Question

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

• 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 reactance XC = XL is included in the same circuit.

Answer 1

Answer: (A)

Brightness of the bulb
• decreases when an iron rod is inserted in the coil as impedance of circuit increases.
• increases when frequency of the AC source is decreased as impedance of circuit decreases.
• Increases when number of turns in the coil is reduced as impedance of circuit decreases.
• increases when a capacitance of reactance $X_C=X_L$ is included in the circuit as impedance of circuit decreases