Question

A closely wound solenoid of 1200 turns and area of cross-section 5 cm\(^2\) carries a current. If the magnetic moment of the solenoid is 1.2 J T\(^{-1}\), then the current through the solenoid is

• A. 2.5 A
• B. 2 A
• C. 3 A
• D. 1.5 A

Hint:

Use \( M = N I A \) to find current when magnetic moment and other parameters are known.

Answer 1

The Correct Option is B

Step 1: Formula for magnetic moment
Magnetic moment \(M\) of a solenoid is: \[ M = N I A, \] where \(N\) = number of turns, \(I\) = current, \(A\) = area.
Step 2: Given values
\(M = 1.2\, J T^{-1}\), \(N = 1200\), \(A = 5\, cm^2 = 5 \times 10^{-4}\, m^2\).
Step 3: Calculate current \(I\)
\[ I = \frac{M}{N A} = \frac{1.2}{1200 \times 5 \times 10^{-4}} = \frac{1.2}{0.6} = 2\, A. \] Step 4: Conclusion
Current through the solenoid is 2 A.