21.1 Magnets and Magnetic Fields All magnets have two magnetic poles, regions where the magnet’s force is strongest. One end of a magnet is its north pole

21.1 Magnets and Magnetic Fields

All magnets have two magnetic poles, regions where the magnet’s force is strongest.

• One end of a magnet is its north pole.• The other end is its south pole. • The direction of the magnetic force between two

magnets depends on how the poles face.

Magnetic Forces


A magnetic field surrounds every magnet. Iron filings reveal the field lines, which start near the north pole and extend toward the south pole.

Magnetic Fields

• Where lines are close together, the field is strong. • Where lines are more spread out, the field is weak.


A. When like poles of two magnets come together, the magnets repel each other.

B. When opposite poles of magnets come together, the magnets attract each other.

Magnetic Fields


If you cut a magnet in half, each half will have its own north pole and south pole because the domains will still be aligned.

A magnet can never have just a north pole or just a south pole.

Magnetic Materials


A magnetic field can magnetize ferromagnetic materials. A. Before magnetization, domains are random.

B. Domains aligned with the field grow during magnetization. Unaligned domains can shrink.

Magnetic Materials


Electricity and magnetism are different aspects of a single force known as the electromagnetic force.

• The electric force results from charged particles.

• The magnetic force usually results from the movement of electrons in an atom.

Electricity and Magnetism


Magnetic Fields Around Moving Charges

Moving charges create a magnetic field.• Moving charges may be the vibrating charges that

produce an electromagnetic wave or the moving charges in a wire.

• Magnetic field lines form circles around a straight wire carrying a current.



If you point the thumb of your right hand in the direction of the current, your fingers curve in the direction of the magnetic field.


Direction of electron flow

Direction of current

Current-carrying wire

Direction of magnetic field


A coil of current-carrying wire that produces a magnetic field is called a solenoid.

Solenoids and Electromagnets

The magnetic field lines around a solenoid are like those of a bar magnet.


he strength of an electromagnet can be increased using the following methods.

• Increase the current flowing through the solenoid.

• Increase the number of turns.• Adding a metal core.

Solenoids and Electromagnets


Electric Motors

An electric motor is a device that uses an electromagnet to turn an axle.

Electromagnetic Devices


Assessment Questions

1. Where does the magnetic field of a magnet have the strongest effect on another magnet? a. the north pole

b. the south pole

c. both poles equally

d. midway between the two poles



1. Where does the magnetic field of a magnet have the strongest effect on another magnet? a. the north pole

b. the south pole

c. both poles equally

d. midway between the two poles

ANS: C



2. What happens to a permanent magnet if its magnetic domains lose their alignment? a. The magnetic field reverses direction.

b. It loses its magnetic field.

c. It has several north poles and several south poles.

d. It is no longer a ferromagnetic material.



2. What happens to a permanent magnet if its magnetic domains lose their alignment? a. The magnetic field reverses direction.

b. It loses its magnetic field.

c. It has several north poles and several south poles.

d. It is no longer a ferromagnetic material.

ANS: B



3. Which change will increase the strength of an electromagnet made by wrapping a conductive wire around an iron nail? a. reversing the direction of current flowb. replacing the nail with a wooden dowelc. increasing the number of coils of wire around the naild. using a longer nail



3.Which change will increase the strength of an electromagnet made by wrapping a conductive wire around an iron nail? a. reversing the direction of current flowb. replacing the nail with a wooden dowelc. increasing the number of coils of wire around the naild. using a longer nail

ANS: C

Documents

21.1 Magnets and Magnetic Fields All magnets have two magnetic poles, regions where the magnet’s force is strongest. One end of a magnet is its north pole