CP11

Question 1

What is a transformer?

Answer 1

A device that can change the voltage of an electricity supply.

Question 2

What is a transformer made using?

Answer 2

A transformer is usually made using two coils of wire wound onto an iron core. There is no electrical connection between the two coils of wire.

Question 3

What does electromagnetic induction mean?

Answer 3

Electromagnetic induction means that the voltage in one coil causes (induces) a voltage in the second coil. This happens in a transformer.

Question 4

How do you calculate electrical power (symbol equation)?

Answer 4

P=I x V
I = current
V = potential difference
P = Electrical power

Question 5

What is the equation for electrical power?

Answer 5

Electrical power(W) = Current(A) x Potential difference(V)

Question 6

How is the power supplied to the transformer in the primary coil proportional to the power transferred away from the transformer in the secondary coil?

Answer 6

The power supplied to a transformer in the primary coil must be equal to the power transferred away from the transformer in the secondary coil.

Question 7

What is the equation involving primary and secondary coils?

Answer 7

Potential difference across the primary coil(V) x Current in primary coil(A) = Potential difference across secondary coil(V) x Current in secondary coil(A)

Question 8

What is the symbol equation for primary and secondary coils?

Answer 8

Vₚ x Iₚ = Vₛ x Iₛ
(Vₚ=Potential difference across primary coil, Iₚ=Current in primary coil, Vₛ=Potential difference across secondary coil, Iₛ=Current in secondary coil)

Question 9

What is the national grid?

Answer 9

The system of wires and transformers that distributes electricity around the country.

Question 10

How is energy wasted in transmission lines of the national grid?

Answer 10

When electricity flows through a wire, the wire gets warm. There is a significant amount of energy wasted by heating in the transmission lines of the national grid.

Question 11

What is a step-up transformer?

Answer 11

A step-up transformer is a transformer that increases the voltage and decreases the current at the same time.

Question 12

What is a step-down transformer?

Answer 12

A step-down transformer is a transformer that makes the voltage lower and the current higher.

Question 13

Why are transformers able to work?

Answer 13

Because a changing magnetic field induces a potential difference in a wire, which causes a current to flow.

Question 14

How is a potential difference induced in a wire?

Answer 14

1. By using a changing magnetic field
2. If a wire is moved in a magnetic field

Question 15

What does the size of induced potential difference depend on?

Answer 15

• The number of turns in a coil of wire
• How fast the magnetic field changes or moves past the coil

Question 16

What does reversing the direction of the magnetic field do?

Answer 16

Reversing the direction of the magnetic field reverses the direction of the induced current.

Question 17

If the potential difference causes a current to flow to a wire, what does magnetic field in the current do?

Answer 17

If the potential difference causes a current to flow in a wire, the magnetic field of this current opposes the original change.

Question 18

How do transformers work?

Answer 18

Transformers work with alternating currents, when the direction of the potential difference (and so also the current) changes many times each second. The alternating current in the primary coil creates a continuously changing magnetic field, and the iron core of the transformer carries this magnetic field to the secondary coil. The changing magnetic field induces a changing potential difference in the secondary coil. The potential difference is greater in the secondary coil if it has more turns than the primary coil.

Question 19

Why are high voltages used in transformers?

Answer 19

They use high voltages with low currents to flow through transmission lines. A smaller current flowing through the transmission lines results in less heat being produced in the wire. This will reduce the energy loss in the transmission lines as less heat is less energy wasted. After transferring it over a long distance, the voltage is then reduced again before the electricity is sent to factories and other buildings.

Question 20

What are transmission lines?

Answer 20

The wires (overhead or underground) that take electricity from power stations to towns and cities.

Question 21

What is the average voltage for homes and shops after being reduced by a transformer?

Answer 21

Transformers in local sub-stations reduce the voltage to 230V for homes, shops and offices.

Question 22

What is the average voltage for factories after being reduced by a transformer?

Answer 22

Transformers reduce the voltage to 33,000V or 11,000V for factories.

Question 23

Describe the process of the national grid from the power station to a home/factory?

Answer 23

Energy is produced at a power station, this is roughly 25kV. Transformers increases the voltage to 400,000V(400kV) to reduce the amount of energy wasted by heating in the transmission lines. Transformers reduce the voltage to 11,000V for factories, or reduce the voltage to 230V for homes, shops and offices.