Magnetic Fields and Motors

Electric Motor

We were given the electric motor shown above. It consisted of two magnets at either end of a coil that is free to rotate and attached to a rod connected to the yellow frame. The rod contained a commutator that had two metal strips through which current could be passed through. The commutator is a cylindrical piece metallic piece which has slits, breaking up the current and reversing the direction. This is crucial for the motor to keep running. In an earlier demonstration, we had seen a loop with electric charge going through it would rotate 90 degrees when in a magnetic field, but it would just wobble in that (horizontal) position. This is because there is a net torque of zero because of its position with respect to the magnetic field. Alternating the current allows there to be torque applied continuously.

We made a few observations when experimenting with this motor. Firstly, if we reversed both magnets, the motor turned in opposite direction. Secondly, the speed of the motor was dependent on the voltage applied. The higher the voltage, the faster the motor would spin.

Creating a Simple Motor

In this experiment, we created a simple electric motor based on the principles of the motor we used previously. The materials were enamel coated wire, paper clips, sandpaper, magnets, and tape. We also used a grey power supply to power the motor.

We created "stands" with paper clips taped to a whiteboard. The wire was looped many times leaving two straight ends that sat on the paper clip loops. One end of the wire was sanded all the way around while the other only half way (this served as a commutator). Alligator clips attached to a voltage source were connected to each paper clip. a magnet was placed under the coil and another was placed on top creating a magnetic field. This allowed the coil to spin repeatedly. Unfortunately we had trouble finding the perfect position of the top magnet, therefore we kept moving it around the top on the coil until it began moving freely. The video above shows the demonstration.