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Electromagnet

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Electromagnet

This crane is dangling a big round magnet that has picked up metal car parts in a junk yard. The parts practically leap up to the magnet because it’s so strong. That’s because it’s an electromagnet.

What Is an Electromagnet?

An electromagnet is a solenoid wrapped around a bar of iron or other ferromagnetic material. A solenoid is a coil of wire with electric current flowing through it. This gives the coil north and south magnetic poles and a magnetic field. The magnetic field of the solenoid magnetizes the iron bar by aligning its magnetic domains. You can see this in the Figure below . You can learn how to make an electromagnet at this URL: http://www.youtube.com/watch?v=emlzh9XXWgQ

Strength of an Electromagnet

The combined magnetic force of the magnetized wire coil and iron bar makes an electromagnet very strong. In fact, electromagnets are the strongest magnets made. An electromagnet is stronger if there are more turns in the coil of wire or there is more current flowing through it. A bigger bar or one made of material that is easier to magnetize also increases an electromagnet’s strength. At the following URL, you can see an animation demonstrating how these factors affect the strength of an electromagnet. http://www.schoolphysics.co.uk/animations/Electromagnet/index.html

Easy On and Off

Besides their strength, another pro of electromagnets is the ability to control them by controlling the electric current. Turning the current on or off turns the magnetic field on or off. The amount of current flowing through the coil can also be changed to control the strength of the electromagnet.

Q: Why might it be useful to be able to turn an electromagnet on and off?

A: Look back at the electromagnet hanging from the crane in the opening photo. It is useful to turn on its magnetic field so it can pick up the metal car parts. It is also useful to turn off its magnetic field so it can drop the parts into the train car.

Summary

  • An electromagnet is a solenoid wrapped around a bar of iron or other ferromagnetic material. The magnetic field of the solenoid magnetizes the iron bar.
  • The combined magnetic force of the magnetized wire coil and iron bar makes an electromagnet very strong.
  • Electromagnets can be turned on or off and their strength can be changed by controlling the electric current.

Vocabulary

  • electromagnet : Magnet created by electric current flowing through a coil of wire that is wrapped around a bar of iron or other ferromagnetic material.

Practice

Experiment with the electromagnet simulation at the following URL. Then fill in the blanks in the sentences below. http://phet.colorado.edu/en/simulation/magnets-and-electromagnets

  1. Increasing the number of loops in the wire coil __________ the strength of the magnetic field.
  2. Decreasing the voltage of the direct current __________ the strength of the magnetic field.
  3. Each time the alternating current changes direction, the magnetic field __________.
  4. When the amplitude of the alternating current is greater, the strength of the magnetic field is __________.
  5. The more quickly the alternating current changes direction, the more quickly the magnetic field __________.

Review

  1. What is an electromagnet?
  2. How could you increase the strength of an electromagnet?
  3. Why are electromagnets the strongest of all magnets?
  4. How could the crane operator in the opening photo cause the electromagnet to drop the metal parts into the train car?

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