Chapter 20

What do scientists currently believe causes Earth’s magnetic field?

Earth’s magnetic field is thought to be caused by the movement of molten iron in the planet’s outer core.

Permanent magnets are made of what kind of material?

ferromagnetic

What is the distinction between a magnet and magnetic field?

A magnet is a material or object that can produce a magnetic field. The field itself is the region that experiences a magnet’s magnetic influence.

Is Earth’s magnetic North Pole an actual magnetic north pole? Explain.

No. Earth’s magnetic field lines point from geographic south to north, so Earth’s magnetic “north” pole actually functions as a magnetic south pole.

How does Earth’s magnetic field make life on the planet possible?

Earth’s magnetic field shields our planet from the harmful particles of the solar wind.

Topographic maps usually include an indication of the angular difference, called the magnetic declination, between true north and magnetic north on the map. Why is the declination shown on a forty-year-old map likely to be incorrect?

Earth’s magnetic poles are constantly moving, so the declination for a particular map changes over time.

Describe how a temporary magnet can be made.

by repeatedly running a permanent magnet along the length of a metal object such as a nail or sewing needle.

What is electromagnetic induction?

Electromagnetic induction is the production of an electric current by changing a magnetic field.

Apart from converting it into an electromagnet, how can the strength of a solenoid’s magnetic field be increased?

by adding more electric current or by adding additional wire loops

How do magnets cause electromagnetic induction?

The magnetic field of a moving magnet exerts a force on the charge carriers within a wire, causing them to move.

How is electromagnetism used in a particle accelerator?

Electromagnetism accelerates charged particles, focuses beams of charged particles, and bends their paths to keep them from colliding with the walls of the accelerator.

Why does part of a generator have to rotate?

The rotation changes the relative positions of the magnetic field and the wire coil. It is this change that generates the current.

What function does a commutator serve?

A commutator ensures that the electrical current produced by a DC generator flows in only one direction.

Briefly describe three uses for electromagnets.

• lifting heavy metal objects

• sorting magnetic from nonmagnetic metals

• focusing beams of charged particles in accelerators

• for the creation of superconducting magnets, in the pickups for musical instruments

• maglev trains.