Figure 13 shows some apparatus used by a teacher in a demonstration. The teacher moved the wire upwards between the magnets. The needle on the ammeter deflected to a value of +0.4 mA and then returned to zero. What effect did this demonstrate?

The experiment demonstrates electromagnetic induction. This is the process where a potential difference (voltage) is induced across a conductor when it is exposed to a changing magnetic field. In this case, the wire is moved through the stationary magnetic field, which is equivalent to the magnetic field changing from the wire's perspective. Because the wire is part of a complete circuit, this induced potential difference drives an electric current, which is detected by the ammeter.