IGCSE Physics: The Electromagnetic Spectrum Practice Questions
The electromagnetic spectrum runs from radio waves through microwaves, infrared, visible light, ultraviolet and X-rays to gamma rays. All of them are transverse waves that travel at the same speed in a vacuum, approximately 3 x 108 m/s.
Sub-topic 3.3 of Cambridge IGCSE Physics 0625 rewards straightforward recall more than any other part of the course, and it also carries a wave equation calculation using standard form. The questions below cover the order, the uses, the dangers and the calculation.
What you need to know for The Electromagnetic Spectrum
- Order of the spectrumRadio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. Wavelength decreases and frequency increases from left to right.
- Common propertiesAll are transverse waves, all can travel through a vacuum, and all travel at approximately 3 x 108 m/s in a vacuum.
- Uses, part oneRadio waves for broadcasting and communications. Microwaves for satellite links, mobile phones and cooking. Infrared for remote controls, thermal imaging and short range communication.
- Uses, part twoVisible light for vision, photography and optical fibre communication. Ultraviolet for detecting forged banknotes and sterilising water. X-rays for medical imaging and security scanning. Gamma rays for sterilising equipment and treating cancer.
- DangersMicrowaves cause internal heating of body tissue. Infrared causes skin burns. Ultraviolet damages surface cells and causes skin cancer and eye damage. X-rays and gamma rays are ionising and cause mutation and cancer.
- Wave equation in standard formc = f x lambda. With c as 3 x 108 m/s, work in standard form throughout rather than writing out the zeros.
IGCSE Physics The Electromagnetic Spectrum questions and answers
4 exam-style questions written to the 0625 syllabus. Try each one on paper first, then open the worked answer to check your method against the marks.
List the seven regions of the electromagnetic spectrum in order of increasing frequency, and state which end has the longest wavelength.
Show the worked answer
- In order of increasing frequency: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
- Frequency and wavelength are inversely related, since c = f x lambda and c is constant.
- The radio wave end therefore has the longest wavelength and the lowest frequency.
- The gamma ray end has the shortest wavelength and the highest frequency, and is the most dangerous because it is the most strongly ionising.
A radio station broadcasts at a frequency of 100 MHz. Calculate the wavelength of the waves. Take the speed of electromagnetic waves as 3.0 x 108 m/s.
Show the worked answer
- Convert the frequency to hertz: 100 MHz = 100 x 106 = 1.0 x 108 Hz.
- Use c = f x lambda, rearranged to lambda = c divided by f.
- lambda = 3.0 x 108 divided by 1.0 x 108.
- lambda = 3.0 m.
State one use and one danger of ultraviolet radiation, and explain why sunscreen is recommended in Malaysia.
Show the worked answer
- A use: ultraviolet causes some inks and dyes to fluoresce, so it is used to check banknotes and security markings for forgery. Sterilising water and equipment is an equally acceptable answer.
- A danger: ultraviolet damages the DNA in surface skin cells, which can lead to mutation and skin cancer, and it also damages the eyes.
- Malaysia lies close to the equator, so the Sun is high in the sky and the ultraviolet intensity at ground level is high throughout the year.
- Sunscreen contains substances that absorb or reflect ultraviolet radiation before it reaches the skin cells, reducing the exposure and therefore the risk.
State two properties that all electromagnetic waves have in common, and explain why gamma rays are more hazardous than radio waves.
Show the worked answer
- Property 1: all electromagnetic waves are transverse waves.
- Property 2: all travel at the same speed in a vacuum, approximately 3 x 108 m/s. They can also all travel through a vacuum, which mechanical waves cannot.
- Gamma rays have a much higher frequency and therefore carry far more energy per wave than radio waves.
- That energy is enough to ionise atoms in living cells, damaging DNA and causing mutations that can lead to cancer. Radio waves carry too little energy per wave to ionise, so they pass through the body harmlessly.
Common mistakes in this topic
- Getting the order of the spectrum wrong, particularly around visible light.
- Forgetting to convert kHz, MHz or GHz to Hz before using the wave equation.
- Saying different electromagnetic waves travel at different speeds in a vacuum.
- Confusing the uses of infrared and ultraviolet.
- Describing microwaves as ionising. They cause heating, not ionisation.
Exam tips
- Memorise the seven regions with a mnemonic and always write them in the same direction, then state which end you started from.
- Work in standard form throughout. Writing out 300000000 invites errors.
- Learn one use and one danger for each region. That covers almost every version of the question.
- Only ultraviolet, X-rays and gamma rays are ionising. That single fact answers most hazard questions.
- Link the danger to the mechanism: heating for microwaves and infrared, ionisation and DNA damage for the high frequency end.
Practise 20 more questions like this, free
vStudyWise marks every answer instantly, tracks the topics you keep dropping marks on and turns them into a weekly study plan.
The Electromagnetic Spectrum FAQs
What is the order of the electromagnetic spectrum?
In order of increasing frequency and decreasing wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. Radio waves have the longest wavelength and lowest frequency, and gamma rays the shortest wavelength and highest frequency.
Do all electromagnetic waves travel at the same speed?
In a vacuum, yes. All electromagnetic waves travel at approximately 3 x 10 to the power 8 metres per second. They travel more slowly in materials, and different frequencies can slow by different amounts, which is why a prism splits white light into colours.
Why are gamma rays more dangerous than radio waves?
Gamma rays have a far higher frequency and therefore carry much more energy per wave. That energy is sufficient to ionise atoms in living cells, damaging DNA and causing mutations that can lead to cancer. Radio waves carry too little energy per wave to ionise anything.
What is the difference between infrared and ultraviolet?
Infrared sits just below red light in frequency and is associated with heating, thermal imaging and remote controls. Ultraviolet sits just above violet light, has a higher frequency and energy, is ionising, and is used for detecting forgeries and sterilising, but causes skin cancer with overexposure.
Continue through the IGCSE Physics syllabus
Related IGCSE Physics topics
See all 24 IGCSE Physics practice topics ›
Written to the published Cambridge IGCSE Physics (0625) syllabus. Check your school entry code and syllabus year, because Core and Extended candidates are assessed on different content. Last reviewed 2026-08-12.