Saturday, January 12, 2013

Torque on a Bar Magnet in a Magnetic Field


Let a bar magnet makes angle θ with magnetic field B and 2l be the length of the bar as show in figure.

Force on N-pole = mB along B and Force on S-pole = mB, opposite to B, since these are the equal and opposite forces they produce torque

ז = force x perpendicular distance. = mB x NA = mB x 2lsinθ therefore ז =MBsinθ

The direction of the torque is perpendicular to the the plain containing M and B, and given by right handed screw rules.

Magnetic dipole moment as the torque acting on a dipole held perpendicular to uniform magnetic field of unit strength

SI unit of M is JT-1

7 comments:

  1. Force on N-pole = mB along B and Force on S-pole = mB, opposite to B..............But why these forces are in opposite directions?

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    Replies
    1. Beacuse Megnetic bar contain two pole north and south

      Delete
  2. Where does 2l goes in the last step?

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  3. Where does 2l goes in the last step?

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