Physics · Ampere's law and its applications to infinitely long current carrying straight wire and solenoid
Assertion If the current in a solenoid is reversed in direction while keeping th
Assertion If the current in a solenoid is reversed in direction while keeping the same magnitude, the magnetic field energy stored in the solenoid decreases. Reason Magnetic field energy density is proportional to square of current
- A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
- B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
- C. Assertion is correct but Reason is incorrect
- D. Assertion is incorrect but Reason is correct
Step-by-step solution
The magnetic field energy in a solenoid is U = (1/2) L I^2, which depends only on the magnitude of current, not direction. Reversing current at same magnitude does not change energy, so assertion is false. The reason correctly states that energy density is proportional to the square of current (since B ∝ I).
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