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

Answer

D

Explanation

`L=(mu_(0)mu_(r)N^(2)A)/(l)`

`darrI=(E)/(sqrt(omega^(2)L^(2)+R^(2)))=(E)/(sqrt(omega^(2)L^(2)uarr+R^(2)))`
`L prop mu_(r)`
L is increased when iron rod inserted
So current decreased