OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Explain that electromagnetic waves transfer energy from source to absorber…
Full specification wording
The electromagnetic spectrum: explain that electromagnetic waves transfer energy from source to absorber (to include: examples from a range of electromagnetic waves)
All electromagnetic (EM) waves carry energy and transfer it from a source to an absorber.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 2 of 9
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
All electromagnetic (EM) waves carry energy and transfer it from a source to an absorber. The source emits the wave; the wave travels (through a vacuum or a medium) and the absorber gains the energy. Examples across the spectrum: a hot filament or the Sun emits visible light, which is absorbed by a black surface and warms it; a microwave oven's magnetron emits microwaves absorbed by water molecules in food, heating it; infrared from a heater is absorbed by skin, warming it; ultraviolet from the Sun is absorbed by skin, causing tanning or sunburn; X-rays from an X-ray tube are absorbed by bone and detected on a film or sensor. In each case the key idea is energy moving from source to absorber, not matter moving.
What earns the marks
- States that electromagnetic waves transfer energy from a source to an absorber.
- Identifies a named EM wave and a named source that emits it.
- Identifies a named absorber that gains energy from that wave.
- Explains that energy, not matter, travels from source to absorber.
- Gives a correct example from a range of EM waves, such as infrared from a heater warming skin.
Common mistakes and how to put them right
Confuses energy transfer with matter transfer.
Put it right: State that the wave carries energy while no material travels with it.
Names a wave without a source or absorber.
Put it right: Give both a source and an absorber for the example.
Assumes only visible light transfers energy.
Put it right: Include examples from other EM waves such as microwaves or infrared.
Exam tips
- For each example, name the source, the wave and the absorber in one sentence.
- Use the phrase 'energy is transferred from source to absorber' to show the mechanism.
- Choose examples from at least two different regions of the EM spectrum to show range.
Try the lesson
The start of the The electromagnetic spectrum: explain that electromagnetic waves transfer energy from source to absorber (to include: examples from a range of electromagnetic waves) lesson, made from checked teaching notes for this specification point.
Have a go first
A radio station's transmitter sends radio waves that are picked up by a car radio aerial. What is transferred from the transmitter to the aerial?
Listen
All electromagnetic (EM) waves carry energy and transfer it from a source to an absorber. The source emits the wave; the wave travels (through a vacuum or a medium) and the absorber gains the energy. Examples across the spectrum: a hot filament or the Sun emits visible light, which is absorbed by a black surface and warms it; a microwave oven's magnetron emits microwaves absorbed by water molecules in food, heating it; infrared from a heater is absorbed by skin, warming it; ultraviolet from the Sun is absorbed by skin, causing tanning or sunburn; X-rays from an X-ray tube are absorbed by bone and detected on a film or sensor. In each case the key idea is energy moving from source to absorber, not matter moving. A strong answer earns marks for these points. States that electromagnetic waves transfer energy from a source to an absorber. Identifies a named EM wave and a named source that emits it. Identifies a named absorber that gains energy from that wave. Explains that energy, not matter, travels from source to absorber. Exam tip: For each example, name the source, the wave and the absorber in one sentence.
Key words
Say what each word means before you turn the card.
Energy transfer by waves
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Source and absorber
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Range of electromagnetic waves
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Energy versus matter
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See every definition
- Energy transfer by waves
- Electromagnetic waves carry energy and transfer it from a source to an absorber, while no material travels with the wave.
- Source and absorber
- The source emits the wave, the wave travels through a vacuum or a medium, and the absorber gains the energy.
- Range of electromagnetic waves
- Examples across the spectrum include visible light, microwaves, infrared, ultraviolet and X-rays, each transferring energy from a source to an absorber.
- Energy versus matter
- The key idea is energy moving from source to absorber, not matter moving.
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