Chapter 8Magnets

BIG IDEA: A magnet is surrounded by a magnetic field that exerts a force on other

magnets.

Section 1: SCSh 1a-b, 3c, 3e-f, 4a, 9c, SPS 10c

Section 2: SCSh 9c, SPS 10c

Section 3: SCSh 9c, SPS 10b

GPS Standards: 17.6 = Illustrates the interactions of electricity and magnetism by using electricity to create a magnetic field and magnetic induction to create an electric field.17.7 = Describe the interplay of electric and magnetic forces as the basis for electricity.

All magnets have the following ___________ properties:

Magnets always have two opposite “_______,” called _________ and _______.

If _________, each part of a magnet has both north and south poles; we _______ see an unpaired north or south pole.

When near each other, ________ exert magnetic __________ on each other.

The __________ between magnets depend on the alignment of the poles; _______ unlike poles will ____________ each other and two like poles will ___________ each other.

____________________

Magnet________________

MagnetElectromagnet

MAIN IDEA: ________________________________________________________________________________________________________________________________________________________________________________________________________

In _______, cobalt, nickel and a few other metals the atoms exert a _______ on the other atoms around them.Because of these forces, _______ groups of atoms align their magnetic poles so that almost all like poles point in the ________ direction.

The groups of atoms with aligned magnetic poles are called magnetic ___________.

QUESTION? How do magnetic poles interact with each other?

ANSWER: ________________________________________________________________________________________________________________________________________________________________________________________________

A _________ needle is a magnet that is free to _______ until it lines up in the north-south direction. The origin of the terms “________ pole” and “_______ pole” of a magnet come from the direction that a magnetized compass _______ points. The end of the magnet that pointed ________ was called the north pole of the magnet and the end that pointed ________ was called the south pole.

History of Magnetism

First magnetic metal found: ___________________

(2500 yrs ago in current Turkey)

Greeks called it “Lodestone” or

“Magnesia” = _____________________

First compass used:_______________

(in the twelfth century)

Chinese sailors used a compass made of ________________

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Name three types of magnets:

1. _______________________________________

2. _______________________________________

3. _______________________________________

Two historic discovery places regarding magnets and their importance:

1. _______________________________________

2. _______________________________________

If a magnetic material were melted, would it continue to be magnetic, why? (hint: magnetic domain)

1. _______________________________________

The _________ force depended on the __________ and ___________ of the two magnets and also on the ____________ between them. The model of a magnetic ________ was developed to describe how a magnet exerts magnetic _______.

First, every ________ creates an energy field, called the magnetic ________, in the space around it.

Second, the _________ exerts _____ on any other magnet that is within its range.

QUESTION? What does the force between two magnets depend on?

ANSWER: (Page 224)

____________________________________________________________________________________________________________________________________________________________________________________

Electromagnets = A ________ that is created by _______ current. This type of ______ is called an electromagnet.

A single wire wrapped into a coil around a core is called a _______________.

KNOW: The more current would make an electromagnet stronger. 2 ways to increase the current.

apply more ________ = by adding a second battery. add more _________ = of wire around the nail.

The second method works because the ___________ in the electromagnet comes from the total amount of current flowing around the _____. If there is 1 amp of _____ in the wire, each loop of wire adds 1 amp to the total amount that flows around the ______. Ten loops of 1 amp each make _____ total amps flowing around. By adding more turns, the same __________ is used over & over to get stronger _______________.

Wrap the _______ in many turns around the _____ and connect a ________. When current flows in the ______, the nail becomes a _________. To ______ north and south, reverse the connection to the ________, making the current flow the opposite ________.

BY ADDING MORE __________ THE RESISTANCE OF THE COIL IS ALSO INCREASED. _______________ THE RESISTANCE MAKES THE CURRENT A LITTLE ___________ & GENERATES MORE __________.

A GOOD ELECTROMAGNET IS A ____________ BETWEEN TOO MUCH RESISTANCE AND HAVING ENOUGH _________ TO GET A STRONG ENOUGH __________.

Of course, nothing comes for free.

The magnetic _______ exerted by an electromagnet depends on ____ factors:

The amount of electric ______ in the wire. CURRENT ↑ then MAGNETIC FORCE ↑

The amount of iron or steel in the electromagnet’s ____________. METAL ↑ then MAGNETIC FORCE ↑

The number of __________ in the solenoid.COILS ↑ then MAGNETIC FORCE ↑

Electric motors convert ________ energy into mechanical energy.

Permanent magnets and electromagnets can work together to make _________ motors and generators. The secret is in the ability of an electromagnet to ________ from north to south. By changing the __________ of electric current, the electromagnet changes from attract to repel, and spins the ____________.

QUESTION? Why is it necessary to continually reverse the direction of the current flow in the coil of an electric motor?

ANSWER: (page 236-237) When the end of the coil move past a pole of the permanent magnet, reversing the current causes the end of the coil to be attracted to the other (next) pole of the permanent magnet.

All electric _________ must have ________ things to work:

1. A rotating element (_________) with magnets.

2. A stationary ___________ that surrounds the rotor.

3. A ______________ that switches the electromagnets from north to south at the right place to keep the rotor spinning.

The electromagnet must switch from north to south as each ________ magnet passes by to keep the rotor turning. The switch that makes this happen is called a __________________.

Both electrical _______ and magnetic _________exist between electric charges. Scientists now believe both forces are ______ aspects of _______ force, the electromagnetic _______________.

A _________ through a wire creates a magnet. The reverse is also true: If a _________ is moved through a coil of wire, then electric ______________ is created.

This _________ is called electromagnetic induction because a moving magnet induces electric ____________ to flow.

MAIN IDEA: ________________________________________________________________________________________________________________________________________________________________________________________________________.

When a _________ moves into a coil of wire, it induces electric current to flow in the ________. The current ________ if the magnet ________ moving. If the magnet is pulled back _______ again, the current flows in the opposite direction. A changing magnetic

____________ is what makes the electricity flow.

Electromagnetic _____________ enables us to transform mechanical energy (moving magnets) into __________ energy. Any machine that causes magnets to move past wire coils generates electric currents. These machines include giant electric __________ plants and computer ________ drives.

Power plants use electromagnetic induction to create _________. A generator is a combination of mechanical and electrical systems that converts _________ energy into electrical ____________.

A power plant ____________ contains a turbine that turns magnets inside loops of _________, generating electricity.

In the top sketch the north pole on the disk induces a south pole in the _________________, causing current to flow one way. When the disk rotates, the ____________ in the coil is reversed, and the electric current generated also reverses. THIS IS ALTERNATING CURRENT (_____)

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Name three things a motor requires:

1. _______________________________________

2. _______________________________________

3. _______________________________________

Two forces combine to produce electromagnetic forces:

1. _______________________________________

2. _______________________________________

How does electromagnetic induction generate electricity (AC)

1. _______________________________________

Explain how a magnet exerts a force.

____________________________________________________________________________________________________

Describe the magnetic field produced by an electric current.

_________________________________________________________________________________________________________

Explain how a electromagnet produced a magnetic field.

__________________________________________________________________________________________________________________________________________

Explain how an electric motor operates.

__________________________________________________________________________________________________________________________________________

Describe how a generator produces an electric current. __________________________________________________________________________________________________________________________________________