Join the free ends of the tester together for a moment. This completes the circuit of the tester and the bulb should glow. However, if the bulb does not glow, it means that the tester is not working. Can you think of the possible reasons? Is it possible that the connections are loose? Or, the bulb is fused? Or, your cells are used up? Check that all the connections are tight. If they are, then replace the bulb with another bulb. Now test if the tester is working or not. If it is still not working then replace the cells with fresh cells.
In this activity, if the bulb does not glow, it means that either the connections of the circuit are loose or the bulb is fused or cells are used up. If the tester is working, it can be used to test the materials, i.e., whether it is a conductor or non-conductor of electricity.