Magnetism and Electromagnetism

Question 1

The strongest parts of metals are its ________

Answer 1

Poles

Question 2

Permanent magnets are made up of ___________. Example:

Answer 2

Magnetically hard material eg. steel

Question 3

Iron is a magnetically __________ and can therefore be only used as a ______________

Answer 3

soft material

temporary magnet

Question 4

What is a magnetic field?

Answer 4

A volume of space around a magnet where magnetism can be detected

Question 5

Two ways to show the patterns of the magnetic field around a magnet:

Answer 5

Iron filings

Small compasses

Question 6

Main features of the magnetic field lines:

Answer 6

• Show the shape of the magnetic field
• Show the direction of the magnetic force
• Show the strength of the magnetic field

Question 7

What is the neutral point in a magnetic field?

Answer 7

It is the point where forces of both magnets cancel out and so there is no resultant magnetic field/force there

Question 8

How can we make a uniform magnetic field?

Answer 8

By taking the opposite poles of two magnets and holding them close together

Question 9

What are the features of a uniform magnetic field?

Answer 9

• Its strength and direction are the same at all points

Question 10

What is induced magnetism?

Answer 10

Induced magnetism is when a permanent magnet is brought near to a magnetic material that becomes temporarily magnetized

Question 11

What is electromagnetism?

Answer 11

Electromagnetism is a phenomenon that occurs when a magnetic field is created around a wire that has a current flowing through it

Question 12

The features of a magnetic field created around a current-carrying wire:

Answer 12

• Has a definite direction from N to S
• Quite weak
• Circular in shape
• Can change directions if the direction of the current flowing through it changes

Question 13

The strength of a magnetic field around a current-carrying conductor can be increased by:

Answer 13

• Increasing the current in the wire

- Wrapping the wire into a coil or a solenoid

Question 14

The strength of a magnetic field around a solenoid can be increased by:

Answer 14

• Increasing the current in the solenoid
• Increasing the no. of turns on a solenoid
• Wrapping the solenoid around a magnetically soft core such as an iron

Question 15

Advantages of an electromagnet over ordinary magnets:

Answer 15

• It can be turned on and off

- Its magnetic field can be changed

Question 16

Uses of electromagnets:

Answer 16

Electric bell

Circuit breaker

Question 17

How is movement generated from electricity?

Answer 17

When a charged particle passes through a magnetic field, it experiences a force as long as its motion is not parallel to the field

Question 18

Explain the motor effect

Answer 18

When the two magnetic fields overlap, in some places where the direction of the magnetic field is the same, they reinforce each other, and where the magnetic fields are in opposite directions, a weaker force is produced. Due to the different strengths of the magnetic field, the wire feels a force acting on it from the stronger part to the weaker one

Question 19

Explain the functioning of a moving coil loudspeaker

Answer 19

• Electric currents from a source are supplied to the speaker’s coil
• These currents are always changing in direction and strength
• The overlapping magnetic field are also always changing direction and strength
• These fields, in turn, apply rapidly changing forces to the wires of the coil which cause the cone to vibrate
• These vibrations create the sound waves we hear

Question 20

The function of a split-ring commutator:

Answer 20

It connects the loop of wire to the electrical supply. The gap in the split-ring commutator changes the connections, the direction of the current flowing in the loop reverses which then reverses the direction of force acting on each side of the loop. The loop rotates continuously

Question 21

How can the size of induced voltage be increased?

Answer 21

• Move the wire more quickly
• Use a stronger magnet so more field lines are cut
• Wrapping the wire into a coil so that more pieces of wire cut through the magnetic field lines

Question 22

How does a dynamo work in bicycles?

Answer 22

The motion of the wheel causes a rotating magnet to turn. As it turns, so does the magnetic field. It cuts through the coil and induces a current in it that can then be used to light up the bicycle lights

Question 23

How do transformers work?

Answer 23

The alternating current in the primary coil creates a growing and collapsing field around the primary coil which cuts through the secondary coil. This induces an alternating output voltage in the secondary coil

Question 24

What is the function of transformers?

Answer 24

Transformers change the size of the alternating voltage by using different no. of turns in the primary and secondary coils

Question 25

How are transformers made energy efficient?

Answer 25

• Using thick copper wires

- A soft iron core covered in a thin layer of plastic to connect the two coils

Question 26

How are transformers used in national grids?

Answer 26

Step-up transformers: Increase voltage, decrease current

Step-down transformer: decreases the voltage, increases the current

Question 27

What is an alternator?

Answer 27

A generator that produces an a.c