Physics » Magnetism » Torque on a Current Loop: Motors and Meters

Summarizing Torque On a Current Loop


  • The torque \(\tau \) on a current-carrying loop of any shape in a uniform magnetic field. is

    \(\tau =\text{NIAB}\phantom{\rule{0.25em}{0ex}}\text{sin}\phantom{\rule{0.25em}{0ex}}\theta ,\)

    where \(N\) is the number of turns, \(I\) is the current, \(A\) is the area of the loop, \(B\) is the magnetic field strength, and \(\theta \) is the angle between the perpendicular to the loop and the magnetic field.



loop of wire in a magnetic field; when current is passed through the loops, the magnetic field exerts torque on the loops, which rotates a shaft; electrical energy is converted to mechanical work in the process


common application of magnetic torque on a current-carrying loop that is very similar in construction to a motor; by design, the torque is proportional to \(I\) and not \(\theta \), so the needle deflection is proportional to the current

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