Q65 / 120 · NEET 2011 (Mains) · Physics

A short bar magnet of magnetic moment $0.4 \mathrm{~J} \mathrm{~T}^{-1}$ is place in a uniform magnetic field of $0.16 \mathrm{~T}$. The magnet is stable equilibrium when the potential energy is

  • A
    $-0.64 \mathrm{~J}$
  • B
    zero
  • C
    $-0.082 \mathrm{~J}$
  • Correct answer
    D
    $0.064 \mathrm{~J}$

Solution

We know that $U=-M B \cos \theta$ For stable equilibrium $\theta=0^{\circ}$ $\begin{aligned} U & =-M B \\ & =-(0.4)(0.16)=-0.064 \mathrm{~J} \end{aligned}$

Hence, the correct answer is option: 'D'.

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