Objective: Investigation of how the current through a coil changes over time when the DC supply is turned on and off
The behaviour of a coil in a DC circuit changes as soon as the DC supply is turned on or off. The change in current is delayed by self-induction of the coil until it reaches its final value when turning on or zero when turning off. A plot of the coil current against time can be shown to be an exponential curve, i.e. the current through the coil drops by half in the space of a fixed period T1/2 called the half-life. The same period elapses when the current drops from a half to a quarter and from a quarter to an eighth. The half-life period is proportional to the inductance and the resistance of the circuit.