IGCSE Physics Electromagnetic Spectrum Questions and Worked Solutions (3.3) | 0625

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IGCSE Physics 0625 · Topic 3.3

IGCSE Physics Electromagnetic Spectrum Questions and Worked Solutions

50 topic-wise practice questions on Electromagnetic Spectrum (Unit 3: Waves), written to the Cambridge IGCSE Physics 0625 syllabus for 2026–2028, each with a step-by-step worked solution.

50 questions27 Core13 Extended10 Challenge111 marksTextbook §3.3 · pp. 160–166
Questions tagged Core are for all candidates (Papers 1 & 3). Questions tagged Extended are Supplement content (Papers 2 & 4). Questions 41–50 are harder Challenge questions. Try each question first, then tap Show solution to check your working.

Topic guide: Electromagnetic Spectrum

The electromagnetic spectrum is a family of transverse waves that all travel at the same speed in a vacuum. Each region has typical uses and, at high exposure, harmful effects.

Key formulas

c = f λc = 3.0 × 10⁸ m/s in a vacuum (approx. the same in air)Extended

Prerequisite knowledge

  • Wave properties and v = fλ (3.1)
  • Standard form

Exam tips & common mistakes

  • Learn the order with a mnemonic
  • All EM waves have the SAME speed in a vacuum
  • Pair each harmful effect with the correct region

Key facts from the syllabus (3.3)

  • Order of increasing frequency: radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays (wavelength decreases)
  • Radio: radio and TV, astronomy, RFID. Microwaves: satellite TV, mobile phones, ovens. Infrared: grills, remote controls, intruder alarms, thermal imaging, optical fibres
  • Visible: vision, photography, illumination. Ultraviolet: security marking, detecting fake notes, sterilising water
  • X-rays: medical and security scanning. Gamma: sterilising food and equipment, detecting and treating cancer
  • Harmful effects: microwaves — internal heating; infrared — skin burns; UV — damage to surface cells and eyes, skin cancer; X-rays and gamma — mutation or damage to cells
  • Satellite communication is mainly by microwaves (low orbit and geostationary satellites)
  • Extended mobile phones and Wi-Fi use microwaves; Bluetooth uses radio waves; optical fibres use visible light or infrared
  • Extended digital signals have two levels; they can be regenerated accurately, giving higher data rates and greater range

Textbook: §3.3 Electromagnetic spectrum, pp. 160–166

1
Core[2 marks]

List the regions of the electromagnetic spectrum in order of increasing frequency.

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Method: Radio lowest, gamma highest.

Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays
2
Core[1 mark]

State the region of the electromagnetic spectrum with the longest wavelength.

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Method: Radio.

Radio waves
3
Core[1 mark]

State what all electromagnetic waves have in common regarding their speed in a vacuum.

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Method: Same speed.

They all travel at the same speed in a vacuum
4
Core[2 marks]

State one use of radio waves and one use of microwaves.

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Method: Syllabus uses.

Radio: radio/TV transmission, astronomy, RFID. Microwaves: satellite TV, mobile phones, microwave ovens
5
Core[2 marks]

State two uses of infrared radiation.

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Method: Syllabus uses.

Any two: electric grills, TV remote controls, intruder alarms, thermal imaging, optical fibres
6
Core[2 marks]

State two uses of ultraviolet radiation.

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Method: Syllabus uses.

Security marking, detecting fake bank notes, sterilising water
7
Core[1 mark]

State one use of X-rays.

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Method: Medical/security.

Medical scanning (or security scanners)
8
Core[2 marks]

State two uses of gamma rays.

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Method: Sterilising, cancer.

Sterilising food and medical equipment; detecting and treating cancer
9
Core[1 mark]

State one harmful effect of excessive exposure to microwaves.

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Method: Internal heating.

Internal heating of body cells
10
Core[1 mark]

State the harmful effect of excessive exposure to infrared.

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Method: Burns.

