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From lowest to highest frequency, the EM spectrum is radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Free notes.
The Electromagnetic Spectrum is part of Light rays, lenses and electromagnetic waves in GCSE Edexcel Higher Physics.
5 min
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GCSE Edexcel Higher
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From lowest to highest frequency, the EM spectrum is radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Free notes.
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Use this lesson to stay inside Light rays, lenses and electromagnetic waves while connecting the detail back to the wider Topic 5: Light and the electromagnetic spectrum topic.
Read the core explanations from The Electromagnetic Spectrum before testing yourself from memory.
Right now, invisible waves are passing through your body. Radio signals from stations across the country, microwaves from mobile phone towers, infrared heat from warm objects, ultraviolet light from the sun, and even gamma rays from distant stars.
Yet your eyes can only detect a tiny fraction of these waves - the narrow band we call visible light. It's like being able to hear only one note on a piano that has thousands of keys.
All these invisible waves belong to the electromagnetic spectrum. Understanding this spectrum helps explain everything from why we get sunburnt to how doctors can see inside our bodies without cutting us open.
All electromagnetic waves share three key properties. They all travel at the same speed in a vacuum - 300,000,000 metres per second (the speed of light). They can all travel through empty space, unlike sound waves which need matter to travel through.
What makes them different is their wavelength and frequency. Think of wavelength as the distance between wave peaks - like the distance between ripples on a pond. Frequency is how many waves pass a point each second.
Here's the crucial relationship: waves with longer wavelengths have lower frequencies, and waves with shorter wavelengths have higher frequencies. It's an inverse relationship - as one increases, the other decreases.
The electromagnetic spectrum is like a rainbow that extends far beyond what we can see. Starting with the longest wavelengths and lowest frequencies, we have: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
Radio waves can be kilometres long - imagine a wave stretching from your house to the next town. At the other extreme, gamma rays have wavelengths smaller than the nucleus of an atom. That's a range covering more than 20 orders of magnitude.
Each type of wave has different properties and uses. Radio waves easily pass through buildings, which is why your radio works indoors. X-rays can penetrate soft tissue but are absorbed by bones, making them perfect for medical imaging.
The higher the frequency (shorter the wavelength), the more energy the wave carries. This explains why gamma rays are dangerous to living tissue whilst radio waves are harmless - gamma rays pack millions of times more energy per wave.
Your eyes contain special cells called photoreceptors that can only respond to a tiny slice of the electromagnetic spectrum. This visible light ranges from red (wavelength about 700 nanometres) to violet (wavelength about 400 nanometres).
Within visible light, different wavelengths appear as different colours. Red light has the longest wavelength, followed by orange, yellow, green, blue, indigo, and violet with the shortest wavelength. Remember the order with the mnemonic 'Roy G. Biv'.
Evolution shaped our eyes to detect visible light because this is the range of electromagnetic radiation that the Sun emits most strongly. It's also the range that passes most easily through Earth's atmosphere and through water.
Many animals can see beyond our visible range. Bees can see ultraviolet patterns on flowers that guide them to nectar. Snakes can detect infrared radiation from warm-blooded prey. We've had to build special instruments to 'see' these invisible parts of the spectrum.
Each part of the electromagnetic spectrum has found important applications in modern technology. Radio waves carry radio and TV signals across vast distances. Microwaves heat food by making water molecules vibrate rapidly.
Infrared radiation is what we feel as heat from the Sun or a fire. Thermal imaging cameras detect infrared to show heat patterns. Ultraviolet light kills bacteria, making it useful for sterilisation, but too much UV damages skin cells and causes cancer.
X-rays penetrate soft tissue but are absorbed by dense materials like bone, making them perfect for medical imaging. However, X-rays can damage cells, so exposure must be limited. Gamma rays are used to sterilise medical equipment and treat cancer, but they're extremely dangerous.
The general rule is: the higher the frequency, the more energy per wave, and the more dangerous to living tissue. This is why we worry about UV, X-rays, and gamma rays, but not about radio waves or visible light at normal intensities.
Exam questions often test whether you can recall the correct order of electromagnetic waves. The key is remembering that as wavelength decreases, frequency increases. Start with radio waves (longest wavelength, lowest frequency) and work towards gamma rays (shortest wavelength, highest frequency).
Questions frequently ask about the limited range of human vision. Remember that our eyes detect only visible light - a tiny fraction of the full electromagnetic spectrum. This limitation exists because our eyes evolved to detect the wavelengths that the Sun emits most strongly.
When comparing different electromagnetic waves, focus on the inverse relationship between wavelength and frequency. Longer wavelengths always mean lower frequencies, and shorter wavelengths always mean higher frequencies. This relationship helps explain why gamma rays are more dangerous than radio waves.
Worked example: Worked Method: The Electromagnetic Spectrum
Use the relevant formula, substitute values with units, calculate, then state the final answer clearly.
Answer: Final answer should include unit and appropriate significant figures.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-23.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Visible light ranges from red, with a wavelength of about 700 nanometres, to violet, with a wavelength of about 400 nanometres. This is the narrow range of electromagnetic waves human eyes can detect.
From longest wavelength and lowest frequency to shortest wavelength and highest frequency, the electromagnetic spectrum is: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
Radio waves carry radio and TV signals, microwaves heat food, infrared is used in thermal imaging cameras, ultraviolet kills bacteria for sterilisation, X-rays are used for medical imaging, and gamma rays sterilise medical equipment and treat cancer.
Wavelength and frequency are inversely related: waves with longer wavelengths have lower frequencies, and waves with shorter wavelengths have higher frequencies. As one increases, the other decreases.
Gamma rays are more dangerous because the higher the frequency, the more energy each wave carries. Gamma rays have the highest frequency and pack millions of times more energy per wave than radio waves, which are harmless.
Gamma rays have the highest frequency and shortest wavelength in the electromagnetic spectrum, smaller than the nucleus of an atom. They carry the most energy per wave, making them highly penetrating and dangerous.
Red light has the longest wavelength of visible light, followed by orange, yellow, green, blue, indigo and violet, which has the shortest. The order can be remembered with the mnemonic Roy G. Biv.
Photoreceptors are special cells in the eyes that can only respond to a tiny slice of the electromagnetic spectrum: visible light. Eyes evolved to detect the wavelengths the Sun emits most strongly.
Radio waves have the longest wavelength and lowest frequency in the electromagnetic spectrum. Their wavelengths can be kilometres long, and they easily pass through buildings.
Thermal imaging cameras detect infrared radiation to show heat patterns. Infrared radiation is what is felt as heat from the Sun or a fire.
We can only see visible light because the photoreceptors in our eyes respond only to that narrow band, from red (about 700 nanometres) to violet (about 400 nanometres). Our eyes evolved to detect the wavelengths the Sun emits most strongly, which also pass easily through the atmosphere.
Bees can see ultraviolet patterns on flowers that guide them to nectar, beyond the human visible range. Snakes can also detect infrared radiation from warm-blooded prey.
Too much ultraviolet light damages skin cells and causes cancer, because UV has a higher frequency and more energy per wave than visible light. UV is also useful because it kills bacteria, for sterilisation.