Question

if the distance between slit is decreases in young's experiment then the angle corresponding to bright fringes will be(smaller /larger/unchanged but the fringes become brighter/unchanged but the fringes become dimmer)

Answer 1

Explanation:

Let's talk about both the cases that happen in Young's double slit experiment; diffraction and interference.

In diffraction slit width matters. When the slits are narrow, any light that passes through them, bends at the corners, hence suffer diffraction. As a result there is considerable overlap of the diffraction patterns and hence wide fringes are observed. But, if the width of slits are increased, most light pass through the slits undiffracted. Hence there is less diffraction. As a result the overlap due to diffraction is less and the fringes become narrow and lesser in number.