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

Answer

A

Explanation

On inserting in iron rod in the coil, self inductance `L` of the coil increase.
`X_(L) = omega L` increase, `Z = sqrt(R^(2) + omega^(2) L^(2))`, increase
`I_(upsilon) = (E_(upsilon))/(Z)` decrease.
`:.` Brightness of bulb decreases.
Choice (a) is correct.