Lenses

Question 1

When light passes from a lighter medium to a denser medium _______

Answer 1

it bends TOWARDS the normal

Question 2

when light passes from a denser medium to a lighter medium ______

Answer 2

it moves away from the normal

Question 3

what is a lens?

Answer 3

A lens is a piece of any transparent material with two faces, of which at least one is curved. Each surface of a lens is a part of a sphere. The center of such a sphere is called the center of curvature (C). The centre of a lens is called optical centre (O)

Question 4

Convex lens is called _______ why?

Answer 4

converging lens
since a convex lens actually converges light at a principal focus that is why…..

Question 5

concave lens is called ________

Answer 5

diverging lens

Question 6

convex lens is

Answer 6

Thicker in the middle and thinner at the edges

Question 7

concave lens is

Answer 7

thinner in the middle & thicker at the edges

Question 8

denoted letter and 2nd name of the focal point?

Answer 8

(F) principal focus

Question 9

what is the principal focus?

Answer 9

In case of a convex lens, the light rays parallel to the principal axis after refraction through the lens meet at a point called the Principal focus

Question 10

focal length?

Answer 10

(f)
The distance between the optical center (O) and focal point (F) of the lens is called focal length (f)

Question 11

The convex lens is called _______ why?

Answer 11

converging lens
since a convex lens actually converges light at a principal focus that is why…..

Question 12

what is centre of curvature (C)?

Answer 12

Centre of a sphere

Question 13

what is (O)?

Answer 13

centre of the lens is called optical centre (O).

Question 14

principal axis?

Answer 14

The line passing through the O and C of the faces of the lens is called pa or oa

Question 15

why is the principal focus of a convex lens real?

Answer 15

as the light rays meet at a point after refraction through the convex lens

Question 16

why the principal axis focus point of a convex lens is real?

Answer 16

as the light rays meet at a point after refraction through the convex lens so the focus point is real

Question 17

why the principal axis focus point of a concave lens is virtual?

Answer 17

it is because the light rays diverge out and appear to be coming from a point called the principal focus that is why the F is virtual

Question 18

what is rarer medium and denser medium?

Answer 18

rare medium (lighter) eg. air
denser medium (thick) eg. glass

Question 19

what happens when an object is placed beyond 2F?
how does the image appear?

Answer 19

the image is formed between F & 2F and the image is real, inverted, and smaller in size than the object

Question 20

when is the image formed beyond 2F? how does the image appear?

Answer 20

when the object is between F and 2F the image is real inverted and larger in size than the object

Question 21

when is the image of an object formed at infinity? what is the image like?

Answer 21

when the object is at F
it cannot be shown in the diagram because rays become parallel after refraction.

Question 22

what happens when an image is between O and F?

Answer 22

rays after refraction diverge out & do not meet on the other side of the lens. A virtual image will be formed at a point where the rays meet when extended backward. the image will be magnified and erect

Question 23

what is an aperture?

Answer 23

The aperture is an opening in the diaphragm behind the lenses. This can be made smaller or larger as required.

Question 24

image formation in the camera?

Answer 24

pg. 143

Question 25

short-sightedness is also called?

Answer 25

Near sightedness myopia

Question 26

which lens is used in myopia?

Answer 26

concave lens diverges light before they enter the eye and hence, the rays are refracted by the eye lens again to meet at the retina

Question 27

long-sightedness is also called?

Answer 27

far sightedness hyperopia

Question 28

which lens is used in long-sightedness?

Answer 28

convex lens converges light rays before they enter the eye. After entering the eye, they are further bent by the eye lens to meet at the retina.

Question 29

causes of near sightedness?

Answer 29

when eye lens becomes much thicker or eyeball become too long

Question 30

causes of long sightedness?

Answer 30

when eye lens becomes thin or the eye ball becomes too short

Question 31

causes of long sightedness?

Answer 31

when the eye lens becomes thin or the eyeball becomes too short

Question 32

what is - and + in lens

Answer 32

focal length

Question 33

the focal point of a concave lens is ?

Answer 33

virtual

Question 34

the focal point of a convex lens is ?

Answer 34

real

Question 35

what is a ray diagram?

Answer 35

is a drawing showing the path of light rays

Question 36

what part of eye has cells?

Answer 36

retina

Question 37

differences of cones and rods?

Answer 37

| Cones | Rods | | --- | --- | | Cones are active in bright light. | Rods are active in dim light. | | They are found near the centre of retina. | They are found on the outside of retina. | | Cones produce color visions. | Rods don’t produce color visions. | | Cones have a very fast recovery time. | Rods have a very slow recovery time. | | Cones perceive color vision. | Rods percieve black & white objects. |

Question 38

sclera's properties

Answer 38

thick & hard

Question 39

cornea's properties

Answer 39

transparent & hard

Question 40

what happens when you look at a distant object?

Answer 40

ciliary muscles relaxed and the lens become thinner

Question 41

what happens when you look at a closer object?

Answer 41

ciliary muscles contract, the lens becomes thick so that the image is formed on the retina instead of forming at a point beyond it.

Question 42

image formation in the concave lens?

Answer 42

pg 142

Question 43

the focal length of thick convex lens is _______ focal length of thin convex lens is ________

Answer 43

shorter larger

Question 44

what types of image is formed by a concave lens?

Answer 44

The image will always be virtual, erect, and smaller in size than the object.

Question 45

what types of image is formed between O & F?

Answer 45

virtual magnified and erect

Question 46

what is the retina?

Answer 46

The inner layer of the back wall of eye is called retina.