Skin burns
11
Core[2 marks]

State the harmful effects of excessive exposure to ultraviolet.

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Method: Surface cells and eyes.

Damage to surface cells and eyes, leading to skin cancer and eye conditions
12
Core[1 mark]

State the harmful effect of X-rays and gamma rays.

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Method: Ionising.

Mutation or damage to cells in the body
13
Core[1 mark]

State the region of the spectrum mainly used for communicating with artificial satellites.

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Method: Microwaves.

Microwaves
14
Core[1 mark]

State the region of the electromagnetic spectrum between visible light and X-rays.

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Method: UV.

Ultraviolet
15
Core[1 mark]

State the region of the electromagnetic spectrum between microwaves and visible light.

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Method: Infrared.

Infrared
16
Core[1 mark]

State which electromagnetic waves have the highest frequency.

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Method: Gamma.

Gamma rays
17
Core[2 marks]

State two properties shared by all electromagnetic waves.

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Method: Transverse, same speed.

They are transverse and travel at the same speed in a vacuum (and can travel through a vacuum)
18
Core[2 marks]

State which region of the spectrum is used in TV remote controls.

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Method: Infrared.

Infrared
19
Core[2 marks]

State which region of the spectrum is used for sterilising water.

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Method: UV.

Ultraviolet
20
Core[2 marks]

State which region of the spectrum is used for security scanners at airports.

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Method: X-rays.

X-rays
21
Core[2 marks]

State which region is used for RFID tags.

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Method: Radio.

Radio waves
22
Core[2 marks]

Explain why X-rays are used to image bones.

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Method: Absorbed by bone.

X-rays pass through soft tissue but are absorbed by bone
23
Core[2 marks]

State why ultraviolet is used to detect forged bank notes.

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Method: Fluorescence.

Genuine notes have marks that fluoresce (glow) under UV
24
Core[2 marks]

State one precaution against excessive ultraviolet exposure.

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Method: Sunscreen.

Use sunscreen/sunglasses or limit time in strong sunlight
25
Core[2 marks]

Explain why radiographers leave the room when taking an X-ray.

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Method: Reduce exposure.

Repeated exposure to X-rays can damage cells
26
Core[2 marks]

State the type of satellite used for direct broadcast satellite television.

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Method: Geostationary.

Geostationary satellites
27
Core[2 marks]

State the type of satellite used by some satellite phones.

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Method: Low orbit.

Low orbit satellites (some also use geostationary)
28
Extended[1 mark]

State the speed of electromagnetic waves in a vacuum.

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Method: Syllabus value.

3.0 × 10⁸ m/s
29
Extended[3 marks]

A radio station broadcasts at a frequency of 100 MHz. Calculate the wavelength.

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Method: λ = c ÷ f.

λ = 3.0×10⁸ ÷ 1.0×10⁸ = 3.00 m
30
Extended[3 marks]

Microwaves used in an oven have wavelength 0.12 m. Calculate their frequency.

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Method: f = c ÷ λ.

f = 3.0×10⁸ ÷ 0.12 = 2.5 × 10⁹ Hz
31
Extended[2 marks]

Explain why mobile phones use microwaves.

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Method: Penetrate some walls, short aerial.

Microwaves can penetrate some walls and only need a short aerial for transmission and reception
32
Extended[2 marks]

Explain why Bluetooth uses radio waves.

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Method: Pass through walls.

Radio waves pass through walls, although the signal is weakened
33
Extended[2 marks]

State the difference between an analogue signal and a digital signal.

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Method: Continuous vs two levels.

Analogue varies continuously; digital has only two values (on/off, 1/0)
34
Extended[3 marks]

Explain two benefits of digital signalling over analogue signalling.

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Method: Data rate, regeneration.

Higher rate of data transmission; signals can be regenerated accurately (noise removed), giving greater range
35
Extended[3 marks]

A mobile phone signal has frequency 1.8 GHz. Calculate its wavelength.

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Method: λ = c/f.

