Two coils P and Q are placed close to one another, as shown in the figure below.
The current in coil P is constant. An iron rod is inserted into coil P. Explain why, during the time that the rod is moving, there is a reading on the voltmeter connected to coil Q.
The current in coil P is now varied as shown in the figure below.
On the figure below, show the variation with time of the reading of the voltmeter connected to coil Q for time 
to time 
.
