Question

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

Answer 1

Dual control switches are the double pole type switches which are generally used at the top and bottom of a staircase, or at the opposite ends of a long corridor, etc. With such switches, the appliance (say, a bulb) can be switched on or off from, two different places.

Figure (a)

Bulb on through switch S₁ 

Figure (b)

Bulb on through switch S₂

Figure (c)

The working and circuits of a dual control switch are illustrated in Fig. a, b, c. Let a switch S₁ be fitted 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 S₁ or the switch S₂ If the switch S₁ is operated, the connection ‘ab’ is changed to ‘bc’, which completes the circuit and the bulb lights up [Figure (b)]. Similarly, on operating the switch S₂, the connection ‘bc’ changes to ‘ba’, which again completes the circuit [Figure (c)].

Similarly, if the bulb is in on position as shown in Figure (b), one can switch off the bulb by changing the connections ‘ab’ to ‘bc’ either by the switch S₁ or the switch S₂.

In a staircase, while going up a person puts on the light by operating the switch S₁ so that the connection ‘ab’ changes to ‘bc’ and makes the current flow in the circuit. On reaching at the top of operates the switch S₂ to put off the light so that the connection ‘cb’ changes to ‘ba’ and the flow of current stops.

The same system is operative when a person puts on light by operating the switch S₂ to change the connection ‘cb’ to ‘ba’ and switch off the light by operating the switch S₁ to change the connection ‘ab’ to ‘bc’.