DC motors

A DC (direct current) motor converts electrical energy into kinetic energy by using the magnetic force of a magnet on a current carrying wire. They are used in a wide variety of applications where rotational motion is required such as toy cars, household appliances such as electric toothbrushes, dishwashers and refrigerators, electric drills and industrial machinery.

Click on the hotspot below to explore the design and operation of a DC motor.

The size of the force on each side of the loop can be determined:

\[F=nIlB\]

From this we can see that in order to increase the force on the wire, and hence the speed of the motor we could increase:

  • \(n\) the number of loops in the coil
  • \(I\) the size of the current in the coil \((A)\)
  • \(l\) the length of the side of the wire parallel to the magnetics \((m)\)
  • \(B\) the strength of the magnetic field \((T)\)

Worked Example

A DC motor is set up with a single square loop of side lengths \(5cm\) to be rotated in between two magnets producing a field of \(4\times10^{-3}T\). A current of \(6mA\) runs through the loop. Determine the size of the force on the sides of the loop.\[F=nIlB=(1)(0.006)(0.05)(4\times10^{-3})=1.2\times10^{-6}N\]