Download 21.2 Electromagnetism

21.2 Electromagnetism
In 1820 Hans Oersted
discovered how
magnetism and
electricity are
connected
______________.
A unit of measure of
magnetic field
strength, the
oersted
_____________,
is
named after him.
21.2 Electromagnetism
Electricity and Magnetism
How can an electric charge create a
magnetic field?
How is an electromagnet controlled?
How do galvanometers, electric motors, and
loud speakers work?
21.2 Electromagnetism
Electricity and Magnetism
Electricity and magnetism are different aspects of
electromagnetic
a single force known as the ________________
force
____________.
charged
• The electric force results from ___________
particles.
• The magnetic force usually results from the
_______________
of _______________
motion
electrons
• in an atom.
21.2 Electromagnetism
Electricity and Magnetism
Magnetic Fields Around Moving Charges
Oersted discovered an important physics
principle…
moving charges create a magnetic field
vibrating
• Moving charges may be the _______________
charges that produce an electromagnetic wave or the
moving charges in a ______________.
wire
circles
• Magnetic field lines form _____________
around a
straight wire carrying a current.
21.2 Electromagnetism
Electricity and Magnetism
right
If you point the thumb of your _________
hand in
the direction of the current, your fingers _________
curl
in the direction of the magnetic field.
Direction of
current
Direction of
electron flow
Current-carrying
wire
Direction of
magnetic field
21.2 Electromagnetism
Electricity and Magnetism
Forces Acting on Moving Charges
A magnetic field exerts a force on a moving
charge.
A charge moving in a magnetic
field is deflected in a direction
perpendicular to both the
________________
field and to the velocity of the
charge.
Force deflecting
the charge
Velocity of
charge
21.2 Electromagnetism
Electricity and Magnetism
Forces Acting on Moving Charges
A magnetic field exerts a force on a moving
charge.
A current-carrying wire in a magnetic field
perpendicular
will be pushed in a direction _____________
to both the field and the direction of the
current.
21.2 Electromagnetism
Electricity and Magnetism
• Reversing the direction of the current will still
cause the wire to be deflected, but in the
opposite
_______________
direction.
• If the current is
parallel
______________
to the
magnetic field, the force
no
is zero and there is ____
deflection.
21.2 Electromagnetism
Solenoids and Electromagnets
loop
If a current-carrying wire has a ________
in it, the
magnetic field in the center of the loop points right
through
to left ____________
the loop.
21.2 Electromagnetism
Solenoids and Electromagnets
coil
Multiple loops in the wire make a __________.
combine
The magnetic fields of the loops ___________
so
that the coiled wire acts like a ______
bar magnet.
21.2 Electromagnetism
Solenoids and Electromagnets
The field through the center of the coil is the
sum
_______
of the fields from all the turns of the wire.
A coil of currentcarrying wire that
produces a magnetic
field is called a
solenoid
______________
21.2 Electromagnetism
Solenoids and Electromagnets
ferromagnetic
If a ________________
material, such as an iron
rod is placed inside the coil of a solenoid, the
increases
strength of the magnetic field ______________.
• The magnetic field produced by
the current causes the iron rod to
become a ____________.
magnet
electromagnet is a
• An ________________
solenoid with a ferromagnetic core.
• The current can be used to turn
the magnetic field ____
on and ____.
off
21.2 Electromagnetism
Solenoids and Electromagnets
The strength of an electromagnet depends on…
current
• the ___________
in the solenoid
• the number of _________
in the coil
loops
• the type of _________
core
The strength of an electromagnet can be
______________
using the following methods…
increased
• Increase the current flowing through the solenoid.
• Increase the number of turns.
easily
• Use cores that are _____________
magnetized.
21.2 Electromagnetism
Electromagnetic Devices
Electromagnets can convert electrical energy into
motion
work
___________
that can do __________.
• Common example: ______________
doorbells
Electromagnetic devices such as
galvanometers, electric motors, and
electrical
loudspeakers change ________________
energy into ______________
energy.
mechanical
21.2 Electromagnetism
Electromagnetic Devices
Galvanometers
A galvanometer is a device that uses a solenoid to
_____________
small amounts of current.
measure
spring
• A solenoid is attached to a ___________
and is free
to rotate about an iron core.
• The solenoid is placed between the
________
poles of two permanent magnets.
• The greater the current, the more
rotates
the solenoid _____________.
21.2 Electromagnetism
Electromagnetic Devices
A galvanometer uses an electromagnet to move a
_____________.
pointer
One common application is in an automobile
gas
gauge
_______
_____________.
The wire is connected
to a ____________
in the gas tank.
sensor
21.2 Electromagnetism
Electromagnetic Devices
Electric Motors
An electric motor is a device that uses an
electromagnet to turn an ____________.
axle
In this motor, a
battery supplies
current to a loop of
wire through the
_______________.
commutator
21.2 Electromagnetism
Electromagnetic Devices
• When current flows through a loop of wire, the field of
pushes
the permanent magnet ___________
one side of the
pulled
loop. The other side of the loop is ____________.
These forces rotate the loop.
21.2 Electromagnetism
Electromagnetic Devices
Loudspeakers
solenoid
A loudspeaker contains a _____________
placed
pole
around one _________
of a permanent magnet.
The current in the wires entering
the loudspeaker changes
direction and
increases or decreases.
21.2 Electromagnetism
Electromagnetic Devices
The magnetic force exerted by the
permanent magnet moves the coil back and
forth.
As the coil moves, it causes a
vibrate
thin membrane to __________,
waves that
producing sound ________
match the original sound.
Electrical energy converts to mechanical energy
21.2 Electromagnetism
Assessment Questions
1. A charged particle is moving across a plane from left to
right as it enters a magnetic field that runs from top to
bottom. How will the motion of the particle be changed as it
enters the magnetic field?
a.
b.
c.
d.
It will accelerate.
It will deflect either up or down on the plane.
It will deflect perpendicular to the plane.
Its motion will not be affected.
Force deflecting
the charge
21.2 Electromagnetism
Assessment Questions
2. Which change will increase the strength of an
electromagnet made by wrapping a conductive
wire around an iron nail?
a.
b.
c.
d.
reversing the direction of current flow
replacing the nail with a wooden dowel
increasing the number of coils of wire around the nail
using a longer nail
21.2 Electromagnetism
Assessment Questions
3. A loudspeaker uses a magnet to cause which
energy conversion?
a.
b.
c.
d.
mechanical energy to magnetic energy
electrical energy to mechanical energy
electrical energy to magnetic energy
mechanical energy to electrical energy
21.2 Electromagnetism
Assessment Questions
4. The motion of an electric charge creates an
electrical field.
True
False
Direction of
current
Direction of
electron flow
Direction of
magnetic field