A monochromatic beam of electrons accelerated by a potential difference V falls normally on the plane containing two narrow slits separated by a distance d. The interference pattern is observed on a screen parallel to the plane of the slits and at a distance of D from the slits. Fringe width is found to be w1. When electron beam is accelerated by the potential difference 4V the fringe width becomes w2. Find the ratio  $\frac{w_1}{w_2}$ (Given d<<D)