(i)
Incident ray, refracted ray and normal drawn at
incident point always lie in the same plane.
(ii)
Snell’s law: For a given colour of light , the
ratio of side of angle of incidence to the sine of angle of refraction is a
constant,
i.e. Sin i/ sin r = 1μ₂ (constant)
This constant 1μ₂ is called refractive index of second
medium with respect to first medium.
Absolute refractive index of a medium is defined as the
ratio so speed of light in free space (vacuum) to that in the given medium.
I.e. absolute refractive index (μ) =
speed of light in vacuum
Speed
of light in the medium
The refractive index of a medium
is different for different colours. The refractive index of a medium decreases
with the increase in wavelength of light. Hence refractive index of a medium is
maximum fro violet colour of light and minimum for red colour of light.
The refractive index of a medium
decreases with the increase in temperature. But this variation is very small.
When a ray of light enters from
one medium to other medium, its frequency and phase do not change but
wavelength and velocity change.
Some illustrations of Refraction
(i)
Bending of a linear object when it is partially
dipped in a liquid inclined to the surface of the liquid.
(ii)
Twinkling of stars.
(iii)
Oval shape of sun in the morning and evening.
(iv)
An object in a denser medium when seen from a
rarer medium appears to be at a smaller distance.
This is way (a) A fish in a pond when viewed from air
appears to be at a smaller depth them actual depth (b) A coin at the base of a
vessel filed with water appears raised.
