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Alara1 > Lenses > Flashcards

Lenses Flashcards

1
Q

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

A

it bends TOWARDS the normal

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2
Q

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

A

it moves away from the normal

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3
Q

what is a lens?

A

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)

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4
Q

Convex lens is called _______ why?

A

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

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5
Q

concave lens is called ________

A

diverging lens

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6
Q

convex lens is

A

Thicker in the middle and thinner at the edges

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7
Q

concave lens is

A

thinner in the middle & thicker at the edges

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8
Q

denoted letter and 2nd name of the focal point?

A

(F) principal focus

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9
Q

what is the principal focus?

A

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

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10
Q

focal length?

A

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

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11
Q

The convex lens is called _______ why?

A

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

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12
Q

what is centre of curvature (C)?

A

Centre of a sphere

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13
Q

what is (O)?

A

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

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14
Q

principal axis?

A

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

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15
Q

why is the principal focus of a convex lens real?

A

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

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16
Q

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

A

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

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17
Q

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

A

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

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18
Q

what is rarer medium and denser medium?

A

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

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19
Q

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

A

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

20
Q

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

A

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

21
Q

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

A

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

22
Q

what happens when an image is between O and F?

A

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

23
Q

what is an aperture?

A

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

24
Q

image formation in the camera?

A

pg. 143

25
Q

short-sightedness is also called?

A

Near sightedness myopia

26
Q

which lens is used in myopia?

A

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

27
Q

long-sightedness is also called?

A

far sightedness hyperopia

28
Q

which lens is used in long-sightedness?

A

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.

29
Q

causes of near sightedness?

A

when eye lens becomes much thicker or eyeball become too long

30
Q

causes of long sightedness?

A

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

31
Q

causes of long sightedness?

A

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

32
Q

what is - and + in lens

A

focal length

33
Q

the focal point of a concave lens is ?

A

virtual

34
Q

the focal point of a convex lens is ?

A

real

35
Q

what is a ray diagram?

A

is a drawing showing the path of light rays

36
Q

what part of eye has cells?

A

retina

37
Q

differences of cones and rods?

A

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. |

38
Q

sclera’s properties

A

thick & hard

39
Q

cornea’s properties

A

transparent & hard

40
Q

what happens when you look at a distant object?

A

ciliary muscles relaxed and the lens become thinner

41
Q

what happens when you look at a closer object?

A

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

42
Q

image formation in the concave lens?

A

pg 142

43
Q

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

A

shorter
larger

44
Q

what types of image is formed by a concave lens?

A

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

45
Q

what types of image is formed between O & F?

A

virtual magnified and erect

46
Q

what is the retina?

A

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

Alara1 (5 decks)

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