Question:

A bar magnet has a magnetic moment of $2.5\,JT^{-1}$ and is placed in a magnetic Held of 0.2T. Work done in turning the magnet from parallel to antiparallel position relative to field direction is

Updated On: Jun 23, 2023
  • 0.5 J
  • 1 J
  • 2 J
  • 0 J
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The Correct Option is B

Solution and Explanation

Work done, W = - MB(cos $\theta_2$ - cos $\theta_1$) = - MB(cos 180$\circ$ - cos 0$\circ$) = - MB(-1 - 1) = - MB( - 2) = 2 MB = 2 $\times$ 2.5 $\times$ 0.2 = 1 J
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Notes on Magnetism and matter

Concepts Used:

Magnetism & Matter

Magnets are used in many devices like electric bells, telephones, radio, loudspeakers, motors, fans, screwdrivers, lifting heavy iron loads, super-fast trains, especially in foreign countries, refrigerators, etc.

Magnetite is the world’s first magnet. This is also called a natural magnet.  Though magnets occur naturally, we can also impart magnetic properties to a substance. It would be an artificial magnet in that case.

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Some of the properties of the magnetic field lines are:

  • The lines and continuous and outside the magnet, the field lines originate from the North pole and terminate at the South pole
  • They form closed loops traversing inside the magnet. 
  • But here the lines seem to originate from the South pole and terminate at the North pole to form closed loops.
  • More number of close lines indicate a stronger magnetic field
  • The lines do not intersect each other
  • The tangent drawn at the field line gives the direction of the field at that point.