The YDSE apparatus is as shown in figure. The condition for point P to be a dark fringe is

YDSE set up shown in figure.

YDSE set up shown in figure.

In a YDSE apparatus, we use white light then :

Two charges are placed s shown in figure below. The potential at point P is

In YDSE apparatus shown in figure wavlength of light used is lambda . The screen is moved away form the source with a constant speed v. Initial distance between screen and plane of slits was D. At a point P on the screen the order of fringe will