Two coils are wound on an iron bar, as shown in the figure below.
Coil 1 is connected to a potential difference (p.d.) 
that gives rise to a magnetic field in the iron bar. Coil 2 is now replaced with a copper ring that rests loosely on top of coil 1. The supply to coil 1 is replaced with a cell and a switch that is initially open, as shown in the figure below.
The switch is now closed. As it is closed, the copper ring is observed to jump upwards. Explain why this happens.
Suggest, with a reason, what would be the effect of repeating the procedure in (a) with the terminals of the cell reversed.
