OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Describe how, in different domestic devices, energy is transferred from…
Full specification wording
Power and efficiency: describe how, in different domestic devices, energy is transferred from batteries or the a.c. from the mains (to include: how energy may be wasted in the transfer to and within motors and heating devices)
Domestic devices take energy from a battery (chemical store) or from the mains a.c. supply and transfer it to other stores.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 3 of 8
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Domestic devices take energy from a battery (chemical store) or from the mains a.c. supply and transfer it to other stores. In a battery torch, chemical energy in the battery becomes electrical transfer along the wires and then light and thermal energy in the bulb; the thermal energy is wasted to the surroundings. In a mains kettle, the a.c. supply drives current through the heating element, transferring energy electrically to the element's thermal store, then to the water; some heats the kettle body and air. In a motor, such as a fan, electrical transfer becomes kinetic energy of the rotating parts, but friction in bearings and resistance heating in the coils waste energy as thermal energy. Identify the input store, the transfer pathway and the useful and wasted output stores for each device.
What earns the marks
- Identifies the battery as a store of chemical energy and the mains a.c. supply as the source of electrical transfer in domestic devices.
- Traces the pathway from source through wires or element to the useful output store, such as light in a torch or thermal energy in the water of a kettle.
- States that a motor transfers energy electrically to kinetic energy of the moving parts.
- Explains that friction in a motor's bearings and resistance heating in its coils waste energy as thermal energy to the surroundings.
- Explains that a heating device wastes energy by heating the device body and the surrounding air as well as the intended object.
Common mistakes and how to put them right
Treats energy as used up rather than transferred to other stores.
Put it right: State that energy is conserved and dissipated to the surroundings.
Names the battery as a source of electrical energy only.
Put it right: Describe it as a chemical store that transfers energy electrically.
Assumes a motor wastes no energy.
Put it right: Identify friction and resistance heating as sources of wasted thermal energy.
Claims a kettle transfers all its energy to the water.
Put it right: Note that some heats the kettle body and the air.
Exam tips
- For each device, name the input store, the transfer pathway and the useful and wasted output stores before choosing an option.
- Check whether the device is battery-powered or mains-powered, because the source store differs.
- Reject any option that says energy is destroyed or used up; energy is always conserved and may be dissipated.
- Look for the word 'wasted' and link it to thermal energy transferred to the surroundings.
Try the lesson
The start of the Power and efficiency: describe how, in different domestic devices, energy is transferred from batteries or the a.c. from the mains (to include: how energy may be wasted in the transfer to and within motors and heating devices) lesson, made from checked teaching notes for this specification point.
Have a go first
A battery-powered toy car moves across a floor. Which energy transfer is most direct from the battery to the car's movement?
Listen
Domestic devices take energy from a battery (chemical store) or from the mains a.c. supply and transfer it to other stores. In a battery torch, chemical energy in the battery becomes electrical transfer along the wires and then light and thermal energy in the bulb; the thermal energy is wasted to the surroundings. In a mains kettle, the a.c. supply drives current through the heating element, transferring energy electrically to the element's thermal store, then to the water; some heats the kettle body and air. In a motor, such as a fan, electrical transfer becomes kinetic energy of the rotating parts, but friction in bearings and resistance heating in the coils waste energy as thermal energy. Identify the input store, the transfer pathway and the useful and wasted output stores for each device. A strong answer earns marks for these points. Identifies the battery as a store of chemical energy and the mains a.c. supply as the source of electrical transfer in domestic devices. Traces the pathway from source through wires or element to the useful output store, such as light in a torch or thermal energy in the water of a kettle. States that a motor transfers energy electrically to kinetic energy of the moving parts. Explains that friction in a motor's bearings and resistance heating in its coils waste energy as thermal energy to the surroundings. Exam tip: For each device, name the input store, the transfer pathway and the useful and wasted output stores before choosing an option.
Key words
Say what each word means before you turn the card.
Battery as chemical store versus mains a.c. supply
Try answering aloud or in your head before turning the card.
Useful and wasted energy in motors
Try answering aloud or in your head before turning the card.
Wasted energy in heating devices
Try answering aloud or in your head before turning the card.
See every definition
- Battery as chemical store versus mains a.c. supply
- A battery is a store of chemical energy, while the mains a.c. supply is the source of electrical transfer in domestic devices.
- Useful and wasted energy in motors
- A motor transfers energy electrically to kinetic energy of the moving parts, but friction in bearings and resistance heating in the coils waste energy as thermal energy to the surroundings.
- Wasted energy in heating devices
- A heating device wastes energy by heating the device body and the surrounding air as well as the intended object.
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