Question

Draw a circuit diagram using the dual control switches to light a staircase electric light and explain its working.

Answer 1

Let a switch $$S_1$$ be fitted at the bottom and a switch $$S_2$$ at the top of the staircase. Figure (a) shows the off position of the bulb.
The bulb can now be switched on independently by either the switch $$S_1$$ or the switch $$S_2$$.If the switch $$S_1$$ is operated,the connection 'ab' is changed to 'bc', which completes the circuit and the bulb lights up
Similarly, on operating the switch $$S_2$$ the connection 'bc' changes to 'ba',which again completes the circuit.
Similarly, if the bulb is in on position as shown in fig (b) or (c), one can switch off the bulb either from the switch $$S_1$$ or the switch $$S_2$$