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
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- Know Know the main regions of the electromagnetic spectrum in order of frequency and in order of wavelength
- Know Know that all electromagnetic waves travel at the same high speed in a vacuum
- Describe Describe typical uses of the different regions of the electromagnetic spectrum including: (a) radio waves; radio and television transmissions, astronomy, radio frequency identification (RFID) (b) microwaves; satellite television, mobile phones (cell phones), microwave ovens (c) infrared; electric grills, short range communications such as remote controllers for televisions, intruder alarms, thermal imaging, optical fibres (d) visible light; vision, photography, illumination (e) ultraviolet; security marking, detecting fake bank notes, sterilising water (f) X-rays; medical scanning, security scanners (g) gamma rays; sterilising food and medical equipment, detection of cancer and its treatment
- Describe Describe the harmful effects on people of excessive exposure to electromagnetic radiation, including: (a) microwaves; internal heating of body cells (b) infrared; skin burns (c) ultraviolet; damage to surface cells and eyes, leading to skin cancer and eye conditions (d) X-rays and gamma rays; mutation or damage to cells in the body
- Know Know that the speed of electromagnetic waves in a vacuum is 3.0 x 108m/s and is approximately the same in air Supplement
- Know Know that communication with artificial satellites is mainly by microwaves: (a) some satellite phones use low orbit artificial satellites (b) some satellite phones and direct broadcast satellite television use geostationary satellites
- Know Know that many important systems of communications rely on electromagnetic radiation including: (a) mobile phones (cell phones) and wireless internet use microwaves because microwaves can penetrate some walls and only require a short aerial for transmission and reception (b) Bluetooth uses radio waves because radio waves pass through walls but the signal is weakened on doing so (c) optical fibres (visible light or infrared) are used for cable television and high-speed broadband because glass is transparent to visible light and some infrared; visible light and short wavelength infrared can carry high rates of data Supplement
- Know Know the difference between a digital and analogue signal Supplement
- Know Know that a sound can be transmitted as a digital or analogue signal Supplement
- Explain Explain the benefits of digital signalling including increased rate of transmission of data and increased range due to accurate signal regeneration 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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