Topic 7 - Magnetism and Electromagnetism

Question 1

What is an alternator?

Answer 1

A device that makes use of the generator effect to generate alternating current.

Question 2

What is attraction?

Answer 2

Opposite poles will experience a force of attraction, meaning they will
experience a force towards each other. The force between a magnet and
magnetic material is always one of attraction.

Question 3

What are current carrying wires?

Answer 3

When current flows through a wire, a magnetic field is
generated around it. The strength of the field is dependent on the magnitude of the current and the distance from the wire.

Question 4

What is a dynamo?

Answer 4

A device that makes use of the generator effect to generate direct current.

Question 5

What is an electric motor?

Answer 5

A current-carrying coil of wire in a magnetic field. The two sides of the coil that are perpendicular to the magnetic field experience
forces in opposite directions, causing rotation.

Question 6

What is a electromagnet?

Answer 6

A solenoid with an iron core.

Question 7

What is Fleming’s left hand rule?

Answer 7

A rule used to determine the orientation of the force (thumb), current (second finger) and magnetic field (first finger) when a
current-carrying wire is placed in a magnetic field (motor effect).

Question 8

What is the generator effect?

Answer 8

When there is relative motion between an electrical
conductor and a magnetic field, a potential difference will be induced across
the ends of the conductor. A current will flow if this conductor is part of a
complete circuit.

Question 9

What is an induced magnet?

Answer 9

A material that becomes a magnet when it is placed in an existing magnetic field, but loses its magnetism quickly once it is removed.
Induced magnetism always produces attractive forces.

Question 10

What is a magnetic compass?

Answer 10

A device containing a small bar magnet that points in the direction of the Earth’s magnetic field.

Question 11

What are magnetic field lines?

Answer 11

Lines representing the strength and direction of a magnetic field. The field line direction at any point is in the direction that a force would act on another north pole if placed at that point.

Question 12

What are magnetic fields?

Answer 12

The region around a magnet in which another magnet or
magnetic material will experience a force.

Question 13

What are magnetic materials?

Answer 13

Iron, steel, cobalt and nickel.

Question 14

What are magnetic poles?

Answer 14

The regions of a magnet where the magnetic forces are at their strongest.

Question 15

What is a microphone?

Answer 15

A device that uses the generator effect to convert the pressure variations of sound waves into variations in the electrical current of a circuit.

Question 16

What is the motor effect?

Answer 16

When a current-carrying wire is placed in a magnetic field, a force will be experienced between the wire and the magnet responsible for the field.

Question 17

What is a permanent magnet?

Answer 17

A magnet that produces it’s own magnetic field.

Question 18

What is repulsion?

Answer 18

Like-poles will experience a force of repulsion, meaning they will experience forces in opposite directions.

Question 19

What is a solenoid?

Answer 19

A wire wrapped into the shape of a coil, that has a strong and uniform magnetic field inside of it. The solenoid’s magnetic field strength can be increased
by adding an iron core.

Question 20

What is a step down transformer?

Answer 20

A transformer that has a smaller potential difference in the secondary coil than in the primary core.

Question 21

What is a step up transformer?

Answer 21

A transformer that has a larger potential difference in
the secondary coil than in the primary core.

Question 22

What are Tesla?

Answer 22

The unit of magnetic flux density.

Question 23

What is a transformer?

Answer 23

An iron core with a primary and secondary coil of wire wound around opposite ends.

Question 24

What is the difference between a permanent magnet and an induced magnet?

Answer 24

• A permanent magnet produces it’s own magnetic field
• An induced magnet becomes magnetic when placed in a magnetic field

Question 25

In what direction does a magnetic field point?

Answer 25

- In the direction that a north pole would experience a force if played in the field - From the north seeking pole to the south seeking pole of a magnet

Question 26

What is produced when current flows through a conducting wire?

Answer 26

A magnetic field is produced around the wire.

Question 27

Describe the magnetic field found inside a solenoid?

Answer 27

Strong and Uniform.

Question 28

What criteria must be met for the equation linking force, magnetic flux density, current and length to hold?

Answer 28

The conductor must be at right- angles to the magnetic field it is placed in

Question 29

How do loudspeakers make use of the motor effect?

Answer 29

The motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound.

Question 30

Explain how a loudspeaker works.

Answer 30

- A cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field - When current flows through the wire, it created a second magnetic field, which interacts with the permanent field. - This produces a force which causes the cone to vibrate

Question 31

How is the pitch of the sound from a loudspeaker changed?

Answer 31

- The frequency of the a.c current is altered - This creates a different frequency of vibration in the cone

Question 32

What electromagnetic effect does a microphone take advantage of and how?

Answer 32

- The generator effect - It converts the pressure variations in sound waves into alternating current in a circuit.