A coil of self-inductance `L` is connected in series with a bulb `B` and an `AC` source. Brightness of the bulb decreases when

Options

A. number of turns in the coil is reduced
B. a capacitance of reactance `X_(C)=X_(L)` is included in the same circuit
C. an iron rod is inserted in the coil
D. frequency of the AC source is decreased

Answer

D

Explanation

When an iron rod is inserted in the coil, then value of `X_(L)` increases (`X_(L)=omegaL=omega(mu_(0)N^(2)A)/(l)`)
(`thereforeu` (Peameability of soft iron) gt absolute permeability `(mu_(0))`)
In LR series ckt, `I_(V)=(E_(V))/(sqrt(R^(2)+x_(L)^(2)))`