IGCSE Physics 3.3 Electromagnetic Spectrum MCQs – 30 Practice Questions with Answers (Cambridge 0625)

Free practice MCQs for Cambridge IGCSE Physics (0625) Section 3.3, the Electromagnetic Spectrum, covering Core material plus Supplement questions where tagged. Work through each question, then open the Show Answer toggle to check the explanation.

Formula recap: v = f × λ, and every electromagnetic wave travels at 3.0 × 108 m/s in a vacuum. The spectrum order (longest wavelength first) is: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Need the full revision sheet? See the IGCSE Physics Formula Sheet.

The Spectrum – Order & Properties

Q1. Which list gives the electromagnetic waves in order, from longest wavelength to shortest wavelength?

  • (A) gamma, X-ray, ultraviolet, visible, infrared, microwave, radio
  • (B) radio, microwave, infrared, visible, ultraviolet, X-ray, gamma
  • (C) radio, infrared, microwave, visible, X-ray, ultraviolet, gamma
  • (D) visible, infrared, microwave, radio, ultraviolet, X-ray, gamma
Show Answer

Answer: B – Wavelength decreases steadily across the spectrum: radio waves are the longest (some are kilometres long) and gamma rays are the shortest. Option A is the exact reverse order, which is the order of increasing frequency.

Q2. Which electromagnetic wave has the highest frequency?

  • (A) radio waves
  • (B) ultraviolet
  • (C) gamma rays
  • (D) microwaves
Show Answer

Answer: C – All EM waves travel at the same speed in a vacuum, so the wave with the shortest wavelength has the highest frequency. Gamma rays have the shortest wavelength, so they have the highest frequency.

Q3. What is the speed of electromagnetic waves in a vacuum?

  • (A) 3.0 × 108 m/s
  • (B) 3.0 × 105 m/s
  • (C) 340 m/s
  • (D) It is different for each type of wave
Show Answer

Answer: A – Every member of the electromagnetic spectrum, from radio waves to gamma rays, travels at 3.0 × 108 m/s in a vacuum. 340 m/s is the approximate speed of sound in air, which is a common trap.

Q4. Which statement about all electromagnetic waves is correct?

  • (A) They are longitudinal waves
  • (B) They need a material medium to travel
  • (C) They carry no energy
  • (D) They are transverse waves and can travel through a vacuum
Show Answer

Answer: D – Electromagnetic waves are transverse waves made of oscillating electric and magnetic fields. They transfer energy and do not need a medium, which is how light and heat reach us from the Sun through empty space.

Q5. A radio station broadcasts on a frequency of 100 MHz (1.0 × 108 Hz). What is the wavelength of the radio waves?

  • (A) 0.30 m
  • (B) 30 m
  • (C) 3.0 m
  • (D) 3.0 × 106 m
Show Answer

Answer: C – Use λ = v ÷ f = (3.0 × 108) ÷ (1.0 × 108) = 3.0 m.

Q6. Microwaves used in a microwave oven have a wavelength of 3.0 cm (0.030 m). What is their frequency?

  • (A) 1.0 × 108 Hz
  • (B) 1.0 × 1010 Hz
  • (C) 9.0 × 109 Hz
  • (D) 1.0 × 106 Hz
Show Answer

Answer: B – First convert the wavelength: 3.0 cm = 0.030 m. Then f = v ÷ λ = (3.0 × 108) ÷ 0.030 = 1.0 × 1010 Hz. Forgetting to convert cm to m gives the wrong powers of ten in the other options.

Q7. Within the visible part of the spectrum, which colour of light has the longest wavelength and which has the shortest?

  • (A) Longest: red; shortest: violet
  • (B) Longest: violet; shortest: red
  • (C) Longest: green; shortest: red
  • (D) Longest: red; shortest: yellow
Show Answer

Answer: A – Visible light runs from red (longest wavelength, about 700 nm) through orange, yellow, green and blue to violet (shortest wavelength, about 400 nm).

Q8. Moving across the electromagnetic spectrum from radio waves towards gamma rays, the wavelength decreases. What happens to the frequency?

  • (A) It decreases
  • (B) It stays the same
  • (C) It first increases, then decreases
  • (D) It increases
Show Answer

Answer: D – In a vacuum the speed is constant, and v = f × λ. If λ decreases, f must increase so that the product stays equal to 3.0 × 108 m/s.

Q9. Which statement correctly compares two different electromagnetic waves travelling in a vacuum?

  • (A) The one with the longer wavelength travels faster
  • (B) They travel at the same speed, but the one with the shorter wavelength has the higher frequency
  • (C) The one with the higher frequency travels slower
  • (D) They have the same wavelength but different frequencies
Show Answer

Answer: B – All EM waves have the same speed in a vacuum (3.0 × 108 m/s). The members of the spectrum differ only in wavelength and frequency, linked by v = f × λ.

