A teacher demonstrates how a current in a wire creates a magnetic field around the wire. Figure 4 shows the wire passing through a piece of cardboard. The current can be switched on and off. Describe how the teacher can use a plotting compass to demonstrate the magnetic effect of the current in the wire.

A current flowing through a wire creates a circular magnetic field around it. To demonstrate this: 1. Place a plotting compass on the cardboard near the wire. With no current, the compass will point to the Earth's magnetic north. 2. Switch on the current. The compass needle will deflect from its original position and align itself with the magnetic field created by the current. This change in the compass needle's direction when the current is on proves that the current has created a magnetic field.