Explain the refraction of light through a rectangular glass slab with diagram and start the law of refraction
Answers
Explanation:
Refraction through a rectangular glass slab and principle of reversibility of light:
Consider a rectangular glass slab, as shown in figure. A ray AE is incident on the face PQ at an angle of incidence i. On entering the glass slab, it bends towards normal and travels along EF at an angle of refraction r. The refracted ray EF is incident on face SR at an angle of incidence r’. The emerged ray FD bends away from the normal at an angle of refraction e.
Thus the emergent ray FD is parallel to the incident rays AE, but it has been laterally displaced with respect to the incident ray. There is shift in the path of light on emerging from a refracting medium with parallel faces.
On entering into the glass medium light ray bends towards the normal that is light ray gets refracted on entering the glass medium. After getting refracted this ray now travels through the glass slab and comes out of the glass slab by refraction from the other interface boundary. Since ray goes from glass medium to air it again gets refracted and bends away from normal. The incident ray and the emergent ray are parallel to each other.
i is the angle of incidence, r is the angle of refraction and e is the angle of emergence. Angle of incidence and angle of emergence are equal as emergent ray and incident ray are parallel to each other. When a light ray is incident normally to the interface of two media then there is no bending of light ray and it goes straight through the medium.
Laws of refraction:
(i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
(ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction.
If i is the angle of incidence and r is the angle of refraction, then,
1μ 2 = sin r/sin i
This constant value is called the refractive index of the second medium
with respect to the first.
