Question

write any two reasons of Huygens principles in secondary waves​

Answer 1

If the source is very far (i.e. at infinite distance) the wave front is plane. If the source is in form of a slit at a finite distance, the wave front is cylindrical. (ii) Every point of the medium on a given wave front is a centre of originating new disturbance. This new disturbance is called the secondary wavelet.