Question

A light bulb and an open coil inductor are connected in series across an ac source of variable frequency. How will the glow of the bulb be affected when :
(I) an iron bar is inserted inside the coil, and
(II) the frequency of the source is decreased ?
Justify your answers. Assume that in each above case other factors remain unchanged.

Hint:

Remember the direct dependencies: - Core insertion $\rightarrow L \uparrow \rightarrow X_L \uparrow \rightarrow Z \uparrow \rightarrow I \downarrow \rightarrow \text{Glow } \downarrow$ - Frequency change $\rightarrow f \downarrow \rightarrow X_L \downarrow \rightarrow Z \downarrow \rightarrow I \uparrow \rightarrow \text{Glow } \uparrow$ Always trace your logic sequentially: Parameter $\rightarrow$ Reactance $\rightarrow$ Impedance $\rightarrow$ Current $\rightarrow$ Power/Glow.

Answer 1