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JEE Main 2021 (26 Aug, Shift 1) · Field of a Magnet & Magnet in a Uniform Field

Field of a Magnet & Magnet in a Uniform Field question from JEE Main 2021 (26 Aug, Shift 1)

Q13JEE Main 2021 · 26 AUG · SHIFT 1Difficult

Field of a Magnet & Magnet in a Uniform Field

Two short magnetic dipoles m1 and m2 each having magnetic moment of 1 Am2 are placed at point O and P respectively. The distance between OP is 1 meter. The torque experienced by the magnetic dipole m2 due to the presence of m1 is ........... ×\times 10−-7 Nm.

Figure

Numerical answer type. Work it out, then open the answer.

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Answer: 1

  1. P is on the equatorial line of m1m_1 (which points up), so B1=μ04πm1r3B_1 = \frac{\mu_0}{4\pi}\frac{m_1}{r^3}, pointing down.
  2. B1=10−7×113=10−7 TB_1 = 10^{-7} \times \frac{1}{1^3} = 10^{-7}\ \text{T}
  3. m2m_2 points right, perpendicular to B1B_1: τ=m2B1sin⁡90∘=1×10−7 N m\tau = m_2B_1\sin 90^\circ = 1 \times 10^{-7}\ \text{N m}
  4. So the answer is 1.
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