Q10. An electromagnetic wave has a frequency of 6.0 × 1014 Hz. To which part of the spectrum does it belong?

  • (A) infrared
  • (B) ultraviolet
  • (C) visible light
  • (D) microwave
Show Answer

Answer: C – λ = v ÷ f = (3.0 × 108) ÷ (6.0 × 1014) = 5.0 × 10−7 m = 500 nm, which lies inside the visible range (about 400 nm to 700 nm). Infrared wavelengths are longer than this and ultraviolet wavelengths are shorter.

Uses of Each Band

Q11. Communications satellites use one band of the spectrum because its waves can pass through the Earth’s atmosphere and be sent over long distances. Which band is used?

  • (A) microwaves
  • (B) infrared
  • (C) ultraviolet
  • (D) X-rays
Show Answer

Answer: A – Microwaves are used for satellite and mobile phone communication because they can travel through the atmosphere to reach satellites and can carry a large amount of information.

Q12. In a microwave oven, food cooks because the waves are absorbed by water molecules in the food, making the molecules vibrate faster. Which waves are used?

  • (A) radio waves
  • (B) infrared
  • (C) ultraviolet
  • (D) microwaves
Show Answer

Answer: D – Microwave ovens use microwaves at a frequency that water (and fat) molecules absorb strongly. The molecules gain kinetic energy, so the food heats up. Infrared also heats food, but in grills and toasters, not in microwave ovens.

Q13. The handset of a television remote control sends signals to the television using which type of radiation?

  • (A) ultraviolet
  • (B) infrared
  • (C) microwaves
  • (D) radio waves
Show Answer

Answer: B – Remote controls use pulses of infrared radiation. The same band is used in short-range optical links and some burglar alarm sensors.

Q14. Firefighters use thermal-imaging cameras to see hot objects and trapped people through smoke. Which radiation do these cameras detect?

  • (A) X-rays
  • (B) visible light
  • (C) infrared
  • (D) ultraviolet
Show Answer

Answer: C – All warm objects emit infrared radiation, and hotter objects emit more. Thermal-imaging (night-vision) cameras detect this infrared and convert it into a visible picture.

Q15. An endoscope lets a doctor see inside a patient’s body. Light is sent along a bundle of thin glass fibres and the reflected light returns along other fibres. Which radiation travels along the optical fibres?

  • (A) visible light
  • (B) gamma rays
  • (C) radio waves
  • (D) sound waves
Show Answer

Answer: A – Optical fibres carry visible light by total internal reflection, so they can be used in endoscopes for medical imaging and in photography/camera systems. Sound is not an electromagnetic wave at all.

Q16. A bank prints an invisible mark on a banknote that can only be seen when it glows (fluoresces) under a special lamp. Which radiation does the lamp emit?

  • (A) infrared
  • (B) microwaves
  • (C) gamma rays
  • (D) ultraviolet
Show Answer

Answer: D – Ultraviolet radiation makes some materials fluoresce, giving off visible light. This is used in security marking on banknotes and property, and in fluorescent tube coatings.

Q17. A doctor needs a picture of a patient’s broken bone, and an airport scanner checks the contents of luggage. Which radiation is used in both cases?

  • (A) microwaves
  • (B) X-rays
  • (C) infrared
  • (D) radio waves
Show Answer

Answer: B – X-rays pass through soft tissue and soft materials but are absorbed more by dense material such as bone and metal, so they are used for medical imaging and airport security scanning.

Q18. Hospital surgical instruments are sterilised by exposing them to a strongly penetrating radiation that kills bacteria without heating the instruments. Which radiation is used?

  • (A) infrared
  • (B) visible light
  • (C) gamma rays
  • (D) microwaves
Show Answer

Answer: C – Gamma rays are very penetrating and kill micro-organisms, so they are used to sterilise medical equipment. Gamma rays from a controlled source are also used in radiotherapy to kill cancer cells.

Q19. Television and radio programmes are broadcast across a whole country from tall transmitters. Which waves carry these broadcasts?

  • (A) gamma rays
  • (B) ultraviolet
  • (C) X-rays
  • (D) radio waves
Show Answer

Answer: D – Radio waves have long wavelengths, travel long distances and can diffract around hills and buildings, making them ideal for radio and television broadcasting.

Q20. Which pairing of a radiation with its use is correct?

  • (A) X-rays – television remote controls
  • (B) ultraviolet – sterilising drinking water
  • (C) infrared – medical bone scans
  • (D) gamma rays – satellite communication
Show Answer

Answer: B – Ultraviolet radiation kills bacteria, so it is used to sterilise water. Remote controls use infrared, bone scans use X-rays, and satellite communication uses microwaves.


Dangers & Safety

Q21. What is the main danger to the body from very intense microwave radiation?

