Electromagnets at Work

1. Electromagnets at Work

2. Background Information • An electromagnet consists of wire coiled around a solid core material, usually iron. The wire coil, or solenoid, generates a magnetic field when electricity is passed through it. This magnetic field acts on the core material, producing microscopic changes that greatly increase the magnetism of the wire coil. Changing the core material or the number of coils can modify the magnetic field that is induced. The best core material is magnetic material such as iron. A magnetic field generated by an electromagnet disappears when the electricity is turned off, making electromagnets extremely useful devices. Electromagnets are used in relays and circuit breakers, in certain brakes and clutches, and to lift and move metal parts and scrap metal.

3. Getting Started • In the last lesson you discovered that current electricity flowing through a wire creates a magnetic force. You also experimented to learn that you could make a temporary magnet by using an electrically charged wire that is coiled around a conductor. The simple idea of creating a temporary magnet has helped develop a wide range of technologies, which have improved our lives in countless ways.

4. These all use electromagnets!

5. Lifting and Driving • Electromagnets are used in places like scrap yards where temporary magnets are used to move large objects that are made of metal. These machines have a large disc made of a conductive material like iron that is attached to a crane arm. The crane operator lowers the disc into a pile of scrap metal or onto a large item like a demolished car. The operator turns on the electricity, which flows to the disc and creates a magnet. The scrap material is then attracted and sticks to the crane, and the operator can move the material to a new location. This way, large objects or a lot of small objects can be moved easily from one place to another.

6. Lifting and Driving • Electromagnets are not only used to pick up and move things. They can be used to create movement that can be harnessed by machines and equipment we use every day. Most electrical items that we use have motors in them. We know that electricity is used to power the motors, but how do the motors create motion?

7. Motion in Motors • The ideas for the first electric motor were developed by Michael Faraday in 1831. Faraday figured out how to force an electromagnet to rotate. These ideas still apply to modern motors. • To answer the question about how motors create motion, think about the electromagnet you made. When you charged the wire coils around the nail, you created an electromagnet with a north and south pole just like the poles on a regular magnet.

8. Motion in Motors • Remember the rule that applies to all magnets – opposite poles attract. The north and south poles you created are attracted to their opposites, so by placing a permanent magnet around the electromagnet you can force which way the electromagnet (the nail) faces. The poles on the permanent magnet strongly attract the opposite poles on the electromagnet, and the magnetic force causes the nail to move.

9. Motion in Motors • Once the poles of the surrounding permanent magnet and electromagnet inside are lined up, how do you get the motor to continue to move? You need a part called a commutator, which switches the poles of the electromagnet by changing the direction of the electrical current. • When the poles of the electromagnet are changed, magnetic force acts again by pushing away from the permanent magnet until the poles of the electromagnet are again facing their opposites.

10. Motion in Motors • As long as electricity continues to flow in alternating directions through the electromagnet, this rotation will continue. • To use the motion of the electromagnet to drive a machine, the motor is connected to an arm that moves with the electromagnet. This arm mimics the motion of the electromagnet and will rotate as long as the motor is on.

11. Motion in Motors • There are many different motors that you can find in your daily life. Anything that plugs in or has a battery, and has motion, will have a motor. In your home you may have everything from fans in your computer to electric toothbrushes in your bathroom. In your school you have items like the recess bell or the clock on the wall. Many items have more than one motor. For example, a DVD player has one motor to spin the disc and another to move the laser that reads the data encoding the movie.

12. K(know), W(want), F(feel) Procedure • First think about what you already know about electromagnets . Then fill it in. Reflect back to what you learned last class. • Next, think about what questions you still have. Do you have any questions about electromagnets at work? • Write down what you learned about uses of electromagnets and the way that motors create motion.

13. References • Johanson, T., Mohr, P., Treptau, C., Wallace, C., Ted, V., et al. (2009). Pearson, Saskatchewan Science 6: Teachers Resource. Toronto: McAlpine, R. • Johanson, T., Mohr, P., Treptau, C., Wallace, C., Ted, V., et al. (2009). Pearson, Saskatchewan Science 6. McAlpine, R.