Download Chapter 7 Magnetism: Electromagnets

Chapter 7 Magnetism
Lesson 2 – Electromagnets
Main Idea
An electric current produces a magnetic field. Electromagnets are
used in many household appliances.
Vocabulary
o Electromagnet (343) – a coil of wire wrapped around a metal core
such as an iron bar
o Loudspeaker (344) – a device that changes electrical energy into
sound
o Microphone (345) – a device that uses a magnet to convert sound
into electrical signals
What is an electromagnet?
Main Idea
An electric current flowing through a wire produces a magnetic field
around the wire.
Supporting Detail
A. In 1820’s and 1830’s, Michael Faraday and Joseph Henry found:
1. electric currents make magnetic fields
2. magnets could generate or make electric currents
B. When electric current flows through a wire, it creates a magnetic
field
1. Increasing the current makes the magnetic field stronger
2. When you loop wire into a coil, each loop is its own magnetic
force
3. All of the loops push and pull in the same direction
C. An electromagnet is a coil of wire wrapped around an iron core.
1. When electric current flows through the coil, it creates a
magnetic field.
a. The magnetic field causes the particles inside the metal core
to line up
b. The metal core becomes magnetic
2. When the current stops, the metal core is no longer magnetic.
How does a loudspeaker work?
Main Idea
Electromagnets are used in loudspeakers to make sound.
Supporting Detail
A. A loudspeaker is a device that changes electrical energy into
sounds.
1. A loudspeaker has a magnet and electromagnet.
2. A diaphragm (the part of the speaker that creates sound) is
attached to the electromagnet.
3. As electric current flows through the electromagnet, it creates a
magnetic field. The field comes in contact with the magnetic
field of the permanent magnet causing the electromagnet to be
pushed and pulled by the permanent magnet
4. As the electromagnet moved, it causes the diaphragm to move.
5. The motion of the diaphragm creates sound.
B. Telephones rely on electromagnets.
1. Receiver – the receiver works in a similar manner as the
loudspeaker
2. Microphone
a. The microphone (mouth piece) work in the opposite manner
as the receiver.
b. When speak into the receiver, the sound causes the
diaphragm to vibrate.
c. As the diaphragm vibrates, a magnet generates an electrical
signal in a wire connected to the diaphragm
d. The electrical signal is carried through the wires attached to
the telephone lines.
How else are electromagnets used?
Main Idea
Electromagnets are used in many household appliances and toys.
Supporting Detail
A. An electromagnet can be switched on or off by turning the current
on or off.
B. By changing the current, the strength of the electromagnet
becomes stronger or weaker
C. Electromagnets are used in devices from electric guitars to power
generators.
1. They are used in electric motors that power some trains and toy
cars
2. They are used in transformers to increase or decrease the
voltage
D. Operation
1. The current flows when the switch is turned on
2. The flowing current creates a magnetic field around the core.
3. A nearby metal object is repelled by the magnetic force causing
it to move away
4. As the object get far enough away from the magnetic field, it
changes direction and moves toward the field.
5. As the object gets closer to field, it is repelled again
6. The repeat repel and pull action creates motion energy enabling
the object to strike a bell, move a fan blade, or other form of
movement.
7. When the electric current is stopped
a. The magnetic field disappears
b. The object stops being repelled and pulled
c. The motion stops