Light-Refraction

Question 1

define refraction

Answer 1

The bending of light rays when they pass obliquely from one medium to another medium is called refraction of light.

Question 2

what is the cause of refraction

Answer 2

Refraction is caused due to the change in speed of light when it enters from one medium to another

Question 3

give the lws of refraction

Answer 3

i)the incident ray, the refracted ray and the normal to the interface to the interface of the two transparent media at the point of incidence all lie in the same plane.

ii) the ratio of the sine of the angle of incidence to the sine of the angle of reflection is a constant, for the light of a given colour and for a given pair of media. this is also known as snell’s law of refraction. it is also the refractive index of the second medium with respect to the first.
n=sin i/sin r

Question 4

what happens when the light ray passes from a rarer medium to a denser medium

Answer 4

the light ray bends towards the normal.
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Question 5

what happens when the light ray passes from a denser medium to a rarer medium

Answer 5

the light ray bends away from the normal.
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Question 6

what is the incident ray

Answer 6

A ray of light falling on the surface separating two mediums is the incident ray.

Question 7

what is the refracted ray

Answer 7

A ray of light traveling in another medium, with change in direction is the refracted ray.

Question 8

what is the emergent ray

Answer 8

the refracted ray which emerges out from a medium after refraction is called emergent ray.

Question 9

in a rectangular glass slab, why is the incident ray parallel to the emergent ray?

Answer 9

the extent of bending of light at the opposite parallel faces of the rectangular glass slab are equal and opposite, so the rays are parallel.

Question 10

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Answer 10

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Question 11

what is lateral displacement

Answer 11

The perpendicular distance between the original path of incident ray and the emergent ray coming out of glass slab is called lateral shift or lateral displacement of the emergent ray of light.

Question 12

give the factors on which lateral shift depends on

Answer 12

-Directly proportional to the thickness of glass slab.
-Directly proportional to incident angle.
- Directly proportional to the refractive index
of glass slab.
-Inversely proportional to the wavelength of light

Question 13

define refractive index

Answer 13

refractive index of a medium is the measure of the change in speed of light when it enters that medium

Question 14

define absolute refractice index

Answer 14

absolute refractive index of a medium is the ratio of the speed of light in air to the speed of light in that medium.
it is denoted by (n)
n=c/v
c=speed of light in air
v=speed of light in medium

Question 15

why is absolute refractive index never greater than 1

Answer 15

Since c > v, therefore absolute refractive index (n) of a medium is always greater than unity (i.e. 1)Refractive index is a pure number. It has no unit.

Question 16

define relative refractive index

Answer 16

relative refractive index of medium 2 to medium 1 is the ratio of the speed of light in medium 1 to speed of lighr medium 2

Question 17

give the factors on whcih refractive index depends on

Answer 17

Nature of material of the medium
Density of the medium
Colour of wavelength of light

Question 18

define lens

Answer 18

Lens is a transparent material bound by two surfaces, of which one or both surfaces are spherical.

Question 19

define convex lens

Answer 19

A lens having both spherical surfaces or one spherical surface and other plane surface such that it is thick in the middle and thin at the edges is known as convex lens.

Question 20

define concave lens

Answer 20

A lens having both spherical surfaces or one spherical and other plane surface such that it is thin in middle and thick at the edges is known as concave lens.

Question 21

define principal axis of lens

Answer 21

an imaginary straight line passing through the centres of curvature of the spherical surfaces forming the lens is called principal axis

Question 22

define optical centre of the lens

Answer 22

the central point of the lens through which the light rays pass undeviated is called the optical centre. it is denoted by “O”

Question 23

define aperture of lens

Answer 23

the effective diameter of the spherical outline of the lens is called aperture

Question 24

define principal focus

Answer 24

a point on the principal axis where all the rays parallel to the principal axis meet or appear to meet after refraction is called principal focus

Question 25

give the rules for the rules of image formation by convex lens

Answer 25

i) a ray of light parallel to the principal axis after refraction passes through the focus of the lens
ii) the ray of light passing through the optical centre of the lens after refraction continues its path without deviation.
iii)the ray of light passing through the focus of the lens after refractions moves parallel to the principal axis.

Question 26

give the rules for the image formation by concave lens

Answer 26

i) the ray of light parallel to the principal axis aafter refraction diverges and appears to come fromt he focus.
ii) the ray of light passing through the optical centre after refraction continues its path without any deviation.
iii)the ray of light which is directed towards the focus of the lens after refractiosn moves parallel to the principal axis.

Question 27

define lens formula

Answer 27

the relation between the focal length, image distance and object distance is given by the lens formula

Question 28

define power

Answer 28

power of a lens can be defined as the reciprocal of its focal lenght. it gives the degree of convergence or divergence achieved by the lens.its is the ability of a lens to converge or diverge the rays of light falling on it

Question 29

define 1 D

Answer 29

1 Dioptre is the power of the lens of of focal length of 1m