  • (A) It heats body tissue internally
  • (B) It causes sunburn
  • (C) It knocks electrons off atoms (ionisation)
  • (D) It damages eyes by making the lens glow
Show Answer

Answer: A – Microwaves are absorbed by water in body tissue and heat it from the inside, which can damage or kill cells. This is why microwave ovens have a metal mesh in the door to keep the waves inside. Sunburn is caused by ultraviolet, and microwaves are not ionising.

Q22. A worker stands too close to a very hot furnace. The main harm caused by the radiation reaching his skin is burns. Which radiation causes this?

  • (A) radio waves
  • (B) ultraviolet
  • (C) infrared
  • (D) X-rays
Show Answer

Answer: C – Hot objects emit large amounts of infrared radiation, which is absorbed by the skin and felt as heat. Intense infrared can burn the skin and damage the eyes.

Q23. Spending too long in strong sunlight can cause sunburn and, over many years, skin cancer. Which part of sunlight is mainly responsible?

  • (A) infrared
  • (B) ultraviolet
  • (C) visible light
  • (D) microwaves
Show Answer

Answer: B – Ultraviolet radiation from the Sun causes sunburn and can damage skin cells, leading to skin cancer. It can also damage the eyes, which is why sunglasses with UV protection and sun cream are recommended.

Q24. X-rays and gamma rays are described as ionising radiation. Why does this make them dangerous to living tissue?

  • (A) They warm the tissue until it cooks
  • (B) They are reflected by the skin into the eyes
  • (C) They travel too fast for the body to react
  • (D) They can remove electrons from atoms, damaging or mutating cells
Show Answer

Answer: D – Ionising radiation knocks electrons off atoms and molecules in cells. This can damage DNA, mutate cells and cause cancer, which is why exposure to X-rays and gamma rays is carefully controlled.

Q25. [Supplement] Gamma rays are usually the most dangerous electromagnetic radiation when the source is outside the body. What is the main reason?

  • (A) They have the highest frequency, so each wave carries the most energy and they are the most penetrating and ionising
  • (B) They travel faster than all other electromagnetic waves
  • (C) They have the longest wavelength
  • (D) They are the only electromagnetic waves that are transverse
Show Answer

Answer: A – Gamma rays have the highest frequency and shortest wavelength in the spectrum, so they carry the most energy. They penetrate deep into the body and ionise cells along their path. All EM waves travel at the same speed in a vacuum and all are transverse.

Q26. A radiographer stands behind a special screen and wears a lead apron when taking X-ray photographs. What is the purpose of the lead?

  • (A) Lead reflects X-rays back to the patient
  • (B) Lead makes the radiographer invisible to the machine
  • (C) Lead absorbs X-rays, reducing the dose reaching the radiographer
  • (D) Lead stops the X-ray machine from overheating
Show Answer

Answer: C – Lead is very dense and absorbs X-rays strongly, so lead aprons and screens shield staff. Keeping exposure time short and only taking X-rays when needed also reduce the dose.

Q27. Workers who work near X-ray or gamma sources wear a badge containing a piece of photographic film. What does the badge detect?

  • (A) How warm the worker becomes during the day
  • (B) The colour of light in the room
  • (C) How much sound the worker has been exposed to
  • (D) How much ionising radiation the worker has received, because the radiation darkens (fogs) the film
Show Answer

Answer: D – X-rays and gamma rays darken photographic film, just as visible light does in a camera. The film badge is checked regularly so that the worker’s radiation dose can be monitored.

Q28. Which detector is suitable for detecting infrared radiation?

  • (A) A photographic film badge
  • (B) A thermocouple connected to a voltmeter
  • (C) A microphone
  • (D) An aerial connected to a radio receiver
Show Answer

Answer: B – A thermocouple (or a blackened thermometer bulb) absorbs infrared and warms up, producing a measurable voltage or temperature rise. Aerials detect radio waves, and a microphone detects sound, which is not part of the EM spectrum.

Q29. Which action does NOT reduce the risk to a worker using a gamma ray source in a factory?

  • (A) Standing closer to the source to finish the job more quickly
  • (B) Keeping the source in a lead-lined box when it is not in use
  • (C) Using long handling tongs to keep the source away from the body
  • (D) Spending as short a time as possible near the source
Show Answer

Answer: A – The three real safety rules for ionising radiation are shielding (lead-lined box), distance (tongs, standing further away) and time (shortest possible exposure). Standing closer increases the dose and is the opposite of safe practice.

Q30. Which of these radiations is not ionising, so it cannot damage DNA directly?

  • (A) gamma rays
  • (B) X-rays
  • (C) radio waves
  • (D) ultraviolet at the highest frequencies
Show Answer

Answer: C – Only ultraviolet (at high frequency), X-rays and gamma rays have enough energy to ionise atoms. Radio waves have very low frequency and energy, so they are non-ionising; their only heating effect at normal levels is negligible.

Keep practising: Find revision pages for every board on the Physics MCQs page, and keep the key equations beside you with the IGCSE Physics Formula Sheet.

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