Describe an experiment to show that electricity flows only if the circuit is complete and it does not flow if the circuit is incomplete.
Take two torch bulbs A and B. Connect them to a cell through a switch as shown in fig. The bulbs are said to be in series. Close the switch (i.e., the circuit it completed), you will see that both the bulbs glow.
Now take out the connection of the bulb B as shown in fig. Now close the switch, you will observe that the bulb A does not glow, because the circuit is now incomplete.
Now replace the bulb B by a fused bulb fig. and close the switch. Again you will see that the bulb A does not glow. This is because the circuit being in series, is still incomplete.