# using electromagnetism

## electromagnetic devices

Many common electric devices contain electromagnets. Some examples include hair dryers, fans, CD players, telephones, and doorbells. Most electric devices that have moving parts contain electric motors. You can read below how doorbells and electric motors use electromagnets.

## electromagnets

Solenoids are the basis of electromagnets. An electromagnet is a solenoid wrapped around a bar of iron or other ferromagnetic material (see Figure 25.6). The electromagnetic field of the solenoid magnetizes the iron bar by aligning its magnetic domains. The combined magnetic force of the magnetized iron bar and the wire coil makes an electromagnet very strong. In fact, electromagnets are the strongest magnets made. Some of them are strong enough to lift a train. The maglev train described earlier, in the lesson "Electricity and Magnetism," contains permanent magnets. Strong electromagnets in the track repel the train magnets, causing the train to levitate above the track. Like a solenoid, an electromagnet is stronger if there are more turns in the coil or more current is flowing through it. A bigger bar or one made of material that is easier to magnetize also increases an electromagnets strength. You can see how to make a simple electromagnet at this URL: (4:57). MEDIA Click image to the left or use the URL below. URL:

## electric motors

An electric motor is a device that uses an electromagnet to change electrical energy to kinetic energy. Figure 25.8 shows a simple diagram of an electric motor. The motor contains an electromagnet that is connected to a shaft. When current flows through the motor, the electromagnet turns, causing the shaft to turn as well. The rotating shaft moves other parts of the device. Why does the motors electromagnet turn? Notice that the electromagnet is located between the north and south poles of two permanent magnets. When current flows through the electromagnet, it becomes magnetized, and its poles are repelled by the like poles of the permanent magnets. This causes the electromagnet to turn toward the unlike poles of the permanent magnets. A device called a commutator then changes the direction of the current so the poles of the electromagnet are reversed. The reversed poles are once again repelled by the like poles of the permanent magnets. This causes the electromagnet to continue to turn. These events keep repeating, so the electromagnet rotates continuously. You can make a very simple electric motor with a battery, wire, and magnet following instructions at this URL: .

## how a doorbell works

Figure 25.7 shows a diagram of a simple doorbell. Like most doorbells, it has a button located by the front door. Pressing the button causes two electric contacts to come together and complete an electric circuit. In other words, the button is a switch. The circuit is also connected to a voltage source, an electromagnet, and the clapper of a bell. When current flows through the circuit, the electromagnet turns on, and its magnetic field attracts the clapper. This causes the clapper to hit the bell, making it ring. Because the clapper is part of the circuit, when it moves to strike the bell, it breaks the circuit. Without current flowing through the circuit, the electromagnet turns off. The clapper returns to its original position, which closes the circuit again and turns the electromagnet back on. The electromagnet again attracts the clapper, which hits the bell once more. This sequence of events keeps repeating as long as the button by the front door is being pressed.

## solenoids

A solenoid is a coil of wire with electric current flowing through it, giving it a magnetic field (see Figure 25.5). Recall that current flowing through a straight wire produces a weak electromagnetic field that circles around the wire. Current flowing through a coil of wire, in contrast, produces a magnetic field that has north and south poles like a bar magnet. The magnetic field around a coiled wire is also stronger than the magnetic field around a straight wire because each turn of the wire has its own magnetic field. Adding more turns increases the strength of the field, as does increasing the amount of current flowing through the coil. You can see an actual solenoid with a compass showing its magnetic north pole at this URL: .

## instructional diagrams

In this diagram, a coil of insulated wire is wound around an iron nail. The wire from the nail is connected directly to the positive terminal of a battery at one end, and through a switch to its negative terminal at the other. When the switch is thrown, the wire forms a complete circuit and an electric current flows from the negative terminal through the wire to the positive terminal. The current flowing through the wire produces a magnetic field resembling the field of a bar magnet with the poles alligned with the nail the wire is wrapped around. The iron the nail is made from is ferromagnetic, and the magnetic field generated by the current in the wire causes the magnetic domains in the iron to allign with it. This makes for a stronger magnetic field than the wire would generate on its own. This combination of a wire coiled around a ferromagnetic material is called an electromagnet.

The diagram shows a simple way to make an iron nail become electromagnet. A wire is run from the positive side of a battery then coil around the nail then to the negative side of the battery. As electric current flows through the wire, magnetic field is produced around the coil of wire with the electric current. The coil of wire with electric current flowing through it is called a solenoid. The more turns the coil has, the strong the electromagnetic field will be.

