A student connects a 9 V battery to three identical lamps in series. Each lamp has a potential difference of 3 V across it and a current of 0.2 A flowing through it. Explain how energy is transferred in this circuit, starting from the battery and ending with what happens inside each lamp.

Chemical energy stored in the 9 V battery is converted into electrical energy as the battery’s chemical reactions push electrons through the circuit.

The 9 V potential difference means each electron gains 9 J of energy as it moves from the negative to the positive terminal. In series, the 9 V is divided equally, so each lamp experiences a 3 V drop.

This 3 V drop represents the work done on each electron by the battery as it passes through the lamp’s filament; the current of 0.2 A carries 0.2 C s⁻¹, so the power delivered to each lamp is 3 V × 0.2 A = 0.6 W.

Inside the filament, the electrical energy is converted to thermal energy and light. Electrons collide with the metal ions, increasing the filament’s temperature and causing it to glow, while the rest of the energy is dissipated as heat.

Thus, chemical energy → electrical energy → work on charges → heat and light in the lamps.