Question

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

Answer 1

We know that Dual control switches are the double pole type switches which are generally used at the top and bottom of a staircase, or sometimes at the opposite ends of a long corridor. With such switches, the appliance such as an electric bulb can be switched ON or OFF from two different places.

Complete answer:
Let us first draw a diagram in which the electric bulb remains OFF.

Figure $(a)$ shows when bulb is OFF. Let ${S_1}$ and ${S_2}$ be the switches and let ${S_1}$ be fitted at the top of the staircase. Now we will understand the working of these dual switches.

Now, we can switched ON the bulb independently either by switch ${S_1}$ and switch ${S_2}$ .If switch ${S_1}$ is operated, then the connection $'ab'$ will be changed to $'bc'$ , and connection will complete and bulb will light ON. The diagram of such circuit is given by

Now, on operating the bulb through switch ${S_2}$ , we need to change the connection from $'bc'$ to $'ba'$ and the circuit will be completed and again the bulb will light ON. For such case, the circuit diagram is shown as:

Hence, circuit diagrams for three cases are shown as $(a)$ for the light bulb OFF and $(b),(c)$ are for when the light bulb is ON.

Note: In a staircase, while going up a person puts ON light bulb by operating switch ${S_1}$ which makes the stable connection as shown in the circuit and bulb lights up, similarly while a person switches for ${S_2}$ same connection stables as shown in circuit, and again the light bulb gets ON.