AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Electromagnetic waves form a continuous spectrum and all types of…
Full specification wording
Types of electromagnetic waves: Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air.
Electromagnetic (EM) waves are oscillating electric and magnetic fields that transfer energy from a source to an absorber without needing a medium.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 2 of 5
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Electromagnetic (EM) waves are oscillating electric and magnetic fields that transfer energy from a source to an absorber without needing a medium. They form a continuous spectrum: there is no gap between radio waves and microwaves, or between infrared and visible light, because wavelength and frequency change smoothly. In a vacuum all EM waves travel at the same speed, about 3.0 × 10⁸ m/s. Through air the speed is almost identical, so air is treated as a vacuum. A useful method is to apply v = f λ: if v is fixed at 3.0 × 10⁸ m/s, then a wave with a higher frequency must have a shorter wavelength.
For example: A 100 MHz radio wave has λ = 3.0 m, while a 10¹⁵ Hz ultraviolet wave has λ = 3.0 × 10⁻⁷ m.
What earns the marks
- States that electromagnetic waves are transverse oscillations of electric and magnetic fields that transfer energy.
- Explains that the spectrum is continuous because wavelength and frequency vary smoothly with no gaps between adjacent groups.
- States that all EM waves travel at the same velocity in a vacuum, approximately 3.0 × 10⁸ m/s.
- States that the speed in air is effectively the same as in a vacuum for calculation purposes.
- Applies v = f λ to show that, at constant speed, frequency and wavelength are inversely proportional.
- Uses a numerical example, such as a radio wave and an ultraviolet wave, to compare wavelengths at the same speed.
Common mistakes and how to put them right
Thinking that different EM waves travel at different speeds in a vacuum.
Put it right by stating that speed is identical and only frequency and wavelength differ.
Believing that EM waves need a medium such as air to travel.
Put it right by explaining that they can cross a vacuum and air merely slows them very slightly.
Treating the spectrum as separate blocks with gaps.
Put it right by describing a continuous change in wavelength and frequency.
Exam tips
- Quote the speed of all EM waves in a vacuum as 3.0 × 10⁸ m/s and use it in v = f λ calculations.
- When comparing two EM waves, state explicitly that speed is constant so a longer wavelength means a lower frequency.
- Use the phrase continuous spectrum and refer to smooth changes in wavelength and frequency rather than listing groups only.
Try the lesson
The start of the Types of electromagnetic waves: Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement about the speed of electromagnetic waves in a vacuum is correct?
Listen
Electromagnetic (EM) waves are oscillating electric and magnetic fields that transfer energy from a source to an absorber without needing a medium. They form a continuous spectrum: there is no gap between radio waves and microwaves, or between infrared and visible light, because wavelength and frequency change smoothly. In a vacuum all EM waves travel at the same speed, about 3.0 × 10⁸ m/s. Through air the speed is almost identical, so air is treated as a vacuum. A useful method is to apply v = f λ: if v is fixed at 3.0 × 10⁸ m/s, then a wave with a higher frequency must have a shorter wavelength. For example, a 100 MHz radio wave has λ = 3.0 m, while a 10¹⁵ Hz ultraviolet wave has λ = 3.0 × 10⁻⁷ m. A strong answer earns marks for these points. States that electromagnetic waves are transverse oscillations of electric and magnetic fields that transfer energy. Explains that the spectrum is continuous because wavelength and frequency vary smoothly with no gaps between adjacent groups. States that all EM waves travel at the same velocity in a vacuum, approximately 3.0 × 10⁸ m/s. States that the speed in air is effectively the same as in a vacuum for calculation purposes. A common slip: Thinking that different EM waves travel at different speeds in a vacuum. Instead, stating that speed is identical and only frequency and wavelength differ. Exam tip: Quote the speed of all EM waves in a vacuum as 3.0 × 10⁸ m/s and use it in v = f λ calculations.
Key words
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Energy transfer by electromagnetic radiation
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The continuous nature of the electromagnetic spectrum
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Constant speed of electromagnetic waves in a vacuum
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See every definition
- Energy transfer by electromagnetic radiation
- Oscillating electric and magnetic fields transfer energy from a source to an absorber without needing a medium.
- The continuous nature of the electromagnetic spectrum
- There is no gap between adjacent groups because wavelength and frequency change smoothly.
- Constant speed of electromagnetic waves in a vacuum
- All types of electromagnetic wave travel at the same velocity through a vacuum or air.
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