Step-by-Step Solution:

1. Gather Materials:
– You need a magnetic compass, an empty matchbox, a battery of two cells, and connecting wires.

2. Prepare the Matchbox:
– Take the empty matchbox and wrap an insulated electric wire around it several times. This wire will act as a coil.

3. Insert a Needle:
– Place a needle inside the matchbox. The needle will act as a magnetic indicator.

4. Connect the Battery:
– Connect one end of the wire wrapped around the matchbox to one terminal of the battery.
– Leave the other end of the wire free.

5. Connect the Second Wire:
– Take another piece of wire and connect one end to the other terminal of the battery.
– The other end of this wire will also be left free.

6. Testing the Circuit:
– To test the electric circuit, momentarily touch the free ends of the two wires together.
– Observe the compass needle; if the needle shows deflection, it indicates that current is flowing through the circuit.

7. Final Setup:
– Your tester is now ready. The deflection of the compass needle is due to the magnetic effect of the electric current flowing through the wire coil.
Explanation:
– The battery provides the electric current.
– The wire wrapped around the matchbox creates a magnetic field when current flows through it.
– The compass needle reacts to this magnetic field, showing deflection when current is present, thus indicating that the circuit is complete.