The various devices in which RC and RL circuits find applications and some of these
applications take advantage of the short or long time constants of RC or RL circuits. The circuit in
Figure 1 was used by a biology student to study “frog kick”. She noticed that the frog kicked a little
when the switch was closed but kicked violently for 5 seconds when the switch was opened.
Assume that it takes 10 mA for the frog to kick violently and the frog is modelled as a resistor. (i)
Derive the circuit differential equation for t > 0; (ii) Calculate the frog’s resistance; (iii) Explain
why the frog kicks violently for 5 seconds when the switch was opened.