Programmes/ Content/ Physics

Refraction at Plane Surfaces

1.The phenomenon of bending of light as it moves from one medium to another is called refraction of light.

2.Those substances which have more density are called denser and which has less density are called rarer.

Laws of Refraction of Light

i. The incident ray, refracted ray and normal at the point of the incident all lie in the same plane.

ii. When light travels from rarer medium to denser medium, it bends towards the normal and when light travels

from denser medium to rarer medium, it bends away from normal.

iii. For given two media, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant,

called refractive index and is denoted by .


where ab is the refractive index of medium b with respect to medium a.

3. When light travels through vacuum to any other medium, the refractive index is called absolute refractive index.

absolute refractive index,=

Relation between Relative Refractive Indices


sin i =constant

4.The perpendicular distance between the direction of incident ray and emergent ray is called the lateral shift.

lateral shift(d)= where t is the thickness of slab and d is lateral shift.

5.When the object in denser medium is viewed from rarer medium (object in water from air ) then the object appears to be in

lesser depth than it actually is.


Apparent shift= Real depth-Apparent depth

6.The angle of incidence in denser medium for which the angle of refraction in rearer medium is 90, is called the critical angle of the medium.


7.If the angle of incidence is greater than critical angle, the light is totally internally reflected in same denser medium which is known as total internal reflection.

Conditions for total internal reflection

i. Object must be in denser medium.

ii. Angle of incidence should be greater than the critical angle.

8.Mirage is an optical illusion produced on desert and coal tarred road during hot summer days.

9.Optical fibers are used to transmit light and communication signals through total internal reflection.

10.The frequency of light doesn't change due to refraction.

11.Image by total internal reflection is more brighter than the image by mirror.

12.Critical angle of a medium depends upon the wavelength of light.

13.In a hot region inferior image is formed and in cold region superior image is formed.

14.Total internal reflection doesn't takes place when the light goes from rarer to denser.

15.Absolute refractive index of a medium cannot be less than 1.

16.The total deviation produced in a glass plate is zero.

17.The height of an object on the ground seen from inside water is seen enlarge.

18.Power of a glass plate is zero.

19.For normal incident snell's law is not valid.

20.In place of mirror prism is used in the Binocular.