Electromagnetic spectrum
Cambridge IGCSE Physics (0625) · Unit 3: Waves · 20 flashcards
Electromagnetic spectrum is topic 3.3 in the Cambridge IGCSE Physics (0625) syllabus , positioned in Unit 3 — Waves , alongside General properties of waves, Reflection of light and Refraction of light. In one line: Radio waves, Microwaves, Infrared radiation, Visible light, Ultraviolet radiation, X-rays, Gamma rays. This is the order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency).
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across undefined questions worth 153 marks (around 2.4% of all Physics marks in those years).
The deck below contains 20 flashcards — 5 definitions — covering the precise wording mark schemes reward. Use the 5 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
State the main regions of the electromagnetic spectrum in order of decreasing wavelength
Radio waves, Microwaves, Infrared radiation, Visible light, Ultraviolet radiation, X-rays, Gamma rays. This is the order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency).
What the Cambridge 0625 syllabus says
2026-2028 syllabus, in our wordsWhat the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).
- Know Know the order of the main electromagnetic spectrum regions, both by frequency and by wavelength.
- Know Know that every type of electromagnetic wave travels at the same, very high speed in a vacuum.
- Describe Describe what each part of the electromagnetic spectrum is typically used for, including: (a) radio waves: radio and TV broadcasting, radio astronomy, RFID (radio frequency identification) tags; (b) microwaves: mobile (cell) phones, microwave ovens and satellite TV; (c) infrared: thermal imaging, intruder alarms, electric grills, optical fibres, and short-range links such as TV remote controls; (d) visible light: seeing, photography and lighting; (e) ultraviolet: sterilising water, security marking and checking bank notes for forgeries; (f) X-rays: security scanners and medical scanning; (g) gamma rays: detecting and treating cancer, and sterilising medical equipment and food.
- Describe Describe the ways people can be harmed by too much electromagnetic radiation, including: (a) microwaves heat body cells from the inside; (b) infrared burns the skin; (c) ultraviolet damages the eyes and surface cells, which can cause eye conditions and skin cancer; (d) X-rays and gamma rays can damage cells in the body or cause mutations.
- Know Know that electromagnetic waves travel at 3.0 × 10⁸ m/s in a vacuum and at roughly the same speed in air. Supplement
- Know Know that microwaves are mostly used to communicate with artificial satellites: (a) low-orbit satellites are used by some satellite phones; (b) geostationary satellites are used by direct broadcast satellite TV and by some satellite phones.
- Know Know that many key communication systems depend on electromagnetic radiation, including: (a) microwaves for wireless internet and mobile (cell) phones, since microwaves get through some walls and a short aerial is enough to send and receive them; (b) radio waves for Bluetooth, since radio waves can get through walls, though the signal is weakened as they do; (c) optical fibres for high-speed broadband and cable TV, using visible light or infrared: glass is transparent to some infrared as well as to visible light, and visible light and infrared of short wavelength can carry data at high rates. Supplement
- Know Know how a digital signal differs from an analogue signal. Supplement
- Know Know that sound can be sent as either a digital signal or an analogue signal. Supplement
- Explain Explain the advantages of digital signals, including faster data transmission and greater range because the signal can be regenerated accurately. Supplement
State the main regions of the electromagnetic spectrum in order of decreasing wavelength.
Radio waves, Microwaves, Infrared radiation, Visible light, Ultraviolet radiation, X-rays, Gamma rays. This is the order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency).
State the main regions of the electromagnetic spectrum in order of increasing frequency.
Radio waves, Microwaves, Infrared radiation, Visible light, Ultraviolet radiation, X-rays, Gamma rays. Increasing frequency means decreasing wavelength.
State the speed of all electromagnetic waves when travelling in a vacuum. Include the unit.
The speed of all electromagnetic waves in a vacuum is 3.0 x 10^8 m/s. This is also known as the speed of light and is constant for all EM waves in a vacuum.
Microwaves and radio waves are both part of the electromagnetic spectrum. Radio waves have a longer wavelength than microwaves. Which of these waves will travel faster in a vacuum? Explain your answer.
Neither. All electromagnetic waves travel at the same speed in a vacuum (3.0 x 10^8 m/s), regardless of their wavelength or frequency. Therefore, radio waves and microwaves will travel at the same speed.
State one use of each of the following regions of the electromagnetic spectrum: (a) Microwaves (b) Gamma rays
(a) Microwaves: Mobile phone communication (or Satellite television, or Microwave ovens)
(b) Gamma rays: Sterilising food (or Sterilising medical equipment, or Detection of cancer, or Treatment of cancer)
Each correct use gets 1 mark.
Describe how infrared radiation is used in a remote controller for a television.
The remote controller emits a beam of infrared radiation.
Different buttons on the remote produce a unique pattern or code of infrared pulses.
The television receiver detects the infrared signal and interprets the code to perform the corresponding function (
Describe one harmful effect on people of excessive exposure to microwaves.
Excessive exposure to microwaves can cause internal heating of body cells. This is because microwaves are absorbed by water molecules in the body, causing them to vibrate and generate heat.
State one harmful effect of excessive exposure to ultraviolet (UV) radiation.
Excessive exposure to UV radiation can cause skin cancer or damage to the eyes, leading to eye conditions such as cataracts.
Calculate the distance, in meters, that an electromagnetic wave travels in air in 5.0 seconds. State your answer in standard form.
Distance = Speed x Time
Speed of electromagnetic wave in air ≈ 3.0 x 10⁸ m/s
Time = 5.0 s
Distance = (3.0 x 10⁸ m/s) x (5.0 s) = 1.5 x 10⁹ m
The distance is calculated by multiplying the speed of light in air by the time it travels for.