## questions

device that uses an electromagnet to change electrical energy to kinetic energy

``````a. solenoid

b. ferromagnetic material

c. electromagnet

d. bar magnet

-->  e. electric motor

f. shaft

g. commutator
``````

Factors that affect the strength of a solenoids magnetic field include the

``````a. amount of current flowing through the wire.

b. direction in which the current flows.

c. number of turns in the wire.

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

material such as iron that can be magnetized

``````a. solenoid

-->  b. ferromagnetic material

c. electromagnet

d. bar magnet

e. electric motor

f. shaft

g. commutator
``````

In an electromagnet, the solenoid magnetizes the iron bar by

``````a. reversing the direction of the current.

b. repeatedly turning the current on and off.

-->  c. aligning the magnetic domains of the iron.

d. causing electric current to flow through the bar.
``````

part of an electric motor that changes the direction of the current

``````a. solenoid

b. ferromagnetic material

c. electromagnet

d. bar magnet

e. electric motor

f. shaft

-->  g. commutator
``````

What happens when the clapper of an electric doorbell moves to strike the bell?

``````a. The electromagnet turns on.

-->  b. The doorbells circuit is broken.

c. The voltage source causes current to flow.

d. two of the above
``````

When current flows through an electric motor, its electromagnet

``````a. repels the shaft.

-->  b. rotates continuously.

c. controls the commutator.

d. attracts the permanent magnets.
``````

part of an electric motor that is turned by the rotating electromagnet

``````a. solenoid

b. ferromagnetic material

c. electromagnet

d. bar magnet

e. electric motor

-->  f. shaft

g. commutator
``````

solenoid wrapped around a bar of ferromagnetic material

``````a. solenoid

b. ferromagnetic material

-->  c. electromagnet

d. bar magnet

e. electric motor

f. shaft

g. commutator
``````

Why do the poles of the electromagnet in an electric motor keep reversing?

``````a. The shaft keeps rotating.

b. The permanent magnets keep moving.

-->  c. The current keeps changing direction.

d. The voltage source keeps turning off and on.
``````

type of magnet that a solenoid resembles

``````a. solenoid

b. ferromagnetic material

c. electromagnet

-->  d. bar magnet

e. electric motor

f. shaft

g. commutator
``````

coil of wire with electric current flowing through it, giving it a magnetic field

``````-->  a. solenoid

b. ferromagnetic material

c. electromagnet

d. bar magnet

e. electric motor

f. shaft

g. commutator
``````

A coiled wire has a weaker magnetic field than a straight wire.

``````a. true

-->  b. false
``````

An electromagnet is stronger if more current flows through it.

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

b. false
``````

Electromagnets are not as strong as naturally occurring magnets.

``````a. true

-->  b. false
``````

Electric devices that contain electromagnets include hair dryers.

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

b. false
``````

Most electric devices with moving parts contain electric motors.

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

b. false
``````

Each turn of the wire coil of a solenoid has

``````a. current that flows in a different direction.

b. a bar of iron inside of it.

-->  c. its own magnetic field.

d. two of the above
``````

You can increase the magnetic strength of a solenoid by

``````a. decreasing the amount of current flowing through it.

-->  b. increasing the number of turns of wire in the coil.

c. attaching a compass to it.

d. two of the above
``````

An electromagnet is stronger if it uses

``````a. less current.

b. a straight wire instead of a coil.

c. a smaller bar of ferromagnetic material.

-->  d. a ferromagnetic material that is easier to magnetize.
``````

Devices that contain electromagnets include

``````a. fans.

b. telephones.

c. CD players.

-->  d. all of the above
``````

Pressing the button of an electric doorbell causes two electric contacts to come together and

``````a. turn off an electromagnet.

b. push against a bell.

-->  c. complete an electric circuit.

d. turn a shaft.
``````

The electromagnet in an electric motor is located between

``````-->  a. opposite poles of permanent magnets.

b. the commutator and shaft.

c. the voltage source and coil.

d. none of the above
``````

In an electric motor, the shaft and the electromagnet both have

``````a. electrical energy.

-->  b. kinetic energy.

c. a magnetic field.

d. a source of current.
``````

The magnetic field of a solenoid has north and south poles.

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

b. false
``````

An electric motor contains two electromagnets.

``````a. true

-->  b. false
``````

An electromagnet contains a solenoid.

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

b. false
``````

A solenoid has a magnetic field only when current flows through it.

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

b. false
``````

Very few devices contain electromagnetics.

``````a. true

-->  b. false
``````

The clapper of an electric doorbell is an electromagnet.

``````a. true

-->  b. false
``````

When the clapper of a doorbell strikes the bell, it opens an electric circuit.

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

b. false
``````

The electromagnet of an electric motor is connected to a permanent magnet.

``````a. true

-->  b. false
``````

Only the shaft of an electric motor turns when current flows through the motor.

``````a. true

-->  b. false
``````

The poles of the electromagnet in an electric motor keep reversing.

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

b. false
``````

## diagram questions

Which of the following supplies energy?

