Physics Ch 4: Electromagnetism

natural magnet

created when iron oxide remains in the earth's magnetic field for ages slowly orienting the magnetic dipoles in the same direction

Lodestones

Natural magnets are also called

Natural, artificial permanent, and electromagnets

Magnets can be classified by type of production. They are:

Artificial permanent magnet

Manufactured from a steel alloy called alnico, comprising aluminum, nickel, and cobalt.

The field of a strong commercial magnet to permit easier orientation of the magnetic dipoles.

While it is hot, alnico is subjected to:

relatively permanent

Upon cooling, the magnetic field of artificial permanent magnet becomes

Electromagnet

A temporary magnet produced by moving electric current

Repulsion-Attraction

Like poles repel; unlike poles attract.

Inverse square law

The force between two magnetic fields is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.

Magnetic poles

Every magnet has two poles, a north and south. No matter how much a magnet is divided, even into individual moving electrons, both poles continue to exist.

Permeability

the ease with which a material can be magnetized

Retentivity

The ability of a material to stay magnetized

Ferromagnetic

(Simply magnetic)

Materials, such as iron, cobalt, and nickel, are highly permeable and greatly susceptible to induction.

Lying in the same direction

Ferromagnetic materials have majority of their dipoles

Paramagnetic

Materials such as platinum and aluminum, have low permeability and weak attraction to magnetic fields.

In the same direction and there is little tendency for the size of the dipoles to grow

Paramagnetic materials have only slight majority of dipoles

Diamagnetic

Materials such as beryllium, bismuth, and lead; they are weakly repelled by all magnetic fields.

Water

Slightly diamagnetic

Nonmagnetic

Materials such as wood, glass, rubber and plastic; cannot be magnetized

1. Move the conductor

2. Move magnetic lines of force

3. Vary the magnetic flux

Three ways to create the motion between lines of force and a conductor

Move the conductor

Through a stationary, unchanging strength magnetic field

Move magnetic lines of force

Through a stationary conductor with an unchanging strength

Faraday's Law of Induction

States that four factors regulate the strength of induced current when magnetic lines of force and a conductor are in motion relative to one another

Four factors of Faraday's Laws

1. The strength of the magnetic field

2. The speed of the motion between lines of force and the conductor

3. The angle between the magnetic lines of force and reg conductor

4. The number of turns in the conducting coil

The direction in which the induced current will flow

Farady's Law makes it possible to determine

Generator

Mechanical energy into electric energy is a

transformer

Compromises two coils placed near one another (without electrical connection)

b. electric charges in motion.

A magnetic field is produced by:

a. electric charges at rest.

b. electric charges in motion.

c. permanent magnets only.

d. none of the above.

d. alternating current.

A continuous, expanding and contracting magnetic field is produced by:

a. a stationary magnet.

b. a steady current flowing in a wire.

c. a battery.

d. alternating current.

b. counterclockwise.

Electrons move downward in a vertical wire. The direction of the associated magnetic field directly around the wire is:

a. clockwise.

b. counterclockwise.

c. in the direction of the electron flow.

d. opposite to the conventional current.

d. both a and b.

The magnitude of force felt by a moving charge through a magnetic field would be least if the charge were:

a. moving directly into the magnetic field.

b. moving directly away from the magnetic field.

c. moving at a right angle to the magnetic field.

d. both a and b.

b. electrical energy into mechanical energy.

A motor is a device that converts:

a. thermal energy into electrical energy.

b. electrical energy into mechanical energy.

c. electrical energy into electromagnetic energy.

d. mechanical energy into electrical energy.

a. has a greater secondary voltage.

A transformer with more secondary windings than primary windings:

a. has a greater secondary voltage.

b. is a step-down transformer.

c. has a greater power output than input.

d. has a higher power loss.

d. the transformer turns ratio.

The efficiency of a transformer is not affected by:

a. eddy current loss.

b. power loss.

c. hysteresis loss.

d. the transformer turns ratio.

c. They work most efficiently on pulsating DC.

All of the following are true of transformers EXCEPT:

a. They have no moving parts.

b. They work on the principle of mutual induction.

c. They work most efficiently on pulsating DC.

d. They are designed to regulate voltage.

c. number of windings.

The turns ratio of a transformer is determined by the:

a. size of the wire.

b. type of wire.

c. number of windings.

d. size of the laminated plates.

step-up transformer

a transformer that increases voltage

step-down transformer

a transformer that decreases voltage