λ = 3.0×10⁸ ÷ 1.8×10⁹ = 0.167 m
36
Extended[3 marks]

X-rays have wavelength 1.0 × 10⁻¹⁰ m. Calculate their frequency.

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Method: f = c/λ.

f = 3.0 × 10¹⁸ Hz
37
Extended[2 marks]

Explain why optical fibres use visible light or infrared rather than radio waves.

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Method: Glass transparent, high data rate.

Glass is transparent to visible and short-wavelength infrared, and these can carry high rates of data
38
Extended[2 marks]

Explain why a digital signal can be regenerated accurately but an analogue signal cannot.

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Method: Two levels.

Digital has only two levels, so noise can be removed by restoring each pulse; analogue noise cannot be separated from the signal
39
Extended[2 marks]

Explain how sound is transmitted as a digital signal.

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Method: Sampled and coded.

The sound wave is sampled and each value is converted into a code of 1s and 0s that is transmitted
40
Extended[2 marks]

State the speed of electromagnetic waves in air approximately.

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Method: ≈ vacuum.

About 3.0 × 10⁸ m/s

Challenge questions

Harder, multi-step questions at the top end of the exam. Attempt these once you are confident with the questions above.

41
ChallengeCore[4 marks]

For each of microwaves, infrared and ultraviolet, state one use and one harmful effect of excessive exposure.

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Method: Syllabus lists.

Microwaves: mobile phones/ovens; internal heating of cells. Infrared: remote controls/thermal imaging; skin burns. UV: security marking/sterilising water; skin cancer and eye damage
42
ChallengeCore[4 marks]

Explain why X-rays are used for medical imaging and why radiographers stand behind lead screens.

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Method: Penetration and ionisation.

X-rays pass through soft tissue but are absorbed by bone, producing images; they are ionising and repeated exposure damages cells, so staff are shielded
43
ChallengeCore[3 marks]

Explain why gamma rays can sterilise food in sealed packets.

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Method: Penetrating, kills bacteria.

They penetrate the packaging and kill bacteria without opening the packet
44
ChallengeCore[3 marks]

Explain why satellite TV uses microwaves and why some satellite phones use low-orbit satellites.

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Method: Pass through atmosphere.

Microwaves pass through the atmosphere easily; low-orbit satellites are closer, so signals are stronger with smaller phone aerials
45
ChallengeExtended[4 marks]

A radio station broadcasts on 909 kHz and a Wi-Fi router on 2.4 GHz. Calculate both wavelengths.

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Method: λ = c/f.

330 m and 0.125 m
46
ChallengeExtended[4 marks]

A signal is sent by microwaves to a geostationary satellite 3.6 × 10⁷ m above the Earth and back down. Calculate the minimum delay.

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Method: Round trip.

t = 7.2×10⁷ ÷ 3.0×10⁸ = 0.240 s
47
ChallengeExtended[4 marks]

Explain why digital signals can travel further than analogue signals without loss of quality.

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Method: Regeneration.

Noise added along the way can be removed by regenerating the 1s and 0s at repeaters; analogue noise is amplified with the signal
48
ChallengeExtended[4 marks]

Explain why optical fibres carrying infrared allow much higher data rates than copper cables or radio waves.

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Method: High frequency.

Light/short-wave infrared has very high frequency so can carry far more pulses per second; glass is transparent to these wavelengths
49
ChallengeExtended[3 marks]

Explain why Bluetooth uses radio waves while mobile phones use microwaves.

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Method: Walls.

Radio waves pass through walls (weakened) for short-range links; microwaves penetrate some walls and need only short aerials for phone communication
50
ChallengeExtended[4 marks]

Explain the process of sending a sound as a digital signal and one advantage over an analogue signal.

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Method: Sampling.

The sound is sampled many times a second, each value converted to binary and sent as pulses; noise can be removed so the signal is regenerated accurately
All IGCSE Physics topics← 3.2.4 Dispersion of Light3.4 Sound →

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