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Physics > Light and Optics > Flashcards

Light and Optics Flashcards

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1
Q

Why does pencil appear bent in water

A

refraction of light

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2
Q

what happens when light travels from a medium of low optical density to high optical density

A

the light ray bend towards the normal

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3
Q

why does light ray bend towards the normal when it travels from a medium of low optical density to high optical density (2m)

A

the velocity of light decreases when light travels from an optically less dense medium to a denser medium

because of this, the angle of refraction is smaller than angle of incidence

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4
Q

what happens when light travels from a medium of high optical density to low optical density

A

the light ray bends away from the normal

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5
Q

why does light ray bend away from the normal when it travels from a medium of high optical density to low optical density (2m)

A

the velocity of light increases when light travels from an optically less dense to a denser medium

because of this, the angle of refraction is bigger than angle of incidence

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6
Q

what is the formula for refractive index

A

n = (speed of light in vacuum/ speed of light in medium) = c/v

c = 3.0 x 10^8 ms-1

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7
Q

what are the laws of refraction of light

2m

A
  • the incident ray, refracted ray and normal meet at one point and are in the same place
  • snells law: n1 sin θ = n2 sin θ
    n2/n1 = sin θ1/sin θ2
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8
Q

why does an image of a fish appear closer to the water surface

A

refraction of light

light is refracted closer to the normal when air to water
this causes image to be closer

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9
Q

what is the relationship between the refractive index of a medium, real depth and apparent depth

A

n = real depth/ apparent depth = H/h

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10
Q

How does total internal reflection happens

A

it occurs when light travels from a medium of high optical density to low optical density

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11
Q

what happens when incident angle is less than the critical angle

A

the ray is reflected away from the normal

a weak reflected ray can be detected

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12
Q

what happens when the incident angle is the same as the critical angle

A

the refracted ray travels along the medium boundary

the reflected ray appears brighter

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13
Q

what happens when the incident angle is greater than the critical angle

A

no refracted ray

total internal reflection occurs

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14
Q

what is the relationship between critical angle and refractive index

A

n = 1/sin c

the higher the refractive index of a medium, the smaller the critical angle of the medium

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15
Q

what are examples of natural phenomenas that involve total internal reflection

A

formation of rainbow

mirage

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16
Q

how does rainbow occur

A

when light from the sun enters water droplets, the light experiences refraction and disperses into different colors

all these different colors experience total internal reflection on the surface of water droplets

lights rays reflected experience refraction and dispersion again when moving from water to air

colours of the rainbow are seen by the observer

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17
Q

how does mirages occur

A

1) layers of air above the road have different optical densities. The layer of sir just above the road surface is hotter than the upper layers. The layer of hot air has smaller optical density than cold air.
2) light which travels from the upper layer to the lower layer are gradually refracted away from the normal. When the angle of incidence is greater than the critical angle, total internal reflection occurs.
3) reflected light rays are then gradually refracted towards the normal and reach the eyes of the observer. The observer will see the image of a cloud as a puddle of water on the road surface

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18
Q

what are examples of application of total internal reflection in daily life

A

prism periscope

optical fibre

cat’s eye reflector

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19
Q

name two types of lenses

A

convex lenses and concave lenses

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20
Q

what are convex lenses known as

A

converging lenses

21
Q

what are concave lenses known as

A

diverging lenses

22
Q

why are convex lenses called converging lenses

A

because light rays that pass through it converge at focal point

23
Q

why are concave lenses called diverging lenses

A

because light rays appear to be diverging from a focal point

24
Q

what is optical centre

A

point at the centre of the lens. Light rays passing through the optical centre are not reflected

25
Q

what is principal axis

A

straight line through the optical centre of a lens and the centre of curvature of both surface of the lens

26
Q

what is axis of lens

A

straight line through the optical centre and perpendicular to the principal axis

27
Q

what is focal point, F

A

point located at the principal axis of a lens
- for convex lens, light rays parallel to the principal axis will converge at this point after passing through the lens

  • for concave lens, light rays parallel to the principal axis appear to diverge from this point after passing through the lens
28
Q

what is object distance, u

A

distance between object and optical centre of a lens

29
Q

what is image distance, v

A

distance between image and optical centre of a lens

30
Q

what is focal length, f

A

distance between focal point, F and optical centre, O of a lens

31
Q

what is the thin lens formula

A

1/f = 1/u + 1/v

32
Q

what are the conditions for the sign convention to be positive

A

focal length: convex lens

image distance:

  • real image
  • on the opposite side of the project
33
Q

what are the conditions for the sign convention to be negative

A

focal length: concave lens

image distance:

  • virtual image
  • on the same side as the object
34
Q

what is the ray diagram, image position, characteristic of image, when object is at infinity

A

image position:
v = f
image at f

characteristic of image:
real
inverted
diminished

35
Q

what is the ray diagram, image position, characteristic of image, when object O beyond 2F

A

image distance:
f < v < 2f
image between F and 2F

characteristic of image
real
inverted
diminished

36
Q

what is the ray diagram, image position, characteristic of image, when object O at 2F

A

image position:
v = 2f
image at 2f

characteristic of image
real
inverted
same size of object

37
Q

what is the ray diagram, image position, characteristic of image, when object O between F and 2F

A

image position:
v > 2f
image beyond 2F

characteristics of image:
real
inverted
magnified

38
Q

what is the ray diagram, image position, characteristic of image, when object O at F

A

image position:
image at infinity

characteristic of image:
virtual
upright
magnified

39
Q

what is the ray diagram, image position, characteristic of image, when object O between F and optical centre

A

image position
v> u

characteristics of image:
virtual
upright
magnified

40
Q

what is the ray diagram, image position, characteristic of image, when object O beyond 2F in concave lens

A

image position:
between optical centre and focal point
v

41
Q

what is the ray diagram, image position, characteristic of image, when object O between F

A

image position:
between optical centre and focal point
v

42
Q

what is the formula for linear magnification

A

m = v/u = hi/ho

43
Q

how does a gemologist use a magnifying glass

A

identify and evaluate gemstones

44
Q

how does an astronomer use a telescope

A

study celestial objects

45
Q

how does an astronomer use a magnifying glass

A

to examine eyes

46
Q

how does an microbiologist use a microscope

A

to examine various microorganisms

47
Q

how does a geologist use a microscope

A

study and identify specimens of rocks and materials

48
Q

what does a compound microscope made out of

A

two convex lenses with short focal lengths.
Objective lens has focal strength, fo and eyepiece lens has focal strength, fe. Focal strength fo is less than focal strength fe.

Physics (2 decks)

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