AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Energy transfers in everyday appliances: Everyday electrical appliances are designed to bring about energy transfers.
Everyday electrical appliances transfer energy from one store to another to perform useful functions.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Everyday electrical appliances transfer energy from one store to another to perform useful functions. For example, a kettle transfers energy electrically from the mains supply to the thermal store of the water. A lamp transfers energy electrically, which is then transferred to the surroundings by light and heating pathways, ultimately increasing the thermal store of the surroundings. Appliances are designed so that the intended energy transfer is maximised and unwanted transfers are minimised. The power rating of an appliance tells us the rate at which it transfers energy, and the total energy transferred can be calculated using E = P × t, where E is energy in joules, P is power in watts and t is time in seconds.
What earns the marks
- Identify the useful energy transfer in a named everyday appliance, such as a kettle transferring energy electrically to a thermal store.
- Describe at least one unwanted energy transfer in an appliance, such as a lamp heating the surroundings.
- State that power is the rate of energy transfer and use the equation E = P × t.
- Explain how an appliance is designed to maximise useful energy transfer and minimise wasted energy.
- Compare the efficiency of appliances by considering useful output energy as a proportion of total input energy.
Common mistakes and how to put them right
Saying that energy is 'used up' or 'lost' rather than transferred to less useful stores.
Put it right: Energy is conserved and transferred to other stores, often the thermal store of the surroundings.
Confusing power and energy, for example using watts for energy.
Put it right: Power is measured in watts (W) and energy in joules (J); use E = P × t to link them.
Referring to light as an energy store.
Put it right: Light is a transfer pathway (radiation), not a store; energy transferred by light ultimately increases the thermal store of the surroundings.
Exam tips
- Name the appliance and state the useful energy transfer using the correct stores and pathways, for example 'from the chemical store of a battery, transferred electrically to the thermal store of the water'.
- When calculating energy transferred, convert time to seconds and power to watts before multiplying.
- Use the idea of efficiency to explain why some appliances waste less energy, referring to the proportion of energy usefully transferred.
Try the lesson
The start of the Energy transfers in everyday appliances: Everyday electrical appliances are designed to bring about energy transfers. lesson, made from checked teaching notes for this specification point.
Have a go first
Which everyday electrical appliance is designed mainly to transfer energy to the thermal store of the surroundings?
Listen
Everyday electrical appliances transfer energy from one store to another to perform useful functions. For example, a kettle transfers energy electrically from the mains supply to the thermal store of the water. A lamp transfers energy electrically, which is then transferred to the surroundings by light and heating pathways, ultimately increasing the thermal store of the surroundings. Appliances are designed so that the intended energy transfer is maximised and unwanted transfers are minimised. The power rating of an appliance tells us the rate at which it transfers energy, and the total energy transferred can be calculated using E = P × t, where E is energy in joules, P is power in watts and t is time in seconds. A strong answer earns marks for these points. Identify the useful energy transfer in a named everyday appliance, such as a kettle transferring energy electrically to a thermal store. Describe at least one unwanted energy transfer in an appliance, such as a lamp heating the surroundings. State that power is the rate of energy transfer and use the equation E = P × t. Explain how an appliance is designed to maximise useful energy transfer and minimise wasted energy. A common slip: Saying that energy is 'used up' or 'lost' rather than transferred to less useful stores. Instead, energy is conserved and transferred to other stores, often the thermal store of the surroundings. Exam tip: Name the appliance and state the useful energy transfer using the correct stores and pathways, for example 'from the chemical store of a battery, transferred electrically to the thermal store of the water'.
Key words
Say what each word means before you turn the card.
Power
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Efficiency
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Energy transfer
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E = P × t
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See every definition
- Power
- The rate at which an appliance transfers energy, measured in watts.
- Efficiency
- Useful output energy as a proportion of total input energy, explaining why some appliances waste less energy.
- Energy transfer
- Movement of energy from one store to another, as when a kettle transfers energy electrically to the thermal store of the water.
- E = P × t
- Equation used to calculate the total energy transferred, where E is energy in joules, P is power in watts and t is time in seconds.
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