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?
In a glass slab, both the refracting faces are parallel. Dispersion produced by one face is cancelled by the other face and hence no spectrum is produced. In prism, the two refracting faces are not parallel to each other and hence, dispersion produced at the two faces gets added up producing a spectrum.
