Question

A straight line conductor of length 0.4 m is moved with a speed of \(7.0\text{ ms}^{-1}\) perpendicular to magnetic field of intensity \(0.8\text{ Wb m}^{-2}\). The induced e.m.f. across the conductor is

• A. \(2\cdot 24\) V
• B. \(2\cdot 80\) V
• C. \(3\cdot 20\) V
• D. \(5\cdot 60\) V

Hint:

Self-inductance goes as N squared times area over length.

Answer 1

The Correct Option is A

Step 1: Scaling:
If both the radius and the length are multiplied by 3, $r^2$ becomes 9 times and $l$ becomes 3 times, so L is multiplied by $\frac93 = 3$.

Step 2: Result:
B has 3 times the inductance of A, so $L_A : L_B = 1 : 3$ (B).

Final Answer:
1 : 3. \[ \boxed{1 : 3} \]