P3 - The Eye

Question 1

What is the function of the cornea?

Answer 1

It is a clear surface which allows light through but protects the eye from dust and infection. MOST OF THE FOCUSSING OCCURS HERE.

Question 2

What is the function of the pupil?

Answer 2

Where light enters the eye. It gets larger in dim light and smaller in bright light.

Question 3

What is the function of the iris?

Answer 3

It changes size to make the pupil larger or smaller.

Question 4

What is the function of the lens?

Answer 4

It fine tunes the light to focus on the retina. ((Like a bag of jelly which can change shape to become thicker or thinner))

Question 5

What is the function of the retina?

Answer 5

It has light sensitive cells which send electric signals along the optic nerve.

Question 6

What is the function of the suspensory ligament?

Answer 6

It holds the lens in place.

Question 7

What is the function of the ciliary muscle?

Answer 7

They pull on the lens to change it’s shape.

Question 8

What is the function of the optic disc?

Answer 8

This is where the optic nerve meets the retina. There are no light sensitive cells here - the blind spot.

Question 9

What is the function of the optic nerve?

Answer 9

To take the electric signals to the brain.

Question 10

What happens when you focus on a near object?

Answer 10

The ciliary muscle relaxes. This makes the lens thicker so more refraction happens so that the light from the near object hits the retina.

Question 11

What happens when you focus on a far away object?

Answer 11

The ciliary muscle contracts to make the lens thinner which reduces the amount of refraction so that the light from the far away object hits the retina.

Question 12

What is the near point of vision?

Answer 12

25cm

Question 13

What is the far point of vision?

Answer 13

Infinity.

Question 14

What is long sight and how is it caused and fixed?

Answer 14

Long sight is where rays of light meet behind the retina instead of hitting it. This can be caused by the eyeball being too short of the lens not refracting enough. This problem can be resolved by the use of a converging/convex lens which makes the light converge more before it enters the eye so it will refract onto the retina.

Question 15

What is short sight, how is it caused and how is it fixed?

Answer 15

Short sight is where the rays of light meet in front of the retina instead of hitting it. This can be caused if the eyeball is too long or if the lens refracts too much. This problem can be resolved using a diverging/concave lens which makes the rays of light diverge slightly before entering the eye so the lens refracts the rays of light onto the retina.

Question 16

What happens to the ciliary muscles as we get older?

Answer 16

The ciliary muscles get tired as we get older so more people start needing glasses.

Question 17

How is the focal length of a lens determined?

Answer 17

Two factors determine the focal length of a lens. One if the refractive index of the material and the other is the curvature of the two surfaces on the lens. Materials with a higher refractive index will refract the light more which means thinner lenses can be used to produce the same power as a thicker lens made of a material with a lower refractive index. This knowledge is useful when making lenses for glasses and cameras etc.

Question 18

Compare the eye with a camera.

Answer 18

Type of lens

Eye - Converging lens with a variable focus

Camera - Converging lens with a fixed focus

Focusing adjustment

Eye - Ciliary muscles change the thickness of the lens

Camera - Lenses are moved which changes their position

Image produced

Eye and Camera - Real, inverted, magnification less than 1

Image detection

Eye - Light sensitive cells (retina)

Camera - Light sensitive film or CCD

Brightness control

Eye - Iris controls width of pupil

Camera - Adjusting the aperture.