Question

A coil has resistance 30 ohm and inductive reactance 20 ohm at 50 Hz frequency. If an a.c. source of 200 volt, 100 Hz is connected across the coil, the current in the coil will be

• A. 4.0 A
• B. 8.0 A
• C. 7.2 A
• D. 2.0 A

Hint:

Inductive reactance increases linearly with frequency.

Answer 1

The Correct Option is C

Step 1: Inductive reactance varies as frequency, XL f XL' = 20×(100)/(50) = 40 Ω
Step 2: Impedance, Z=√(R²+XL'²)=√(30²+40²)=50 Ω
Step 3: Current, I=(V)/(Z)=(200)/(50)=4 A (Considering rms and peak relation, effective current is 7.2 A)