Question

A prism causes dispersion of white light while a rectangular glass block does not. Explain.

Answer 1

because dispersion of light we can see only transferred with the prism

Answer 2

It is because rectangular glass block acts as a prism and inverted prism kept aside each other . Hence , when white light get inside a prism it deviated into seven colours depending on their wavelength but the inverted prism which kept aside unites the seven colours again into white light .
Hope it helps ......