Question

A light bulb is connected in the circuit shown in Fig. Q 26.9. If we close the switch S, does the bulb brightness increase, decrease or remain the same? Explain why.

Short answer

The brightness increases.

Step-by-step solution

Definition of series and parallel connection

In a series connection, all the components are connected in such a way that the current that flows through them remains constant.

In a parallel connection, all the components are connected in a way that the potential drop across them remains the same.

Determining the change in brightness on closing the switch

When the switch is closed, the combination of the three resistors in parallel decreases, and the current flows in$R_{eq}$ will increase. Also, this combination is in series with the resistance R. So, the current flows in the circuit increases, and as more current flows in the bulb, therefore more brightness.

Thus, the brightness will increase.