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Question 20229
JEE Physics · Hard

Magnetism: Force Between Magnetic Dipoles MCQ

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Force Between Magnetic DipolesHardQuestion 20229

Question

Two identical bar magnets are placed coaxially end-to-end (north of one facing south of the other) at separation r. The force between them varies as:
  1. A
    1/r²
  2. B
    1/r³
  3. C
    1/r⁴
    Correct
  4. D
    1/r

Correct answer

1/r⁴

Explanation

Force between magnetic dipoles = gradient of energy. Energy U ∝ 1/r³ (dipole field), so F = −dU/dr ∝ 1/r⁴.

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