IGCSE Physics / The electromagnetic spectrum
The electromagnetic spectrum revision notes
Edexcel International GCSE Physics (4PH1), chapter 11: The electromagnetic spectrum, specification point 3.10, 3.11. Free lesson.
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The electromagnetic spectrum is the continuous range of electromagnetic waves, from radio waves to gamma rays. Knowing the order and the properties shared by all electromagnetic waves helps you compare them accurately.
How the electromagnetic groups are ordered
The electromagnetic spectrum is one continuous range, so there are no gaps between its groups. Moving from radio waves towards gamma rays, the wavelength gets shorter and the frequency gets higher. The groups from longest to shortest wavelength are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Remember the order with: Rich Mice In Vans Use X-ray Goggles.
How radio waves and gamma rays compare
Radio waves and gamma rays are at opposite ends of the spectrum. They differ in wavelength and frequency, but not in their speed in a vacuum. When you give a difference, state which wave has the higher or lower value. Radio waves have the longest wavelength and lowest frequency. Gamma rays have the shortest wavelength and highest frequency. Both travel at 3 × 10⁸ m/s in a vacuum and are transverse waves.
What all electromagnetic waves share
Every electromagnetic wave travels at the same speed in a vacuum, whether it is a radio wave or a gamma ray. They are also all transverse waves. A vacuum is empty space. The shared speed is 3 × 10⁸ m/s. Gamma rays do not travel faster than radio waves. Their frequency and wavelength are different, but their speed in a vacuum is the same.
The colours in visible light
Visible light is the part of the electromagnetic spectrum that your eyes can detect. Its colours go from red, with the longest wavelength, to violet, with the shortest. The order is red, orange, yellow, green, blue, indigo, violet. Red has the longest wavelength and violet has the shortest.
How to state a difference clearly
Saying that two waves have different frequencies does not show which is higher. Give the direction of the difference so your answer shows the order. For example: X-rays have a higher frequency than microwaves and a shorter wavelength.