9.3.1 Refraction through a Rectangular Glass Slab

. . Refraction through a Rectangular Glass Slab To understand the phenomenon of refraction of light through a glass slab, let us do an Activity. In this Activity, you will note, the light ray has changed its direction at points O and O ′ . Note that both the points O and O ′ lie on surfaces separating two transparent media. Draw a perpendicular NN’ to AB at O and another perpendicular MM ′ to CD at O ′ . The light ray at point O has entered from a rarer medium to a denser medium, that is, from air to glass. Note that the light ray has bent towards the normal. At O ′ , the light ray has entered from glass to air, that is, from a denser medium to a rarer medium. The light here has bent away from the normal. Compare the angle of incidence with the angle of refraction at both refracting surfaces AB and CD. In Fig. . , a ray EO is obliquely incident on surface AB, called incident ray. OO ′ is the refracted ray and O ′ H is the emergent ray. You may observe that the emergent ray is parallel to the direction of the incident ray. Why does it happen so? The extent of bending of the ray of light at the opposite parallel faces AB (air-glass interface) and CD (glass-air interface) of the rectangular glass slab is equal and opposite. This is why the ray emerges parallel to the incident ray. However, the light ray is shifted sideward slightly. What happens when a light ray is incident normally to the interface of two media? Try and find out. Now you are familiar with the refraction of light. Refraction is due to change in the speed of light as it enters from one transparent medium to another. Experiments show that refraction of light occurs according to certain laws.