When current flows through a conductor, it creates a magnetic field around the conductor. A compass needle nearby deflects because it responds to that field.
The diagrams show some equipment that the physicist Ørsted used in an investigation in 1820.
Diagram 1 shows the position of eight compass needles around a wire with no current in the wire.
The compass needles line up with and show the direction of the Earth's magnetic field lines.
Diagram 2 shows the position of the same compass needles when a current is in the wire.
Explain why the compass needles turn when the current is switched on.