# Chapter 24 Physics: Magnetism

The source of all magnetism is

moving electric charge.

The force that acts between a pair of magnetic poles depends on

magnetic pole strength.
separation distance.

Like kinds of magnetic poles repel while unlike kinds of magnetic poles

attract

Whereas electric charges can be isolated, magnetic poles

cannot

Refrigerator magnets are typically

short range

If you break a bar magnet in half you'll

have two magnets

Surrounding every magnet is

an electric field.
a magnetic field.

Magnetic fields are produced by

all moving electrical charges.

Surrounding every moving electron and stationary electron is

a magnetic field.
an electric field.

Magnetism is due to the motion of electrons as they

move around the nucleus.
spin on their axes.

The conventional direction of magnetic field lines outside a magnet are from

north to south.

Magnetic field strength about a magnet is strongest where magnetic field lines are

closer together

An iron rod becomes magnetic when

the net spins of many of its electrons are aligned.

The magnetic fields of a pair of nearby magnets can

add or subtract by vector rules.

The end of a compass needle that points to the south pole of a magnet is the

north pole.

A compass needle in a magnetic field

may experience a pair of torques.

Magnetic domains normally occur in

iron

In the atoms of most materials the fields of individual electrons

cancel one another.

Wood does not have magnetic properties because it contains no

magnetic domains.

To weaken a bar magnet

drop it on a hard surface.
put it in hot flames.
whack it with a hammer.

Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a

north pole.

Magnetic field lines about a current-carrying wire

circle the wire in closed loops.

When current reverses direction in a wire, the surrounding magnetic field

also reverses direction.

When a current-carrying wire is bent into a loop, its magnetic field inside the loop

becomes concentrated.

A beam of electrons passing through a magnetic field experiences maximum deflection if the direction of the beam is

perpendicular to the field lines.

A beam of electrons can pass through a magnetic field without being deflected if the direction of the beam is

parallel to the field lines.

A current-carrying loop of wire experiences no tendency to rotate in a magnetic field when

no field lines pass through the loop.

A current-carrying coil of wire is

an electromagnet.

Place an iron rod inside a current-carrying coil of wire and you

increase the strength of the electromagnet.

A superconducting magnet uses

superconducting coils.

Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet A exerts on magnet B is

exactly 100 N.

Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is

equally huge.

Into which stable force field can a proton be placed at rest without being acted upon by a force?

magnetic field

The direction of the force exerted on a moving charge in a magnetic field is

at right angles to the direction of the motion.

The force on an electron moving in a magnetic field will be least when its direction is

the same as the magnetic field direction.

When an electron passes through the magnetic field of a horseshoe magnet, the electron's

direction is changed.

The force exerted on an electron moving in a magnetic field is maximum when the electron moves

perpendicular to the magnetic field.

The force a magnetic field exerts on a current-carrying wire is maximum when the wire is oriented

perpendicular to the magnetic field.

A current-carrying wire in a magnetic field

may be deflected.
may experience a force.

An electron beam directed through a magnetic field

may experience a force.
may be deflected.

No net force acts on a loop of wire in a magnetic field when

no current is in the loop.
no magnetic field lines pass through the loop.

If a magnet produces a force on a current-carrying wire, the wire

produces a force on the magnet.

A galvanometer indicates

a flow of electrons.

A galvanometer can be calibrated to measure

electric current.
electric voltage.

Although a magnet can change the direction of travel of an electron beam, it cannot change its

speed
kinetic energy.

Which force field can increase a moving electron's speed?

electric field

Which force field can accelerate an electron?

electric field
magnetic field

Over geologic history the Earth's magnetic field

has reversed direction many times.

Solar winds headed in Earth's direction are deviated mainly by

Earth's magnetic field.

The intensity of cosmic rays bombarding the Earth's surface is most at the

poles

Cosmic rays penetrate your body when

outdoors.
in mountainous regions.

Earth's magnetic field is

protective to life on Earth.

Pigeons navigate primarily by