When the light source is kept 20 cm away from a photo cell, stopping potential 0.6 V is obtained. When source is kept 40 cm away, the stopping potential will be
(a) 0.3 V (b) 0.6 V
(c) 1.2 V (d) 2.4 V
(b) Stopping potential does not depend on the relative distance between the source and the cell.