X-rays are used for medical imaging because they penetrate soft tissue but are absorbed by dense materials like bone. Free GCSE Physics notes and 12 FAQs.
Updated 23 Mar 2026 · Revise Right Team
Visible Light, Ultraviolet, X-Rays, and Gamma Rays is part of Light rays, lenses and electromagnetic waves in GCSE Edexcel Higher Physics.
6 min
Reading time
19
Lessons in this topic
GCSE Edexcel Higher
Pathway
Reviewed by Revise Right
Content review
What this lesson covers
X-rays are used for medical imaging because they penetrate soft tissue but are absorbed by dense materials like bone. Free GCSE Physics notes and 12 FAQs.
Explain how visible light is used in fibre optic communications
Describe the applications of ultraviolet radiation in energy efficient lamps and sun tanning
Compare the uses of X-rays and gamma rays in medical imaging and treatments
Evaluate why specific electromagnetic waves are suitable for their practical applications
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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.
Topic 5: Light and the electromagnetic spectrum
Light rays, lenses and electromagnetic waves
GCSE Edexcel Higher Physics
Revision notes
Read the core explanations from Visible Light, Ultraviolet, X-Rays, and Gamma Rays before testing yourself from memory.
1. The Electromagnetic Spectrum in Action
You use electromagnetic waves every second of your life without realising it. The light hitting your eyes right now, the WiFi connecting your phone, even the heat from your radiator - they're all part of the same electromagnetic family.
Today we're focusing on four specific members of this family: visible light, ultraviolet, X-rays, and gamma rays. Each one has unique properties that make it perfect for specific jobs in the modern world.
The key insight is this: as frequency increases across the spectrum, the waves carry more energy. This extra energy opens up new possibilities - but also new dangers.
All electromagnetic waves travel at the speed of light in a vacuum (3.0 × 10⁸ m/s). What changes across the spectrum is their frequency and wavelength - and this determines what they can do.
2. Visible Light - The Information Highway
Visible light sits right in the middle of the electromagnetic spectrum - not too energetic, not too weak. This makes it perfect for carrying information without damaging what it travels through.
The breakthrough application is fibre optic communications. Instead of sending electrical signals down copper wires, we send pulses of light down incredibly thin glass fibres. Each pulse represents digital data - a 1 or a 0.
Here's why visible light is perfect for this job. Glass is transparent to visible light, so the signal can travel for kilometres without significant loss. The light bounces off the inner walls of the fibre through total internal reflection, keeping the signal contained.
Compare this to electrical signals in copper wires, which lose energy as heat due to resistance. Fibre optics can carry much more data over much longer distances with less signal degradation.
3. Ultraviolet Radiation - Energy and Effects
Ultraviolet radiation has higher frequency than visible light, which means higher energy per photon. This extra energy creates new possibilities - and new risks.
Energy efficient lamps use UV radiation in a clever way. Inside the lamp, an electric current excites mercury vapour, which emits UV light. This UV then hits a phosphor coating on the inside of the bulb.
The phosphor absorbs the high-energy UV photons and re-emits the energy as lower-energy visible light photons. This process is much more efficient than heating a filament until it glows, which is how old incandescent bulbs work.
Sun tanning is UV's effect on human skin. UV photons have enough energy to trigger chemical reactions in skin cells, causing them to produce more melanin pigment. This is actually a protective response - the melanin absorbs UV to prevent DNA damage.
The danger is that too much UV can overwhelm this protection, causing sunburn and potentially skin cancer. This is why UV is classified as potentially harmful radiation.
4. X-rays and Gamma Rays - Medical Powerhouses
X-rays and gamma rays are the high-energy end of the electromagnetic spectrum. Their photons carry so much energy they can ionise atoms - removing electrons and creating charged particles.
This ionising ability makes them dangerous to living tissue, but also incredibly useful in medicine. The key is controlling the dose - enough to be useful, not enough to cause significant harm.
X-rays are perfect for medical imaging because they can penetrate soft tissue but are absorbed by dense materials like bone. When you have an X-ray, the rays pass through your body onto a detector. Bones show up as white shadows because they've absorbed the X-rays.
Gamma rays have even higher energy than X-rays. In medicine, this makes them excellent for cancer treatment. Gamma rays can be focused precisely on tumours, where their high energy destroys cancer cells by damaging their DNA beyond repair.
The challenge with both X-rays and gamma rays is minimising exposure to healthy tissue. Modern techniques use computer-controlled beams that can target diseased areas while avoiding healthy organs.
5. Why Each Wave Fits Its Job
The electromagnetic spectrum is like a toolkit - each type of wave is the right tool for specific jobs. Understanding why requires thinking about energy, penetration, and interaction with matter.
