How to construct a simple electric current detector using a dry cell, wire, magnetic compass, and other common materials:
- Prepare the Coil: Wrap about ten turns of insulated wire around the cover of a small cardboard box and strip the insulation from the ends of the wire.
- Mount the Box: Place the box on a block of wood and secure it with thumbtacks.
- Create Leads: Bend two paper clips in half and attach them to the thumbtacks, ensuring the wire ends are wrapped around the thumbtacks and the paper clips are slipped underneath before pressing the tacks into the wood. These paper clips will serve as the leads for the circuit.
- Position the Compass: Place a magnetic compass inside the box.
- Connect the Circuit: Connect one wire between a dry cell terminal and a switch terminal. Connect two other wires from the dry cell and the switch to the paper clip leads.
- Test the Detector: Close the switch and observe the magnetic compass needle; it should move. Open and close the switch several times to confirm the effect.
Why it works: When electricity flows through the coil of wire wrapped around the box, it creates a magnetic field around the coil. This magnetic field interacts with the magnetic needle of the compass, causing it to move, thus indicating the presence of an electric current.