Boojho made the circuit given in Fig. 14.3 and observed that the bulb did not glow. On Paheli’s suggestion he added one more cell in the circuit. The bulb now glows. Explain.

Initially the bulb was not glowing because one cell was not able to provide sufficient voltage to cause the current to glow the bulb.

When one more cell is added in the circuit the voltage across the circuit doubles and it becomes sufficient to increase the current. This current heat the filament of bulb sufficiently and bulb glows.