Question

Colour spectrum is seen when we look through a muslin cloth why

Answer 1

Muslin cloth is made of very fine threads and as such fine slits are formed. White light passing through these slits gets diffracted giving rise to coloured spectrum. The central maximum is white while the secondary maxima are coloured. This is because the positions of secondary maxima (except central maximum) depend on the wavelength of light. In a coarse cloth, the slits formed between the threads are wider and the diffraction is not so pronounced. Hence no such spectrum is seen.