Question

A bulb and a capacitor are connected in series to an a.c. source of variable frequency. How will the brightness of the bulb change on increasing the frequency of a.c. source. Give reason.

Answer 1

Dear Student,

Brightness of bulb increases with increase in frequency of ac source current.

$$\begin{gathered} \mathrm{I}=\frac{\mathrm{V}}{\mathrm{Z}}=\frac{\mathrm{V}}{\sqrt{{\mathrm{R}}^2+{\left({\displaystyle \frac{1}{2\mathrm{\pi fC}}}\right)}^2}} \\ \mathrm{where},\mathrm{R}=\mathrm{resistance} \\ \mathrm{f}=\mathrm{frequency} \\ \mathrm{C}=\mathrm{capacitance}\mathrm{of}\mathrm{capacitor} \\ \mathrm{By}\mathrm{increasing}\mathrm{frequency},\mathrm{impedence}\mathrm{decreases},\mathrm{so}\mathrm{current}\mathrm{in}\mathrm{the}\mathrm{bulb}\mathrm{increases}. \end{gathered}$$