1.8 Electrical Appliances

A free GCSE Physics lesson for AQA (8463) from OBA School: how energy reaches your home, what appliances are used for, useful and wasted transfers, and choosing an appliance. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe how energy is supplied to homes and explain why electrical appliances are so useful
• Identify the useful and wasted energy transfers in everyday electrical appliances
• Compare appliances using efficiency and choose the best one for a job
• Calculate the overall efficiency of a chain of energy transfers

Key words

• Electrical appliance: A device that uses an electric current to transfer energy for a purpose.
• Electric current: A flow of charge. It transfers energy; it is not an energy store.
• Mains electricity: The supply to homes from the National Grid (230 V in the UK).
• Overall efficiency: For a chain of transfers: the efficiencies of the stages multiplied together.
• Wind-up (clockwork) device: A device powered by a spring that the user winds up by hand.

Energy in the home

Most of the energy used in homes is supplied by electricity, gas and oil. Gas and oil are mainly used for heating and cooking. Electricity can do almost every job, and does it at the flick of a switch, which is why electrical appliances are everywhere.

An electric current is a flow of charge. As the charge flows through an appliance it transfers energy to it; the appliance then transfers the energy to the stores we want. Everyday appliances are used for:

• heating – kettle, toaster, oven, hairdryer
• lighting – lamps and screens
• making things move – anything with an electric motor: fan, drill, washing machine, blender
• producing sound and images – speakers, TVs, phones

Key fact: Electricity is not an energy store. It is a way of transferring energy, from a power station or a battery to an appliance.

Useful and wasted transfers

• LED desk lamp; Useful energy transfer light from the LEDs; Wasted energy transfer heating of the LEDs and lamp body
• Electric fan heater; Useful energy transfer heating the air blown into the room; Wasted energy transfer sound from the fan motor
• Washing machine; Useful energy transfer heating the water; kinetic store of the drum; Wasted energy transfer heating the motor and casing; sound and vibration
• Television; Useful energy transfer light from the screen; sound from the speakers; Wasted energy transfer heating of the electronics and screen
• Phone charger; Useful energy transfer chemical store of the phone battery; Wasted energy transfer heating of the charger and cable
• Vacuum cleaner; Useful energy transfer kinetic store of the air (suction); Wasted energy transfer heating of the motor; sound

Whether a transfer counts as useful depends on the job. In a fan heater, the motor gets warm – but that warms the air going into the room, so it is not wasted. In an LED lamp, the same heating would be wasted.

Choosing an appliance

An appliance is designed for one purpose and should waste as little energy as possible. When two appliances do the same job, the more efficient one wastes less energy and costs less to run.

Worked example: which lamp?

In one minute, lamp A is supplied with 600 J and gives out 90 J of light. Lamp B is supplied with 300 J and also gives out 90 J of light.
efficiency A = 90 ÷ 600 = 0.15 (15%); efficiency B = 90 ÷ 300 = 0.30 (30%)
Lamp B gives the same light while wasting 210 J per minute instead of 510 J.

Answer: choose lamp B – it is twice as efficient

Appliances without mains electricity

A wind-up (clockwork) radio or torch works where there is no mains supply and no batteries to buy. Turning the handle winds a spring, increasing its elastic potential store. As the spring unwinds, it turns a small generator, which produces a current.

Advantages: no batteries or mains needed; useful in remote areas or emergencies. Disadvantages: it must be wound up often; it can only supply a small power.

Chains of energy transfers

Energy often passes through several stages, and some is wasted at each one. The overall efficiency is the efficiencies of the stages multiplied together.

Worked example: a phone battery

Charging the battery is 90% efficient; the battery transfers energy to the phone with 75% efficiency.
overall efficiency = 0.90 × 0.75 = 0.675 = 67.5%
percentage wasted = 100% − 67.5% = 32.5%

Answer: 67.5% overall

Exam tip: Do not add or average the efficiencies of the stages. Multiply them (as decimals).

Common mistakes

• Calling electricity an energy store, or saying a battery stores “electrical energy”.
• Saying an appliance “uses up” energy. It transfers it, mostly ending up in the surroundings.
• Adding the efficiencies of two stages instead of multiplying them.
• Saying any heating is wasted. In a kettle, toaster or heater, heating is the useful transfer.

Revision questions

Try these, then check your answers below each one.

Question 1. Which statement about electricity is correct? (Choose from: It is a flow of charge that transfers energy., It is an energy store., It is a type of fuel., It is stored in the wires of a house..)

Answer: It is a flow of charge that transfers energy.

Working: An electric current is a flow of charge. It transfers energy between stores; it is not a store itself.

Question 2. A battery is charged with 80% efficiency and then transfers energy to a laptop with 60% efficiency. Calculate the overall percentage efficiency.

Answer: 48 %

Working: 0.80 × 0.60 = 0.48 = 48%.

Question 3. True or false? An appliance should be chosen so that it wastes as little energy as possible for its job.

Answer: True

Working: True. Wasting less energy means a higher efficiency, lower running costs and less fuel used.

Related lessons

• Previous lesson: 1.6–1.7 Energy Dissipation and Efficiency
• Next lesson: 1.9 Energy and Power
• In this chapter: 1.1 Changes in Energy Stores
• In this chapter: 1.2 Conservation of Energy
• In this chapter: 1.3 Energy and Work

Continue in the full course

This lesson is section 1.8 (AGCPH0108) of our free GCSE Physics course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Physics course.