REFRACTION
When light travels in the same homogeneous medium it travels along a straight path. However,
when it passes from on transparent medium to another, the direction of its path changes at
the interface of the two media. This is called refraction of light. Light is always took minimum
time path.
The phenomenon of the change in the path of the light as it passes from one transparent
medium to another is called refraction of light. The path along which the light travels in the
first medium is called incident ray and that in the second medium is called refracted ray. The
angles which the incident ray and the refracted ray make with the normal at the surface of
separation are called angle of incidence (i) and angle of refraction (r) respectively.
1) When light ray goes from 2) When light rays go from rarer
denser to rarer medium it to denser medium it bends towards
bends away from normal. the normal.
, Cause of Refraction?
As we know speed of light is different in different media, i.e. more in rarer medium and
comparatively less in denser medium. So, when light enters a denser medium, its speed reduces a
it bends towards the normal and when it enters rarer medium, its speed increases and it bends
away from the normal.
Light is not a single ray, it is treated as extended object.
=refractive index of medium 1
=refractive index of medium 2
medium 1
medium 2
>
In reflection the frequency, speed and wavelength do not change, but phase change ma
occur depending on the nature of reflecting surface.
Intensity may also get changed after reflection.
In refraction, wavelength & velocity of the light changes but frequency remains the same. i
depends only on the source of light.
Intensity of light may changed during refraction.
Colour is a property of frequency. colour will not change during refraction.
Speed of light is different in different medium.
Greater the difference in the speed of light in two media, greater will be the bending o
refracted light
Sair= 3 x m/s Swater= 2.25 x m/s Sglass= 2 x m/s
Glass is optically denser that water and air.
Light travels faster in optically rare medium and travels slower in optically denser medium.
Refractive Index
Refractive index is exclusive property of medium
It is define as the ratio of speed of light in vacuum to the speed of light in that medium.
It is also called bending ability of the medium.
It is inversely proportional to the speed of light in the medium.
The extent of change in direction that takes place in a given pair of media is expressed i
terms of refractive index.
Speed of light in Vacuum
=
Speed of light in Medium
More is the refractive index of the medium, it will be optically denser. For lower refractive
index, medium will be optically rare.
, Relative Refractive Index
When light passes from one medium 1 to another medium 2, the refractive index of
medium 2 with respect to medium 1 is define as the ratio of speed of light in medium1 to
the speed of light in that medium 2.
1
n2 =
Speed of light in Medium 1 1
n2 = 1
Speed of light in Medium 2
1
n2
Speed of light in Glass
n water =
Glass
Speed of light in water
na
air
n glass 1
water
n water n =
air X X glass
air
nw
n water = 1
air
water
water
nair ng
glass
Q-The refractive index of glass is 1.5. find the speed of the
light in the glass.
n= c
v
Note: The absolute refractive index of
any medium can neverbe smaller that 1
Q-The refractive index of diamond is 2.42 and that of glass is 1.52. How much faster does the
light travel in glass than in diamond?
Q- refractive index of water and glass are 4/3 and 3/2 w.r.t. air. Find the refractive index of
glass w.r.t. water.
When light travels in the same homogeneous medium it travels along a straight path. However,
when it passes from on transparent medium to another, the direction of its path changes at
the interface of the two media. This is called refraction of light. Light is always took minimum
time path.
The phenomenon of the change in the path of the light as it passes from one transparent
medium to another is called refraction of light. The path along which the light travels in the
first medium is called incident ray and that in the second medium is called refracted ray. The
angles which the incident ray and the refracted ray make with the normal at the surface of
separation are called angle of incidence (i) and angle of refraction (r) respectively.
1) When light ray goes from 2) When light rays go from rarer
denser to rarer medium it to denser medium it bends towards
bends away from normal. the normal.
, Cause of Refraction?
As we know speed of light is different in different media, i.e. more in rarer medium and
comparatively less in denser medium. So, when light enters a denser medium, its speed reduces a
it bends towards the normal and when it enters rarer medium, its speed increases and it bends
away from the normal.
Light is not a single ray, it is treated as extended object.
=refractive index of medium 1
=refractive index of medium 2
medium 1
medium 2
>
In reflection the frequency, speed and wavelength do not change, but phase change ma
occur depending on the nature of reflecting surface.
Intensity may also get changed after reflection.
In refraction, wavelength & velocity of the light changes but frequency remains the same. i
depends only on the source of light.
Intensity of light may changed during refraction.
Colour is a property of frequency. colour will not change during refraction.
Speed of light is different in different medium.
Greater the difference in the speed of light in two media, greater will be the bending o
refracted light
Sair= 3 x m/s Swater= 2.25 x m/s Sglass= 2 x m/s
Glass is optically denser that water and air.
Light travels faster in optically rare medium and travels slower in optically denser medium.
Refractive Index
Refractive index is exclusive property of medium
It is define as the ratio of speed of light in vacuum to the speed of light in that medium.
It is also called bending ability of the medium.
It is inversely proportional to the speed of light in the medium.
The extent of change in direction that takes place in a given pair of media is expressed i
terms of refractive index.
Speed of light in Vacuum
=
Speed of light in Medium
More is the refractive index of the medium, it will be optically denser. For lower refractive
index, medium will be optically rare.
, Relative Refractive Index
When light passes from one medium 1 to another medium 2, the refractive index of
medium 2 with respect to medium 1 is define as the ratio of speed of light in medium1 to
the speed of light in that medium 2.
1
n2 =
Speed of light in Medium 1 1
n2 = 1
Speed of light in Medium 2
1
n2
Speed of light in Glass
n water =
Glass
Speed of light in water
na
air
n glass 1
water
n water n =
air X X glass
air
nw
n water = 1
air
water
water
nair ng
glass
Q-The refractive index of glass is 1.5. find the speed of the
light in the glass.
n= c
v
Note: The absolute refractive index of
any medium can neverbe smaller that 1
Q-The refractive index of diamond is 2.42 and that of glass is 1.52. How much faster does the
light travel in glass than in diamond?
Q- refractive index of water and glass are 4/3 and 3/2 w.r.t. air. Find the refractive index of
glass w.r.t. water.
