# electromagnet

## easy onoff

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.

## 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 electromagnets strength.

## 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 1.1.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

a solenoid has north and south magnetic poles.

``````-->  a. true

b. false
``````

the lines of magnetic force of an electromagnet run

``````a) from one end of the iron bar to the other.

b) in circles around the middle of the iron bar.

c) from the south pole to the north pole of the electromagnet.

-->  d) two of the above
``````

an electromagnet is stronger if

``````a) the iron bar is bigger.

b) there are more turns in the wire.

c) more current flows through the wire.

-->  d) any of the above
``````

electromagnets are the strongest magnets made.

``````-->  a. true

b. false
``````

## diagram questions

No diagram questions associated with this lesson