A glass prism is able to produce a spectrum when white light passes through it but a glass slab does not produce any spectrum. Explain why is it so?
Answers
A glass prism is able to produce a spectrum , which is a patch of light obtained due to dispersion. This is because the opposite refracting faces of a glass prism are not parellal. ... Thus, a rectangular glass slab is unable to produce a spectrum due to the refracting faces being parellal to each other .
Answer:
For dispersion, the two refracting surfaces must be inclined to each other as in case of prism. In rectangular glass slab, the refracting surfaces are parallel to each other. So, dispersion cannot occur. This is due to fact that the rectangular glass slab can be considered as equivalent of two identical prisms in inverted position placed in an inverted position with respect to each other. The deviation and dispersion produced by the second inverted prism is equal and opposite to that produced by the first prism.
Therefore, there will neither be dispersion, nor deviation, Le. second inverted prism recombines the , colour to give a white light parallel to the incident ray again and will undergo only lateral displacement. Hence, rectangular glass slab cannot produce any spectrum.