A coil of inductance 4 H and resistance 80 Ω is in parallel with a 200 Ω resistor of negligible inductance across a 200 V d.c. supply. The switch connecting these to the supply is then opened, the coil and resistor remaining connected together. State, in each case, for an instant immediately before and for one immediately after the opening of the switch: (a) the current through the resistor; (b) the current through the coil; (c) the e.m.f. induced in the coil; and (d) the voltage across the coil. Give rough sketch graphs, with explanatory notes, to show how these four quantities vary with time. Include intervals both before and after the opening of the switch, and mark on the graphs an approximate time scale.

A coil of inductance 4 H and resistance 80 Ω is in parallel with a 200 Ω resistor of negligible inductance across a 200 V d.c.
supply. The switch connecting these to the supply is then opened, the coil and resistor remaining connected together. State, in
each case, for an instant immediately before and for one immediately after the opening of the switch: (a) the current through
the resistor; (b) the current through the coil; (c) the e.m.f. induced in the coil; and (d) the voltage across the coil. Give rough
sketch graphs, with explanatory notes, to show how these four quantities vary with time. Include intervals both before and
after the opening of the switch, and mark on the graphs an approximate time scale.