Question

1) Give an detail account on Refraction of light through a Rectangular Glass block with a experiment or a activity.

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Answer 1

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.

Answer 2

Answer!!

Take a rectangular glass block PQRS. A light ray AO falls on the surface PQ. NOM is the normal to the surface PQ at the point of incidence O. At the surface PQ, the ray AO enters from air (rarer medium) to glass (denser medium), so it slows down and bends towards the normal NOM. It travels inside glass in a straight path along OB. At the surface RS, the ray OB suffers another refraction. N₁BM₁ is the normal to the surface RS at the point of incidence B. The ray OB now enters from glass (denser medium) to air (rarer medium), so it speeds up and bends away from the normal N₁BM₁. It travels along BC in air. The ray AP is called the incident ray, OB the refracted ray and BC the emergent ray. The ∠AON is the angle of incidence i, the ∠BOM is the angle of refraction r and the ∠CBM₁ is the angle of emergence e. Since refraction occurs at two parallel surfaces PQ and RS, therefore, ∠MOB = ∠N₁BO and by the principle of reversibility of the path of light ray ∠e = ∠i i.e, the angle of emergence e is equal to the angle of incidence i. Thus, the emergent ray BC is parallel to the incident ray AO. In the figure, we observe that due to the refraction of light at two parallel surfaces of a parallel sided glass block, the angle of emergence is equal to the angle of incidence, so the emergent ray BC and the incident ray AO are parallel, but they are not along the same line. The emergent ray is laterally displaced from the path of the incident ray. The path of the incident ray AO in absence of glass block has been shown by the dotted line OD. The perpendicular distance XY between the path of emergent ray BC and the direction of incident ray OD is called lateral displacement.