``````a. Switch

b. Pins

-->  c. Battery cell

d. Nail
``````

How many components make up the electromagnet?

``````-->  a. 3

b. 2

c. 5

d. 4
``````

This is a coil of wire with an electric current flowing through it.

``````a. Doorbell

b. Electromagnet

c. Motor

-->  d. Solenoid
``````

What would happen if the wire was uncoiled from the nail?

``````a. nothing

-->  b. pins would fall back down

c. a fire would start

d. more pins would be picked up
``````

How many poles are there responsible for creating the magnetic field?

``````-->  a. 2

b. 1

c. 3

d. 4
``````

Which term in the image is pointing to the electromagnet?

``````-->  a. Nail

b. Toggle Switch

c. 12 V Lantern Battery

d. Copper Wire
``````

What is the purpose of the copper wire coiling around the nail?

``````a. It serves no purpose

b. To reduce the resistance

-->  c. To form an electromagnet

d. To increase the resistance
``````

In the circuit, what is directly connected to the battery's negative pole through the copper wire?

``````a. Toggle Switch (negative side)

-->  b. Nail

c. The Battery's Positive Pole

d. Toggle Switch (positive side)
``````

What connects the objects in the diagram?

``````a. Lantern Battery

b. Toggle Switch

c. Nail

-->  d. Copper Wire
``````

What is wrapped around the nail?

``````-->  a. copper wire

b. toggle switch

c. lantern battery

d. transistor
``````

Which part is labeled as S?

``````-->  a. Swithc

b. Gong

c. Cable

d. Battery
``````

What will hit the gong if the switch is closed?

``````-->  a. striker

b. contacts

c. spring

d. soft iron armature
``````

What happens when a stronger magnet is put?

``````a. Smaller e.m.f

b. Nothing

-->  c. Bigger e.m.f.

d. Same e.m.f
``````

How many types of magnetic poles are shown?

``````a. 3

b. 4

-->  c. 2

d. 1
``````

What connects the battery with the nail?

``````-->  a. A wire

b. Water

c. Coal

d. Fire
``````

How many poles do batteries have?

``````a. 4

b. 1

c. 3

-->  d. 2
``````

It is the coil of wire with electric current flowing through it, giving it a magnetic field.

``````a. battery

b. electromagnet

-->  c. solenoid

d. wire coil
``````

Where does electricity come out from?

``````a. The nail

-->  b. The positive side

c. The negative side

d. The wire
``````

What connects the iron nail to the battery?

``````-->  a. insulated wire

b. switch

c. Battery

d. Iron nail
``````

What is the coil of insulated wire connected to at the bottom of the iron nail?

``````a. Socket

-->  b. Switch

c. Battery

d. Iron Nail
``````

What would happen if the nail was replaced with a wooden rod?

``````a. It would be a stronger magnet.

b. it would catch fire.

-->  c. It would demagnetize.

d. nothing would change
``````

In this picture what does the orange represent?

``````a. switch

b. cell

c. iron nail

-->  d. coil of insulated wire
``````

What connects the iron nail with the cell?

``````-->  a. Coil of insulated wire

b. Switch

c. Battery

d. Bulb
``````

What is wrapped around an iron nail to power a cell circuit?

``````a. Coil of insulated metal substance

b. Coil of iron

c. Coil of string

-->  d. Coil of insulated wire
``````

How many objects are used in this circuit?

``````a. 3

b. 6

c. 5

-->  d. 4
``````

In this diagram about using electromagnetism, what surrounds itself around the Iron Nail?

``````-->  a. Coil of insulated wire

b. Cell

c. Nail

d. Switch
``````

What type of nail is used in this example?

``````-->  a. Iron Nail

b. Plaster Board Nail

c. Roofing Nail

d. Casing Nail
``````

What connects the battery with the rod?

``````a. Coal

-->  b. Wire

c. Water

d. Sun
``````

What consists one or more electrochemical cells with external connections provided to power electrical devices?

``````-->  a. Battery

b. Wire

c. Rod

d. Device
``````

What connects the iron nail and battery to make the simple electromagnet?

``````a. circuit

-->  b. wire

c. electron

d. magnet
``````

Which structure connects the iron nail to the battery in the diagram shown?

``````-->  a. Coiled Wire

b. Negative Pole

c. Positive Pole

d. Line
``````

In this diagram of using electromagnetism, what sends magnetism through the wire to the iron nail?

``````-->  a. Battery

b. Iron nail

c. Light

d. Coiled wire
``````

What would happen if the wire was uncoiled from the iron nail?

``````a. It would cause a fire

b. it would create a stronger magnet

-->  c. There would be no magnet

d. It would light up
``````

What is wrapped around the iron nail?

``````a. switch

b. cotton

c. plastic

-->  d. insulated wire
``````