Lenses And The Eye

Question 1

Is the focal length of a diverging lens positive or negative?

Answer 1

Negative

Question 2

What does ‘u’ stand for?

Answer 2

The distance between an object and lens

It is always positive

Question 3

What does ‘v’ stand for?

Answer 3

Distance between image and lens

It is positive if the image is real and negative if the image is virtual

Question 4

How dos a more powerful lens (thicker) differ from a weaker one in terms of converging/diverging rays and focal length

Answer 4

It will converge/diverge rays more strongly and have a shorter focal length

Question 5

Cornea

Answer 5

Transparent ‘window’ with a convex shape and a high refractive index. It does most of the eyes focussing

Question 6

Aqueous humour

Answer 6

Watery substance that lets light pass through the pupil to the lens

Question 7

Iris

Answer 7

Consists or radial and circular muscles that control the size of the pupil.
Regulates intensity of light

Question 8

Lens and ciliary muscles

Answer 8

Lens acts as a fine focus, controlled by the ciliary muscles. When the ciliary muscles contract, tension is released and the lens takes a far more superficial shape. When they relax the suspensory ligaments pull the lens into a thin flatter shape

Question 9

When is the eye said to be accommodated

Answer 9

When the ciliary muscles are not fully relaxed

Question 10

Vitreous humour

Answer 10

Jelly-like substance that keeps the eyes shape

Question 11

Retina

Answer 11

Where images are formed, contains rods and cones

Question 12

Fovea

Answer 12

Centre of the retina with the highest concentration of cones

Question 13

Optic nerve

Answer 13

Carries signals from the rods and cones to the brain

Question 14

Far point

Answer 14

Furthest distance that the eye can comfortably focus on. For normally sighted people this is infinity

Question 15

Near point

Answer 15

Shortest distance the eye can focus on

Question 16

How do rods and cones send signals to the brain?

Answer 16

They contain chemical pigments that bleach when light falls on them which stimulates the cell to send signals to the brain via the optic nerve

Question 17

How are rods and cones reset?

Answer 17

By enzymes using vitamin A from the blood

Question 18

What is spatial resolution?

Answer 18

The ability to form separate images of objects that are close together
Two objects can only be distinguished from each other if there is at least one rod or cone between the light from each of them

Question 19

What is persistence of vision?

Answer 19

When an afterimage remains for a short amount of time on the retina after a bright image is removed

Question 20

How long do nerve impulses from the eye take to decay?

Answer 20

1/5th of a second

Question 21

Myopia
• what objects can the eye not focus on?
• when does it occur?
• where are uncorrected images brought to focus?
• type of lens used to correct

Answer 21

• distant objects
• when the lens and cornea are too powerful or the eyeball is too long
• in front of the retina
• diverging

Question 22

Hypermetropia
• what objects can the eye not focus on?
• when does it occur?
• where are uncorrected images brought to focus?
• type of lens used to correct

Answer 22

• near objects
• when the lens and cornea are too weak or the eyeball is too short
• behind the retina
• converging

Question 23

Astigmatism
• possible causes
• type of lens to correct
• information stated on the prescription

Answer 23

• an irregularly shaped cornea or lens which has different focal lengths for different planes
• cylindrical lens
• power and axis angle for correction

Question 24

Is the focal length of a converging lens positive or negative?

Answer 24

Positive