Visible light works for fibre optics because it has just the right energy. Too low (like radio waves) and you can't create sharp, distinct pulses. Too high (like UV) and the glass would absorb the signal or the energy would damage the fibre.
UV is perfect for energy efficient lamps because its photons have enough energy to excite phosphor atoms but not so much that they'd destroy the coating. It's also invisible, so all the visible light you see comes from the phosphor conversion.
X-rays excel at imaging because they can penetrate soft tissue but are stopped by dense bone. Lower energy waves like visible light can't penetrate at all. Higher energy gamma rays would go straight through everything, giving no contrast.
Gamma rays are ideal for cancer treatment precisely because they're so energetic. They can destroy the DNA in cancer cells completely. The challenge is delivering this destructive power only where it's needed.
6. Exam Success - Getting Full Marks
Exam questions on electromagnetic waves often ask you to explain why a particular wave is suitable for its application. The examiners want to see that you understand the link between wave properties and practical uses.
For 'explain' questions, always structure your answer as: property → because → effect. For example: 'X-rays can penetrate soft tissue because they have high energy, so they can pass through skin and muscle to reach bones.'
Watch out for the common mistake of confusing X-rays and gamma rays. Both are ionising, but X-rays are typically used for imaging (because they can penetrate some materials but not others) while gamma rays are used for treatment (because they have even higher energy).
When discussing safety, always mention that ionising radiation requires careful control of exposure. Don't just say 'it's dangerous' - explain that the risk comes from the high energy that can damage living cells.
Worked example: Worked Method: Visible Light, Ultraviolet, X-Rays, and Gamma Rays
Use the relevant formula, substitute values with units, calculate, then state the final answer clearly.
Write down the correct physics formula. — Write down the correct physics formula.
Substitute known values with units. — Substitute known values with units.
Rearrange if needed and calculate carefully. — Rearrange if needed and calculate carefully.
Give the final answer with correct unit and sensible precision. — Give the final answer with correct unit and sensible precision.
Answer: Final answer should include unit and appropriate significant figures.
Sources and content standards
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-23.
Melanin is a pigment that skin cells produce in response to UV, absorbing UV to prevent DNA damage. This protective response is sun tanning, but too much UV can overwhelm it, causing sunburn and potentially skin cancer.
Why is visible light used in fibre optics?
Visible light is used in fibre optic communications because glass is transparent to it, so pulses of light can travel for kilometres without significant loss. The light bounces off the inner walls of the fibre by total internal reflection, keeping the signal contained.
How do energy efficient lamps use ultraviolet?
In an energy efficient lamp, an electric current excites mercury vapour, which emits UV light. The UV hits a phosphor coating inside the bulb, which absorbs it and re-emits the energy as visible light, which is much more efficient than heating a filament.
How does UV cause sun tanning?
UV photons have enough energy to trigger chemical reactions in skin cells, causing them to produce more melanin pigment, which absorbs UV to prevent DNA damage. Too much UV overwhelms this protection, causing sunburn and potentially skin cancer.
Why are X-rays used for medical imaging?
X-rays are used for medical imaging because they penetrate soft tissue but are absorbed by dense materials like bone. The rays pass through the body onto a detector, and bones show up as white shadows because they have absorbed the X-rays.
How are gamma rays used to treat cancer?
Gamma rays are used to treat cancer because their very high energy destroys cancer cells by damaging their DNA beyond repair. They can be focused precisely on tumours, and computer-controlled beams help avoid healthy organs.
What is the difference between how X-rays and gamma rays are used?
X-rays are typically used for medical imaging because they penetrate soft tissue but are stopped by bone, while gamma rays are used for cancer treatment because they have even higher energy. Both are ionising, so exposure must be carefully controlled.
Why do bones show up white on X-rays?
Bones show up as white shadows on X-rays because they absorb the X-rays, while soft tissue lets the X-rays pass through onto the detector. Dense materials like bone stop X-rays, giving contrast in the image.
Why are optical fibres better than copper wires?
Glass fibres can carry much more data over much longer distances with less signal loss than copper wires. Electrical signals in copper lose energy as heat due to resistance, while light in glass fibres travels kilometres without significant loss.
How is data sent through optical fibres?
Data is sent through glass fibres as pulses of visible light, with each pulse representing a 1 or a 0. The light bounces off the inner walls of the thin glass fibre by total internal reflection, keeping the signal contained.
Why are X-ray doses limited?
X-ray doses are kept low because X-rays are ionising and their high energy can damage living cells. The dose must be enough to be useful but not enough to cause significant harm, and modern beams target diseased areas while avoiding healthy organs.
What does the phosphor coating in an energy efficient lamp do?
The phosphor coating inside an energy efficient lamp absorbs high-energy UV photons and re-emits the energy as lower-energy visible light photons. The UV comes from mercury vapour excited by an electric current.