Question

Two coils P and Q are kept near each other. When current in coil Q increases at the rate 10 $A/s$, the emf in coil P is 12 mV. When current of 1.5 A flows through coil P, the magnetic flux linked with coil Q in mWb is

• A. 0.9
• B. 1.2
• C. 1.5
• D. 1.8

Hint:

Mutual inductance $M$ is the same whether you consider coil P affecting Q or Q affecting P.

Answer 1

The Correct Option is D

Step 1: Formula
Induced EMF $e = M \frac{dI}{dt}$ and Flux $\phi = MI$.

Step 2: Analysis
First, find mutual inductance $M$:
$12 \times 10^{-3} = M \times 10 \implies M = 1.2 \times 10^{-3}$ H.

Step 3: Calculation
Now find flux in coil Q when current in P is 1.5 A:
$\phi = M \times I_p = (1.2 \times 10^{-3}) \times 1.5 = 1.8 \times 10^{-3}$ Wb.

Step 4: Conclusion
Hence, the magnetic flux is 1.8 mWb. Final Answer: (D)