Magnetism and Electromagnetism

Question 1

What is a magnetic field?

Answer 1

The region around a magnet, where a force acts on another magnet or magnetic material.

Question 2

What are permanent magnets?

Answer 2

Magnets which produce their own magnetic field.

Question 3

What are induced magnets?

Answer 3

Magnets which become magnetised when placed in a magnetic field.

Question 4

In what direction do arrows on field liners always run?

Answer 4

From north to south.

Question 5

What is flux density?

Answer 5

The density of the field lines, which indicates the strength of the field at that point (the more concentrated the liners; the stronger the field).

Question 6

What can a compass show?

Answer 6

The fact that the needle aligns with the Earth’s magnetic field, proves that Earth’s core must be magnetic.

Question 7

What happens when a current flows in a conducting wire?

Answer 7

A magnetic field is produced around the wire.

Question 8

What does the right hand grip method show?

Answer 8

The direction of the field lines depending on the direction of current.

Question 9

How does the right hand grip method work?

Answer 9

The way the fingers point represent the direction of the magnetic field.
The direction the thumb is pointing represents the direction of current.

Question 10

What does the strength of a magnetic field depend on?

Answer 10

The size of the current and the distance from the wire.

Question 11

When is a solenoid formed?

Answer 11

When wire is looped into a cylindrical coil.

Question 12

How does a solenoid increase the strength of the magnetic field?

Answer 12

It creates a strong, uniform field inside the solenoid.
It concentrates a longer piece of wire into a smaller area.
The looped shape means that the magnetic field lines around the wire are all in the same direction.

Question 13

How can one increase the field strength?

Answer 13

By making a solenoid.

By giving it an iron core.

Question 14

Describe how an electric bell works.

Answer 14

The electromagnet is magnetised, which attracts armature.
The hammer strikes the gong and breaks the circuit.
The armature springs back, completing the circuit again and demagnetising the electromagnet.

Question 15

What is the motor effect?

Answer 15

When a current carrying conductor is placed in a magnetic field and it experiences a force.

Question 16

What causes the motor effect?

Answer 16

The field created by the current interacting with the magnetic field.

Question 17

How might the force if a magnetic field be increased?

Answer 17

By increasing the size of the current, the length of conductor, the flux density.

Question 18

What happens if the direction of the current or the direction of the magnetic field is reversed?

Answer 18

The direction of the force will reverse.

Question 19

What does Fleming’s left hand rule find?

Answer 19

The direction of the force on the conductor.

Question 20

What position is Fleming’s left hand rule?

Answer 20

When the thumb, first and second finger on the left hand are all at right-angles.

Question 21

In Fleming’s left hand rule, what does the first finger represent?

Answer 21

The direction of the magnetic field, from north to south.

Question 22

With a rotation of the wrist to re-align the second finger, where should it now point?

Answer 22

Along the wire in the direction the current is flowing.

Question 23

In Fleming’s left hand rule, where should the thumb finally be pointing?

Answer 23

The direction of force.

Question 24

Why will a current carrying coil in a magnetic field rotate?

Answer 24

The current going up one side of the coil is in the opposite direction to the current coming back down the other side, so one side moves up and the other side moves down.

Question 25

In electric motors, what does the brush contacts at the commutator do?

Answer 25

It ensures that the current direction in the coil is always the same direction.
This makes sure that the motor keeps rotating and does not stop.

Question 26

What will make an electric motor run faster?

Answer 26

Increasing the current or magnetic field.

Question 27

How could one make an electric motor rotate in another direction?

Answer 27

By reversing the current of the magnetic field.

Question 28

In motors, what is the motor effect used to do?

Answer 28

Convert electrical emery into kinetic energy.