Topic 13 - Electromagnetic Induction

Question 1

What happens when an electrical conductor moves relative to a magnetic field?

Answer 1

A voltage is induced across the conductor

Question 2

What happens to an electrical conductor when there is a change to the magnetic field that it is placed in?

Answer 2

The voltage is also changed

Question 3

How do you produce an electric current using a magnet and a conductor on a small-scale?

Answer 3

Moving a coil of wire between magnetic poles
Moving a magnet within a coil of wire
Once a voltage is induced, if there is a complete circuit, a current will also be induced

Question 4

How is electrical current produced Ona large-scale?

Answer 4

An electromagnet is rotated around a coil

Question 5

What factors affect the size of an induced voltage?

Answer 5

The number of turns on the coil of wire
How strong the magnetic field is
The speed of the movement

Question 6

What is the requirement for an induced potential difference to cause a current flow?

Answer 6

The conductor must form a closed loop or be part of a complete circuit

Question 7

What can be said about the direction of the magnetic field produced by an induced current?

Answer 7

The direction of the field is such that it opposes the charge that induced the current. This change is either the movement of the conductor or a change to the field

Question 8

What are two ways treat the generator effect is used to generate different types of current?

Answer 8

In a Dynamo to produce direct current

In an alternator to produce alternating current

Question 9

How does a Dynamo generate current?

Answer 9

A coil of wire rotates inside a magnetic field. A commutator is used to ensure it continues rotating in the same direction, therefore keeping the current flowing in the same direction

Question 10

How is electromagnetic induction used in alternators to generate alternating current?

Answer 10

A coil of wire rotates in a magnetic field. The end of this coil is connected to slip rings which will cause the current to change direction while rotating. This means a.c is produced

Question 11

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

Answer 11

The generator effect

It converts the pressure variations in sound waves into alternating current

Question 12

How do loudspeakers make use of the motor effect?

Answer 12

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

Question 13

Explain how a loudspeaker works

Answer 13

A cone wrapped in wire is connected to an A.C power supply and is placed in a permanent magnetic field
When current flows through the wire, it creates a magnetic field which interacts with the permanent field
This produces a force which causes the cone to vibrate, producing sound

Question 14

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

Answer 14

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

Question 15

How do microwaves convert sound into electrical signals?

Answer 15

Sound produces pressure variations which cause the diaphragm to vibrate
A coil of wire is connected to the diaphragm, so as the diaphragm moves, the coil also moves
Movement in a magnetic field = a voltage is induced
As there is a complete circuit a current is also created

Question 16

Describe the makeup of a basic transformer

Answer 16

A primary coil and a secondary coil of wire wrapped around an iron core

Question 17

Why is iron used as the core for a transformer?

Answer 17

It is easily magnetised

Question 18

Explain how a transformer works

Answer 18

An alternating current flows through the primary coil, this induces a changing magnetic field in the core. This changing magnetic field induces a current in the secondary secondary coil, changing the voltage

Question 19

Why must the current flowing through the primary coil of a transformer be alternating?

Answer 19

For current to be induced int eh secondary coil, the magnetic field in the core must be continuously changing. For the magnetic field to be changing, the current in the primary coil must be alternating

Question 20

What is the relationship between the output and input of an 100% efficient transformer?

Answer 20

They are equal

Question 21

Give an equation linking number of turns with potential difference in transformers

Answer 21

Primary potential difference/ secondary difference = primary turns/ secondary turns

Question 22

State the power equation for transformers with a 100% efficiency

Answer 22

Primary voltage x primary current = secondary voltage x secondary current

Question 23

On a step-down transformer, does the secondary coil have more or fewer turns?

Answer 23

The secondary coil has fewer turns

Question 24

What is an advantage of a step down transformer in the national grid?

Answer 24

It means that the voltage can be reduced to a value safe enough to be used in houses

Question 25

Why is it important to have step up transformers in the national grid?

Answer 25

It can increase efficiency

Question 26

How does a step up transformer work?

Answer 26

The primary coil has fewer turns. An A.c current produced a magnetic field in the primary coil. The iron core passes the magnetic field to the secondary coil. The magnetic field induces a higher voltage in the secondary coil. Power is conserved, so this produces a lower current

Question 27

Where are step-up and step-down transformers used in the national grid?

Answer 27

Step-up transformers are used at power stations, whilst step-down transformers are used domestically