State the approximate speed of electromagnetic waves in air.
The approximate speed of electromagnetic waves in air is 3.0 x 10⁸ m/s.
Electromagnetic waves, such as light and radio waves, travel at a very high speed in air, close to their speed in a vacuum.
State the region of the electromagnetic spectrum mainly used for communication with artificial satellites.
Microwaves.
Microwaves are used due to their ability to penetrate the Earth's atmosphere and travel long distances with minimal interference, making them suitable for satellite communication.
Describe two key differences between low orbit artificial satellites and geostationary satellites, focusing on their application in satellite communication.
1. Orbital Height & Coverage: Low orbit satellites are much closer to the Earth, providing limited geographic coverage at any one time, whereas geostationary satellites maintain a fixed position relative to Earth, offering continuous coverage over a large area.
2. Latency: Low orbit satellites exhibit lower latency due to their proximity to Earth, making them better for real-time communication. Geostationary satellites have higher latency due to the longer signal path, which may cause a slight delay. Note: Latency is the delay before a transfer of data begins following an instruction for its transfer.
State two reasons why microwaves are used for mobile phone communication.
1. Microwaves can penetrate some walls.
2. Microwaves only require a short aerial for transmission and reception.
(Each correct reason is worth 1 mark.)
Explain why optical fibres are used for cable television and high-speed broadband.
Optical fibres are made of glass, which is transparent to visible light and some infrared radiation. Visible light and short wavelength infrared can carry high rates of data, allowing for faster communication and a greater bandwidth than other types of waves (such as radio waves or microwaves).
State two differences between a digital signal and an analogue signal.
1. Amplitude/Voltage/Value: Analogue signals can take any continuous value within a range, while digital signals have discrete, specific values (often just 0 and 1).
2. Noise: Analogue signals are more susceptible to noise and interference, which can distort the signal. Digital signals are more robust against noise, as small changes don't affect the discrete values.
A microphone converts sound waves into an electrical signal. Describe how the electrical signal would differ if it were processed as an analogue signal compared to a digital signal.
With an analogue signal, the voltage would vary continuously to match the sound wave's amplitude. The voltage can take any value within the range of the circuit. With a digital signal, the continuous voltage variation is sampled at regular intervals. Each sample is then converted into a binary number (0 or 1 represented by a voltage level). Therefore, the digital signal is a series of discrete binary numbers representing the amplitude of the sound wave at specific times.
State two differences between analogue and digital signals used to transmit sound.
1. Analogue signals are continuous, while digital signals are discrete (made of 1s and 0s).
2. Analogue signals are more susceptible to noise/interference than digital signals.
Describe one advantage of using digital signals, rather than analogue signals, to transmit sound over long distances. Explain why this is an advantage.
Digital signals can be regenerated/reconstructed. This means that any noise/interference picked up during transmission can be removed, resulting in a clearer sound at the receiving end compared to analogue signals, where noise is amplified along with the original signal. Therefore, digital signals can travel for long distances with minimal signal degradation.
Explain how digital signalling allows for increased range compared to analogue signalling.
Digital signals can be accurately regenerated at repeater stations along the transmission path. Analogue signals degrade with distance due to noise and attenuation, and any noise is amplified along with the signal by repeaters. Digital signals, being discrete (
State two benefits of using digital signalling over analogue signalling.
1. Increased rate of data transmission: Digital signals can encode more information per unit time. 2. Increased range: Digital signals can be regenerated accurately, reducing signal degradation over long distances.
Key Questions: Electromagnetic spectrum
State the main regions of the electromagnetic spectrum in order of decreasing wavelength.
Radio waves, Microwaves, Infrared radiation, Visible light, Ultraviolet radiation, X-rays, Gamma rays. This is the order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency).
State the speed of all electromagnetic waves when travelling in a vacuum. Include the unit.
The speed of all electromagnetic waves in a vacuum is 3.0 x 10^8 m/s. This is also known as the speed of light and is constant for all EM waves in a vacuum.
State one use of each of the following regions of the electromagnetic spectrum: (a) Microwaves (b) Gamma rays
(a) Microwaves: Mobile phone communication (or Satellite television, or Microwave ovens)
(b) Gamma rays: Sterilising food (or Sterilising medical equipment, or Detection of cancer, or Treatment of cancer)
Each correct use gets 1 mark.
State the region of the electromagnetic spectrum mainly used for communication with artificial satellites.
Microwaves.
Microwaves are used due to their ability to penetrate the Earth's atmosphere and travel long distances with minimal interference, making them suitable for satellite communication.
State two differences between a digital signal and an analogue signal.
1. Amplitude/Voltage/Value: Analogue signals can take any continuous value within a range, while digital signals have discrete, specific values (often just 0 and 1).
2. Noise: Analogue signals are more susceptible to noise and interference, which can distort the signal. Digital signals are more robust against noise, as small changes don't affect the discrete values.
Tips to avoid common mistakes in Electromagnetic spectrum
- ● To solve electromagnetism questions, first find the coil's poles (N/S) using the right-hand grip rule, then remember: like poles repel, unlike poles attract.
- ● To determine coil polarity (N or S), use the right-hand grip rule; the left-hand rule is exclusively for electric motors.
- ● Learn the difference between slip rings (AC generators) and commutators (DC motors) — they're not interchangeable.
- ● Memorize the volt's alternative unit (J/C) by remembering the link between energy, charge, and potential difference: Voltage = Energy / Charge.
- ● Remember that charged items can induce a temporary charge in neutral objects, leading to electrostatic attraction.
More topics in Unit 3 — Waves
Electromagnetic spectrum sits alongside these Physics decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0625 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Electromagnetic spectrum deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
Related Physics guides
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