to adjust the thickness and curvature of the lens.

Question 7

Describe and give the function of the retina.

Answer 7

The lining of the back of eye containing two types of light receptor cells. Rods are sensitive to dim light and black and white. Cones are sensitive to colour.

Contains the light receptors, which trigger electrical impulses to be sent to the brain when light is detected.

Question 8

How does the eye focus on a close object?

Answer 8

Ciliary muscles contract
Suspensory ligaments slacken
Low muscle tension on the lens

Lens becomes fat and more curved.

Question 9

How does the eye focus on a distant object?

Answer 9

Ciliary muscles relax
Suspensory ligaments stretch
High muscle tension on the lens

Lens becomes thin and less curved.

Question 10

What is the near point?

Answer 10

The nearest point to the eye in which the object remains in focus. 25cm for someone with normal vision.

Question 11

What is the far point?

Answer 11

The furthest point from the eye at which images are stil clear.

Question 12

What does it mean to be long sighted?

Answer 12

Can see near objects clearly, but cannot focus properly on distant objects because their far point is closer than infinity.

Question 13

What does it mean to be short sighted?

Answer 13

Can see distant objects clearly, but cannot focus properly on near objects because their point is further away than 25 cm - lens focusing too much.

Question 14

What is the range of vision?

Answer 14

Everything you can focus on between the near point and the far point.

Question 15

How would you correct the vision of someone who is short sighted?

Answer 15

With a diverging / concave lens.

Question 16

How would you correct the vision of someone who is long sighted?

Answer 16

With a converging / convex lens.

Question 17

What does a camera use instead of the retina to take a picture?

Answer 17

Photosensitive surface - photographic film / CCD

Question 18

What does a camera use instead of the iris to change the amount of light entering the camera?

Answer 18

Aperature - allows the user to control the amount of light entering the camera.

Question 19

What does a camera use instead of ciliary muscles and suspensory ligaments to change the focus?

Answer 19

Focusing screw - moves the lens back and forwards instead of changing its shape to adjust the focus.

Question 20

Give 2 reasons for being short sighted.

Answer 20

The eyeball being elongated - the distance between the lens and the retina is too great.

The lens being too thick and curved - light is focused in front of the retina.

Question 21

Give 2 reasons for being long sighted.

Answer 21

The eyeball being too short - the distance between the lens and retina is too small.

A loss of elasticity in the lens - cannot become fat enough to focus (often age-related).

Question 22

What do you measure the power of a lens in?

Answer 22

Dioptres / D.

Question 23

What is focal length of a lens is determined by?

Answer 23

The refractive index of the material that the lens is made from

The curvature of the two surfaces of the lens (how thick or fat the lens is)

Question 24

The power of a _______ lens is positive.

Answer 24

Converging.

Question 25

The power of a _______ lens is negative.

Answer 25

Diverging.

Question 26

How would you make lenses for glasses thinner without decreasing the power?

Answer 26

Use a material with a higher refractive index.