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

# Summarizing Torque On a Current Loop

## Summary

• 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.

## Glossary

### motor

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

### meter

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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