a coil of insulated wire in a transformer, across which potential difference is applied

a coil of insulated wire in a transformer, across which potential difference is induced

pure iron inside the coil of an electromagnet that loses all of its magnetism when the electromagnet turns off

the p.d. across a conductor caused by a magnetic field moving relative to it

the proportion or percentage of energy supplied to a device that is transferred in a useful way

Transformers

Physics

Danger from electric shock

Short circuits and earth wires

Power of an appliance or electric circuit

Calculating with electric charge: including complex calculations

The National Grid

Energy resources

In the Circuit components unit, pupils learnt how the resistance of filament lamps and diodes change with current and about the properties and applications of light dependent resistors and thermistors.

This unit covers UK domestic a.c. supply, mains wiring safety, energy changes in electrical systems, power ratings, and energy transfer. It explains the National Grid, transformers, energy sources, and calculations for energy changes and power transmission efficiency.

Mains electricity

when there is a changing magnetic field in the primary coil

when the primary coil is connected to a direct current

when the secondary coil is connected to a battery

When is a p.d. (potential difference) induced across the secondary coil of a transformer?

Which of the following can a transformer increase?

Fewer turns always mean higher potential difference.

More turns always mean higher potential difference.

The number of turns does not affect the potential difference.

The ratio of turns equals the ratio of potential difference.

How does the number of turns on the coils affect the potential difference in a transformer?

Calculate the output p.d. of a transformer if the primary p.d. is 240 V, the primary coil has 50 turns, and the secondary coil has 25 turns.

If the power input to a transformer is 1000 W and the power output is 950 W, what is the efficiency of the transformer?

What current is drawn from a 230 V power supply to a transformer if the output is 15.0 V and 1000 mA? Give your answer in mA to 3 s.f.

describes the coil across which p.d. is applied

describes a transformer that increases the p.d.

describes a transformer that decreases the p.d.

describes the coil across which p.d. is induced

Match the following terms, which are related to transformers, to the correct definitions.

percentage of energy supplied that is wasted

difference between energy supplied and wasted energy

amount of energy supplied that is transferred in a useful way

percentage of total energy transferred that is transferred usefully

difference between energy supplied and energy usefully transferred

Which of the following is a definition of the efficiency of a device?

Which of the following is the frequency of mains electricity?

Match each of the following to the typical voltage(s) it supplies or requires.

placing the coil in a changing magnetic field

moving the coil in an unchanging magnetic field

moving the coil and a bar magnet together at the same velocity

Which of the following induce a potential difference across the ends of a coil of wire?

A transformer with 100% efficiency changes the voltage from 1000 V to 33 kV. If the current through the secondary coil is 20 A, the current through the primary coil is {{}} A.

Transformers

Lesson outcome