Refraction Of Light at Plane Surfaces

Question 1

define refraction

Answer 1

the change in the direction of the path of light, when it passes from one transparent medium to another transparent medium. it is a surface phenomenon

Question 2

(Willebrod Snell’s laws) what are the laws of refraction

Answer 2

1. the incident ray, refracted ray, and normal at the point of incidence, all lie on the same plane
2. the ratio of the sine of the angle of incidence i andd the sine of angle of refraction r is constant for a given pair of media i.e, mathematically. (the constant is called refractive index)

Question 3

define refractive index

Answer 3

the refractive index of second medium with respect to the first medium is defined as the ratio of the sine of angle of incidence in the first medium to the sine of angle of refraction in second medium

Question 4

relationship bw wavelength and speed of light

Answer 4

directly proportional

Question 5

define absolute refractive index

Answer 5

the refractive index of a medium is defined as the ratio of speed of light in vacuum to speed of light in that medium. (always greater than 1)

Question 6

condition for a light ray to pass undeviated during refraction

Answer 6

1. angle of incidence is 0
2. refractive index of medium 2 = medium 1

Question 7

factors affecting refractive index of a medium

Answer 7

1. nature of medium
2. physical conditions like temperature (inverse)
3. colour of wavelength of light

Question 8

speed of different colours of light

Answer 8

red- maximum speed, least refractive index
violet- least speed, maximum refractive index

Question 9

lateral displacement depends on

Answer 9

1. thickness of block/ medium
2. angle of incidence
3. refractive index of medium
4. wavelength of light used.

Question 10

define prism

Answer 10

a prism is a transparent medium bounded by five plane surfaces with a triangular cross section

Question 11

factors affecting angle of deviation in a prism

Answer 11

1. angle of incidence
2. material of prism
3. angle of prism
4. colour or wavelength of light

Question 12

when is angle of deviation minimum

Answer 12

when angle of incidence is equal to angle of emergence

Question 13

if the prism ABC is equiangular…

Answer 13

for r1=r2, the ray inside the prism is parallel to base

Question 14

dependence of angle of deviation on angle of incidence

Answer 14

as i increases, d decreases till it reaches a minimum value. after the minimum, d goes on increasing as i increases.

Question 15

dependence of angle of deviation of refractive index of prism

Answer 15

higher the RI, higher the deviation. (flint glass has more deviation than crown glass)

Question 16

dependence of angle of deviation on wavelength

Answer 16

more the wavelength, lesser the deviation

Question 17

formula for apparent depth

Answer 17

real depth/ refractive index of medium

Question 18

shift by which object appears to be raised depends on

Answer 18

1. refractive index of medium
2. thickness of denser medium
3. wavelength of incident light (inverse)

Question 19

define critical angle

Answer 19

critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 90 degrees.

Question 20

refractive index of glass with respect to air

Answer 20

1/ refractive index of air with respect to glass
(reciprocal in all cases)

Question 21

relationship between critical angle and refractive index

Answer 21

refractive index of glass= 1/ sin C

Question 22

factors affective critical angle

Answer 22

1. colour/wavelength of light (least for violet, most for red), critical angle increases with wavelength
2. temperature (direct)

Question 23

how is critical angle related to RI

Answer 23

inversely proportional

Question 24

define total internal reflection

Answer 24

when a ray of light travelling in a denser medium, is incident on the surface of the rarer medium at an angle of incidence greater than critical angle for the pair of media, the ray is totally reflected back into the denser medium. it reflects 100% of light unlike plane mirrors.

Question 25

conditions for total internal reflection

Answer 25

1. light must travel from denser to rarer medium
2. angle of incidence must be greater than critical angle for the given pair of media

Question 26

purposes of a total reflecting prism

Answer 26

1. deviate a ray of light through 90 degrees (periscope)
2. deviate a ray of light through 180 degrees (binocular and camera to invert image without loss in intensity)
3. to erect an inverted image without producing deviation in its path (slide projector)

Question 27

consequences of total internal reflection

Answer 27

1. mirage
2. crack in glass shines like a mirror
3. diamond sparkles
4. optical fibre is used to transmit a light signal over a long distance without loss in energy