revision topic 11

Question 1

how does a lens work

Answer 1

lens work by changing the direction of light passing through it. each section of the lens acts like a tiny prism refracting the light that goes through the lense and out

Question 2

what is the convex lens

Answer 2

it is a lense that makes parrel lines focus on one place, it might be used as magnifying

Question 3

what is the principal focus in the convex lens

Answer 3

the point where the parallel rays are focused

Question 4

what is the concave lens

Answer 4

it makes parallel rays diverge

Question 5

what is the principal focus in the concave lens

Answer 5

the point where the rays appear to come from

Question 6

what is the focal length

Answer 6

it is the distance from the centre of the lens to the principal focus

Question 7

how is a real image formed by a converging(convex) lens

Answer 7

it is formed when an object is beyond the principal focus because when it is formed when light rays are focused onto a screen

Question 8

how is a virtual image formed by a converging (convex) lens

Answer 8

it is formed when the virtual image is before the principal focus because it is formed where rays appear to come from

Question 9

what is the formula of magnification

Answer 9

image height/object height

Question 10

the nature f the image formed by the lens depends on

Answer 10

1. the focal length

2. the distance from the object to the lens

Question 11

what is the principal axis

Answer 11

it is the line that is perpendicular to the centre of the lens

Question 12

how does a camera work

Answer 12

cameras are transitionally convex lens where a real image it is produced on a digital screen by the pixel and there are two rules for cameras

1. in distanced objects the distance between the lens and film as to be equal to the focal length
2. the nearer the object to the lens is the greater the distance from the lens to the film

Question 13

how is a virtual image formed in a concave lens

Answer 13

the image formed in the concave lens is always virtual upright and smaller than the object

Question 14

what is the job of the eye lens in the eye

Answer 14

it focuses light on the retina

Question 15

what is the job of the iris in the eye

Answer 15

a coloured ring of muscle it controls the amount of light entering the eye

Question 16

what is the job of the pupil in the eye

Answer 16

the central hole formed by the iris light enters from the pupil

Question 17

what is the job of the ciliary muscles in the eye

Answer 17

it is attached to the lens by suspensory ligaments it controls the thickness of the eye lens

Question 18

what is the job of the cornea in the eye

Answer 18

it is a transparent layer in the eye that protects it and helps focus light on the retina

Question 19

what is the job of the retina in the eye

Answer 19

the light-sensitive cells around the inside of the eye

Question 20

what is the human range of vision

Answer 20

25cm to infinity

Question 21

what happens if you are in a dim light

Answer 21

the ciliary muscles in the iris would make the pupil dilate allowing more light to be focused onto the retina from the eye lens

Question 22

compare the eye and the camera

Answer 22

the eye as a variable focus convex lens, and the camera has a fixed focus convex lens, the eye alters the thickness of the lens by the ciliary muscles, in-camera you can just adjust the lens position, they both form a real, inverted magnification less than 1 image, the iris control the width of the pupil, in-camera you can adjust the aperture stop, and the eye has the retina while the camera has CCD for image detection

Question 23

what is short sight and how does it happen and why does it happen

Answer 23

it is a defect that occurs when the eye cant focus on distant objects, it happens because the image is formed before the retina this is because the eye lens too powerful or the eyeball is too long

Question 24

how can a short sight be treated

Answer 24

by using a concave lens

Question 25

what is long sight and how does it happen and why does it happen

Answer 25

it is an eye defect that occurs when the eye cant focus on distant objects, it happens because the image is formed after the retina and this is because the eyeball is too short or the eye lens is weak

Question 26

how can a long sight be treated?

Answer 26

by using a convex lens

Question 27

the larger the refractive index

Answer 27

the more powerful the lens is, the shorter id focal length is, and the thinner and fatter the lens can be made because it needs to be less curved

Question 28

how can short sight be treated

Answer 28

by using an excimer laser to make part of the cornea slightly thinner having the same effect as using a concave lens