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NEET 2009
Exam
NEET
Year
2009
Subject
Physics
Chapter
Magnetic Properties of Matter

NEET 2009 · Physics · Magnetic Properties of Matter

A bar magnet having a magnetic movement of 2 × 10^4 JT^ -1 is free...

A bar magnet having a magnetic movement of 2×104JT−12 \times 10^4 \mathrm{JT}^{-1} is free to rotate in a horizontal plane. A horizontal magnetic field B=6×10−4B=6 \times 10^{-4} TT exists in the space. The work done in taking the magnet slowly from a direction parallel to the field to a direction 60∘60^{\circ} from the field is :

Options

  1. A2 J2 \mathrm{~J}
  2. B0.6 J0.6 \mathrm{~J}
  3. C12 J12 \mathrm{~J}
  4. D6 J6 \mathrm{~J}

Correct answer

D. 6 J6 \mathrm{~J}

Step-by-step solution

W=MB(cos⁡θ1−cos⁡θ2)=2×104×6×10−4(cos⁡θ−cos⁡60∘)=12×12=6J\begin{aligned}\mathrm{W}& =\mathrm{MB}\left(\cos \theta_1-\cos \theta_2\right) \\ & =2 \times10^4 \times6 \times10^{-4}\left(\cos \theta-\cos60^{{}^{\circ}}\right) \\ & =12 \times \frac{1}{2}=6 \mathrm{ J} \end{aligned}
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