A torch bulb rated as 4.5 W, 1.5 V is connected as shown in the figure. The e.m.f. of the cell needed to make the bulb glow at full intensity is

Current in the bulb =PV=4.51.5=3ACurrent in 1  Ω resistance =1.51=1.5 AHence, total current from the cell, i = 3 + 1.5 = 4.5 ABy using E=V+ir  ⇒  E=1.5+4.5  ×  2.67  =  13.5 V