Magnetism and Electromagnetism

Question 1

What do all magnets have?

Answer 1

Two poles

North and South

Question 2

What do magnetic field lines show?

Answer 2

the size and direction of magnetic fields

Question 3

What is a magnetic field?

Answer 3

A region where magnetic materials experience a force

Question 4

What direction do magnetic field lines point?

Answer 4

North to South

Question 5

What kind of field will you find when you place the North and South poles of two permanent bar magnets near each other?

Answer 5

A uniform field

Question 6

What two things can you use to investigate magnetic field patterns?

Answer 6

Compasses and Iron Fillings

Question 7

A current-carrying wire creates a ….

Answer 7

magnetic field

Question 8

The larger the electric current….

Answer 8

the stronger the magnetic field

Question 9

What causes a wire to move?

Answer 9

When a current carrying wire is put between magnetic poles, the two magnetic fields affect one another. The result is a force on the wire.

Question 10

Where does a wire have to be in proportion to the magnetic field?

Answer 10

at 90 degrees

Question 11

What’s a good way of showing the direction of the force?

Answer 11

To apply current to a set of rails inside a horseshoe magnet.
A bar is placed on the rails which completes the circuit.
This generates a force that rolls the bar along the rails.

Question 12

The stronger the magnetic field…

Answer 12

The stronger the force

Question 13

What happens when you reverse the current or magnetic field?

Answer 13

The direction of the force also reverses

Question 14

What can you do to remember the way which force acts?

Answer 14

Fleming’s Left-Hand Rule

Question 15

Name 4 factors that will speed up an A.C electric motor

Answer 15

More current
More turns on the coil
Stronger magnetic field
A soft iron core in the coil

Question 16

How can the direction of an A.C motor be reversed?

Answer 16

Swapping the polarity of the d.c supply

Swapping the magnetic poles over

Question 17

How do loudspeakers work?

Answer 17

A.C electrical signals from an amplifier are fed to a coil of wire in the speaker which os wrapped around the base of a cone
The coil is surrounded by a permanent magnet so the a.c signals cause a force on the coil and make it move back and fourth
The movements make the cone vibrate and this creates sounds

Question 18

What is electromagnetic induction?

Answer 18

The creation of voltage (and maybe current) in a wire experiencing a change in magnetic field

Question 19

What is the dynamo effect?

Answer 19

Using electromagnetic induction to transform kinetic energy into electrical energy

Question 20

Name the two ways you can get EM induction

Answer 20

When an electrical conductor moves through a magnetic field

When the magnetic field through an electrical conductor changes

Question 21

How can you test the dynamo effect?

Answer 21

By connecting an ammeter to a conductor and moving the conductor through a magnetic field
The ammeter will show the magnitude and direction of the induced current

Question 22

To get a bigger voltage in the dynamo effect you can…

Answer 22

INCREASE
strength of magnet
number of turns on the coil
speed of movement

Question 23

Like poles…

Answer 23

repel

Question 24

Opposite poles…

Answer 24

attract

Question 25

How does magnetic induction occur?

Answer 25

When a magnet is brought near a magnetic material, that material acts as a magnet.

Question 26

The closer the magnet and the magnetic material get...

Answer 26

The stronger the induced magnetism

Question 27

What is the magnetic field inside a current carrying solenoid like?

Answer 27

strong and uniform

Question 28

What is the magnetic field outside a current carrying solenoid like?

Answer 28

Like the one around a bar magnet.

Question 29

What is a solenoid magnet a type of?

Answer 29

electromagnet

Question 30

When is a magnetic material considered 'soft' ?

Answer 30

If it loses it's induced magnetism quickly

Question 31

When is a magnetic material considered 'hard' ?

Answer 31

If it keeps it's induced magnetism permanently

Question 32

Name an example of a soft magnetic material and a hard material.

Answer 32

Soft - Iron | Hard - Steel

Question 33

How can increase the strength of the magnetic field around a solenoid?

Answer 33

By adding a 'soft' iron core through the middle

Question 34

What do transformers do?

Answer 34

Change the size of the voltage of an alternating current

Question 35

What do transformers have?

Answer 35

Two coils, the primary and secondary, joined with an iron core.

Question 36

What happens when an alternating voltage is applied across the primary coil of a transformer?

Answer 36

The magnetically soft iron core magnetises and demagnetises quickly, inducing an alternating voltage in the secondary coil.

Question 37

In a transformer, the ratio between the primary and secondary voltages is the same as...

Answer 37

The ratio between the number of turns on the primary and secondary coils

Question 38

What do step-up transformers do?

Answer 38

Step the voltage up. They have more coils on the secondary coil than on the primary coil/

Question 39

What do step-down transformers do?

Answer 39

Step the voltage down. They have more turns on the primary coil than in the secondary.

Question 40

What is the transformer equation?

Answer 40

Input (primary) Voltage / Output (secondary) Voltage = No. of turns on primary / No. of turns on secondary

Question 41

Another way of saying input power = output power

Answer 41

VpIp = VsIs

Question 42

How do transformers work when transmitting electricity across the country?

Answer 42

- The voltage produced by power stations is too low to be transmitted efficiently, so a step-up transformer is used to boost the voltage before it is transmitted - Step-down transformers are used at the end of the journey to reduce the voltage so it's more useful and safer to use