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NEET 2016
Exam
NEET
Year
2016
Subject
Physics
Chapter
Magnetic Effects of Current

NEET 2016 · Physics · Magnetic Effects of Current

A bar magnet is hung by a thin cotton thread in a uniform...

A bar magnet is hung by a thin cotton thread in a uniform horizontal magnetic field and is in equilibrium state. The energy required to rotate it by 60o{60}^{o} is WW. Now, the torque required to keep the magnet in this new position is

Options

  1. AW3\dfrac{W}{\sqrt{3}}
  2. B3W\sqrt{3}W
  3. C3W2\dfrac{\sqrt{3}W}{2}
  4. D2W3\dfrac{2W}{\sqrt{3}}

Correct answer

B. 3W\sqrt{3}W

Step-by-step solution

W=PE(cosθ1−cosθ2)W = PE\left(cos {\theta}_{1} - cos {\theta}_{2}\right)

W=PE(cos⁡0−cos60o)W = PE\left(\cos 0 -cos {60}^{o}\right)

=PE2= \dfrac{PE}{2}.

⇒PE=2W⇒ PE = 2W

τ=PEsinθ=2Wsin60o=3Wτ = PEsin \theta = 2Wsin {60}^{o} = \sqrt{3}W.

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