Question

A glass prism is able to produce a spectrum when white light passes through it but a glass slab does not

Answer 1

A glass prism is able to
produce a spectrum when
white light passes through it
but a glass slab does not . ...
In the case of a prism, the
two interfaces the light ray
has to pass are not parallel to
each each other and are
inclined at an angle.

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Answer 2

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.

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