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A magnet can be used to induce a potential difference at the ends of a coil of wire.

Electricity - Transformers

Transformers change the voltage in a circuit so electricity can be transmitted efficiently and used safely. This quiz checks your understanding of step-up and step-down transformers.

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Fascinating Fact:

Transformers work using electromagnetic induction, with two coils of wire wrapped around a soft iron core.

In GCSE Physics, you learn how transformers use alternating current and electromagnetic induction to change voltage. This allows electricity to be transmitted at high voltages and then reduced to safer values for everyday use.

Key Terms

Transformer: A device that changes the potential difference of an alternating current supply, usually stepping voltage up or down.
Primary coil: The coil in a transformer that is connected to the input alternating voltage from the supply.
Secondary coil: The coil in a transformer that is connected to the output circuit and provides the transformed voltage.

Frequently Asked Questions (Click to see answers)

What does a transformer do in an electrical circuit?

A transformer changes the potential difference of an alternating current supply. It can increase the voltage, decrease it, or keep it similar, depending on the number of turns on each coil.

What is the difference between a step-up and a step-down transformer?

A step-up transformer has more turns on the secondary coil, so it increases voltage and reduces current. A step-down transformer has fewer turns on the secondary, so it reduces voltage and increases current.

Why are transformers important in the National Grid?

Transformers step up voltage for transmission so current is low and energy loss in cables is reduced. Near homes and businesses, step-down transformers reduce the voltage to safer levels for everyday use.

Try These Related Quizzes

1 .

What is induced across the ends of an electrical conductor which moves through a magnetic field?

A potential difference

A resistance

A current

A capacitance

Potential difference is often referred to as voltage

2 .

What can be used to induce a potential difference at the ends of a coil of wire?

Heat

A vacuum

Magnet

Bread

Moving a magnet inside the coil produces a changing magnetic field, causing a potential difference to build. A potential difference is only induced for as long as the magnet is moving

3 .

Considering the basic structure of a transformer, what does an alternating current in a primary coil produce in the iron core which it surrounds?

A static magnetic field

A changing magnetic field

A static electric field

A changing electric field

The iron core concentrates the magnetic field and ensures that it passes directly through the secondary coil

4 .

In a step-up transformer, is the potential difference created in the secondary coil more, less or equal to the potential difference in the primary coil?

Less

Equal

Values for the coils are required to calculate this

Knowing that the transformer is a step-up transformer is enough to know that the potential difference will be greater in the secondary coil than the first

5 .

In a step-down transformer, is the potential difference created in the secondary coil more, less or equal to the potential difference in the primary coil?

Less

Equal

Values for the coils are required to calculate this

Step-down (and step-up) refers to voltage, remembering that small fact will help you in transformer and perhaps National Grid exam questions

6 .

Which equation correctly relates the potential difference across the primary and secondary coils of a transformer?

^V_p⁄_{V_s} = ^n_p⁄_{n_s}

^V_p⁄_{V_s} = ^n_s⁄_{n_p}

^V_s⁄_{V_p} = ^n_p⁄_{n_s}

^V_p⁄_{V_p} = ^n_p⁄_{n_s}

If a transformer was assumed to be 100% efficient, the electrical power output would equal the electrical power input. Thus the following formula would also be true: V_p x I_p = V_s x I_s

7 .

Which types of transformers operate at high frequency?

Laminated core

Variac

Stray field

Switch mode transformers

These are useful in phone, tablet and laptop chargers

8 .

What is an advantage of using switch mode transformers over a traditional transformer when working from a 50 Hz mains supply?

They change the electricity at a quicker rate

They are lighter and smaller

They are more robust

They are more efficient

They are therefore more portable and can easily slip into your luggage when going on a school trip or holiday

9 .

What is another advantage of using switch mode transformers when no load is applied?

They use little power

They use lots of power

They store electricity

There is no advantage offered by switch mode transformers when no load is applied

One of the issues with normal transformers is that when an appliance is switched on but in standby mode, the transformer is still operating at almost full power, which is a waste of energy

10 .

A primary coil within a transformer has 48 turns around its coil and has a potential difference applied to it of 12 V. If the secondary coil has 60 turns around its coil, what is the potential difference produced at the ends of the secondary coil?

12 V

14 V

15 V

9.6 V

Either use the transformer equation or simple proportion to arrive at the correct answer. Because the secondary coil is larger than the primary, you should already know the potential difference should be greater which immediately eliminates two of the answers

You can find more about this topic by visiting BBC Bitesize - Transformers

Author: Martin Moore