Question

light beam produced spectrum in a prism but if we take a rectangular or square glass thing the light cannot show spectrum give reason for it​

Answer 1

In case of prism , after final refraction , the incident ray and the emergent ray makes an angle with the incident ray calledthe angle of deviation . Every colour in the white has different wavelength .The refractive index of prism is different for different colours and therefore different colours deviate through different angles on passing through the prism, Thus , they are seen differently. So, there is dispersion in case of prism.

However, in case of rectangular glass slab , after refraction at the two parallel faces of the glass slab , a ray of light emerges in a direction parallel to the direction of the incidence of white light on the slab. As rays of all colours emerge in the same direction ( of incidence of white light ) , hence there is no dispersion but only lateral displacement.

Hope it helpss….:)