Question

A coil has inductive reactance \(3\) H. The ratio of its reactance when it is first connected to an a.c. source and then to d.c. source is

• A. zero
• B. \(3\)
• C. infinite
• D. \(1.5\)

Hint:

For d.c., the frequency is zero, so X_L = 0.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The question speaks of a coil of inductance \(3\) H. The inductive reactance is \(X_L=\omega L=2\pi fL\) in an a.c. circuit. For d.c., the frequency is zero.

Step 2: A.C. source:
\(X_L=2\pi f(3)\), which is a non-zero value.

Step 3: D.C. source:
For d.c., \(f=0\), so \(X_L=0\).

Step 4: Ratio:
\[ \frac{X_L(\text{a.c.})}{X_L(\text{d.c.})}=\frac{2\pi f\cdot3}{0}\to\infty \]
Option (C).

Final Answer:
The d.c. reactance is zero, so the ratio is infinite. \[ \boxed{\infty} \]