A fuse is a safety device that cuts off the flow of electricity to an appliance if the current becomes too large. It contains a thin wire that heats up and melts, breaking the circuit.

Define double insulation .

Double insulation means an appliance has two layers of insulation — insulation around the wires and a non-metallic case — so it cannot become electrified and does not need an earth wire.

Name three common electrical hazards found in the home.

Any three from: damaged insulation , overheating of cables , damp conditions , and excess current from overloaded plugs, extension leads or sockets .

State the frequency and potential difference of the UK mains electricity supply.

The UK mains supply has a frequency of 50 Hz and a potential difference of about 230 V .

Describe what happens if a live wire touches the metal case of an earthed appliance.

The earth wire provides a low resistance path to earth. This causes a surge of current in the earth wire and the live wire. The high current melts the fuse , breaking the circuit and cutting off the electricity supply, making the appliance safe.

Mains electricity in the UK is an ______ current supply, meaning the direction of current changes back and forth 50 times a second.

Mains electricity in the UK is an alternating current supply, meaning the direction of current changes back and forth 50 times a second.

True or False? A trip switch performs the same job as a fuse.

True. A trip switch cuts off the current to a circuit when it becomes too high, just like a fuse does.

An appliance needs a current of 3.1 A. Should it be fitted with a 3 A, 5 A or 13 A fuse? Explain your answer.

A 5 A fuse. The fuse rating must be higher than the current needed, without being too high, so you should always choose the next size up .

Name the two factors that determine the amount of electrical energy an appliance transfers.

The time the appliance is switched on for, and the power of the appliance.

A 1 kW iron transfers the same amount of energy in one hour as a ______ iron transfers in 30 minutes.

A 1 kW iron transfers the same amount of energy in one hour as a 2 kW iron transfers in 30 minutes.

Describe the energy transfer that takes place in an electric heater.

Energy is transferred electrically from the mains supply to the thermal store of the heating element.

True or False? A 100 W heater run for 30 hours transfers the same amount of energy as a 3000 W heater run for 1 hour.

True. Energy transferred depends on both power and time , and 100 W × 30 hours gives the same amount of energy as 3000 W × 1 hour.

Define kilowatt-hour (kW h) .

The kilowatt-hour is a unit of energy equivalent to one kilowatt of power expended for one hour .

1 kilowatt-hour is equivalent to ______ joules.

1 kilowatt-hour is equivalent to 3.6 × 10⁶ joules.

What is the kilowatt-hour mainly used for?

The kilowatt-hour is a large unit of energy, used mainly to measure and compare energy usage in homes, businesses and factories .

O LevelPhysicsCambridge (CIE)Flashcards4. Electricity & Magnetism4.4 Practical Electricity

4.4 Practical Electricity (Cambridge (CIE) O Level Physics): Flashcards

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Cards in this collection (21)

Define fuse.
A fuse is a safety device that cuts off the flow of electricity to an appliance if the current becomes too large. It contains a thin wire that heats up and melts, breaking the circuit.
Define double insulation.
Double insulation means an appliance has two layers of insulation — insulation around the wires and a non-metallic case — so it cannot become electrified and does not need an earth wire.
Name three common electrical hazards found in the home.
Any three from: damaged insulation, overheating of cables, damp conditions, and excess current from overloaded plugs, extension leads or sockets.
State the frequency and potential difference of the UK mains electricity supply.
The UK mains supply has a frequency of 50 Hz and a potential difference of about 230 V.
Describe what happens if a live wire touches the metal case of an earthed appliance.
The earth wire provides a low resistance path to earth. This causes a surge of current in the earth wire and the live wire. The high current melts the fuse, breaking the circuit and cutting off the electricity supply, making the appliance safe.
Mains electricity in the UK is an ______ current supply, meaning the direction of current changes back and forth 50 times a second.
Mains electricity in the UK is an alternating current supply, meaning the direction of current changes back and forth 50 times a second.
True or False?
A trip switch performs the same job as a fuse.
True.
A trip switch cuts off the current to a circuit when it becomes too high, just like a fuse does.
An appliance needs a current of 3.1 A. Should it be fitted with a 3 A, 5 A or 13 A fuse? Explain your answer.
A 5 A fuse. The fuse rating must be higher than the current needed, without being too high, so you should always choose the next size up.
Define electrical energy transferred by an appliance.
The electrical energy transferred by an appliance is given by $E = V I t$ where E is energy in joules (J), V is potential difference in volts (V), I is current in amps (A) and t is time in seconds (s).
Name the two factors that determine the amount of electrical energy an appliance transfers.
The time the appliance is switched on for, and the power of the appliance.
A 1 kW iron transfers the same amount of energy in one hour as a ______ iron transfers in 30 minutes.
A 1 kW iron transfers the same amount of energy in one hour as a 2 kW iron transfers in 30 minutes.
Describe the energy transfer that takes place in an electric heater.
Energy is transferred electrically from the mains supply to the thermal store of the heating element.
True or False?
A 100 W heater run for 30 hours transfers the same amount of energy as a 3000 W heater run for 1 hour.
True.
Energy transferred depends on both power and time, and 100 W × 30 hours gives the same amount of energy as 3000 W × 1 hour.
Define electrical power.
Power is the rate of transfer of energy: $P = \frac{E}{t}$ where P is power in watts (W), E is energy in joules (J) and t is time in seconds (s).
State the equation linking electrical power, current and potential difference, defining each symbol.
$P = I V$ where P is power in watts (W), I is current in amps (A) and V is potential difference in volts (V).
State the two forms of the power equation that involve resistance, defining each symbol.
$P = I^{2} R$ and $P = \frac{V^{2}}{R}$ where P is power in watts (W), I is current in amps (A), V is potential difference in volts (V) and R is resistance in ohms (Ω).
True or False?
For a fixed resistor, doubling the current through it doubles the power dissipated.
False.
Since $P = I^{2} R$ , doubling the current makes the power four times as great, not double.
Define kilowatt-hour (kW h).
The kilowatt-hour is a unit of energy equivalent to one kilowatt of power expended for one hour.
1 kilowatt-hour is equivalent to ______ joules.
1 kilowatt-hour is equivalent to 3.6 × 10⁶ joules.
State the equation used to calculate energy in kilowatt-hours, defining each symbol.
$E = P t$ where E is energy in kilowatt-hours (kW h), P is power in kilowatts (kW) and t is time in hours (h). Note that this equation does not use S.I. units.
What is the kilowatt-hour mainly used for?
The kilowatt-hour is a large unit of energy, used mainly to measure and compare energy usage in homes, businesses and factories.

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