Question:

A magnet of total magnetic moment $10^{-2} \hat{i} \; A-m^2$ is placed in a time varying magnetic field, $B \hat{i} (\cos t\omega t)$ where $B = 1 $Tesla and $\omega = 0.125 \; rad/s$. The work done for reversing the direction of the magnetic moment at $t = 1$ second, is :

Updated On: Jul 20, 2024
  • 0.007 J
  • 0.02 J
  • 0.01 J
  • 0.028 J
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The Correct Option is B

Solution and Explanation

Work done, $W = ( \Delta \vec{\mu} ) . \vec{B}$
$= 2 \times 10^{-2} \times 1 \; \cos(0.125)$
= $0.02\, J$
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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.

Read More: Magnetism and Matter

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.