A Simple DC Motor & Review of Electromagnetism
Physics of the Mundane
Adam Johnston
In playing with batteries, magnets, and a variety of other things, you have basically witnessed the following rules of nature:
| An electric current (moving electric charge) will produce magnetic forces. You witnessed this when wires of current deflected a compass needle. |
| A changing magnetic force will induce an electric current. You witnessed this by moving a magnet through a coil of wire that was connected to a current meter. |
A variety of other demonstrations can show these fundamental ideas as well. In fact, these basic ideas are what allow us to produce electricity and are also what allow us to create motors. The latter is what you will build. You should have
| Some shiny, insulated copper wire (about 1.5 m long) |
| A D-cell battery |
| Some paper clips |
| A rubber band |
| A cup or other stand to mount your motor to |
| Some sandpaper |
Procedure:
| Coil the wire around your D-cell battery until you have a tightly wound set of loops (with about 10-15 coils in it). Each end of the wire should wrap around the coils on each side and extend outward to form an axis. See your instructor’s model to get a good picture of this. |
| On one of the wire ends, sand the insulation off completely. On the other end, sand off ONLY HALF of the insulation. That is, you will sand on the entire length of this end, but only on the top (or bottom) half of the wire. Again, see your instructor’s model. |
| Tape your D-cell to the top of a cup so that the battery is lying horizontally. |
| Unbend 2 paper clips so that they look like an “S”. Then, bend the top part of this “S” backwards so that it provides a small valley/cradle that the ends of your copper coil will rest in. Your instructor has a model of this as well. |
| Attach the paper clips to the battery using a rubber band. Each end of the battery should have a modified paper clip attached to it, pointing the modified end upwards. The paper clips should extend upwards high enough that the coil of wire can rest on the paper clips and be able to spin freely. “Stick” a magnet to the battery, in between the battery and the coil of wire, and make adjustments to the paperclips and coil as necessary. |
| Now play with your contraption. Realize that when you lay the copper coil across the two paper clips it will begin to draw current from your battery. If it is not doing anything else, it will get very hot and drain your battery quickly. |
Questions:
| How does your contraption – what should be a small motor – work? Where are the forces coming from? Why is the battery required? |
| Why do you need to sand only HALF of the insulation from one end of the coil? |
| How does conservation of energy apply to this motor? In other words, where does the energy of this motor come from? |