What is the electromagnetic spectrum in the context of Cambridge IGCSE Physics?

The electromagnetic spectrum is a range of all types of electromagnetic radiation. In Cambridge IGCSE Physics, it includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Each type of radiation has different wavelengths and frequencies, and they all travel at the speed of light in a vacuum.

How are the different types of waves in the electromagnetic spectrum used in everyday life?

Different types of electromagnetic waves have various applications in everyday life. Radio waves are used for broadcasting and communication, microwaves for cooking and satellite transmissions, infrared for remote controls and thermal imaging, visible light for seeing, ultraviolet for sterilization, X-rays for medical imaging, and gamma rays for cancer treatment.

Why is understanding the electromagnetic spectrum important in Physics?

Understanding the electromagnetic spectrum is crucial in Physics because it helps explain how different types of electromagnetic waves interact with matter. This knowledge is essential for developing technologies such as medical imaging, communication systems, and various scientific instruments. It also helps in understanding natural phenomena like the greenhouse effect and the behavior of light.

What are the key differences between the types of electromagnetic waves?

The key differences between the types of electromagnetic waves are their wavelengths and frequencies. Radio waves have the longest wavelengths and lowest frequencies, while gamma rays have the shortest wavelengths and highest frequencies. These differences affect how each type of wave interacts with matter and their practical applications.

How does the speed of electromagnetic waves compare across the spectrum?

All electromagnetic waves travel at the same speed in a vacuum, which is the speed of light, approximately 3 x 10^8 meters per second. This constant speed is a fundamental property of electromagnetic waves, regardless of their frequency or wavelength, and is a key concept in the study of waves in Cambridge IGCSE Physics.

Why is "Saying X-rays travel faster than radio waves" a common mistake in Electromagnetic Spectrum?

Why it happens: Confusing 'energy' with 'speed'. How to avoid it: All EM waves travel at the SAME speed in a vacuum: c = 3.0 × 10^8\,m/s. Source: 0625/42 — recurring

Why is "Putting microwaves above visible light" a common mistake in Electromagnetic Spectrum?

Why it happens: Random ordering. How to avoid it: Memorise: radio < microwave < IR < visible < UV < X-ray < gamma (increasing frequency).

Why is "Saying highest frequency has the longest wavelength" a common mistake in Electromagnetic Spectrum?

Why it happens: Inverting c = f. How to avoid it: Speed is constant → high f ↔ low (inversely proportional).

Why is "Listing 'cooking food' as a use of UV" a common mistake in Electromagnetic Spectrum?

Why it happens: Mixing IR / microwave with UV. How to avoid it: Cooking → IR (grills) or microwaves (microwave ovens). UV → suntanning beds, sterilisation, fluorescence.

Cambridge IGCSE Physics (0625)

Electromagnetic Spectrum

Q: Why is "Saying highest frequency has the longest wavelength" a common mistake in Electromagnetic Spectrum?

Why it happens: Inverting c = f. How to avoid it: Speed is constant → high f ↔ low (inversely proportional).

Q: Why is "Listing 'cooking food' as a use of UV" a common mistake in Electromagnetic Spectrum?

Why it happens: Mixing IR / microwave with UV. How to avoid it: Cooking → IR (grills) or microwaves (microwave ovens). UV → suntanning beds, sterilisation, fluorescence.

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Short Notes - Electromagnetic Spectrum

Detailed Study Notes

Detailed notes on Waves for Cambridge IGCSE Physics, covering key concepts, explanations, examples, and exam-focused revision points.

Electromagnetic Spectrum — Cambridge IGCSE 0625 Physics Extended (2026)

All EM waves travel at $3 \times 10^{8}\,\text{m/s}$ in vacuum. Memorise the seven bands in order, plus a use and a danger for each.

At a glance

Order (long $\lambda$ → short $\lambda$ ): Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma.
Mnemonic: Radio Moves In Verbs Until X-mas Gifts.
All EM waves: transverse, $3 \times 10^{8}\,\text{m/s}$ in vacuum, no medium needed.
Higher frequency / shorter wavelength → MORE energy → more dangerous.
Each band has a use AND a hazard.
Satellite communication uses microwaves: low-orbit (some satellite phones) and geostationary (satellite TV).
Analogue = continuous; digital = two values (1/0). Digital can be regenerated → greater range and higher data rate.

What you’ll learn

Mapped to the Cambridge IGCSE 0625 syllabus (2026-2028).

3.3 — Describe the EM spectrum and the order of its bands.
3.3 — State that all EM waves travel at the same speed in vacuum.
3.3 — Recall typical uses and hazards of each band.
3.3 — Know that satellite communication uses microwaves (low-orbit and geostationary satellites).
3.3 — Know the difference between digital and analogue signals and explain the benefits of digital signalling.

Order of the spectrum

Long wavelength (low frequency, low energy) on the left; short wavelength on the right.

Order, longest wavelength to shortest:

Band	Use	Hazard
Radio waves	TV, radio broadcasts	Generally safe
Microwaves	Cooking, satellite communication, mobile phones	Internal heating of body tissue
Infrared	Heaters, remote controls, thermal imaging	Burns to skin
Visible light	Vision, photography, optical fibre comms	High brightness damages retina
Ultraviolet	Sterilising, fluorescence, security marking	Skin cancer, sunburn, eye damage
X-rays	Medical imaging (broken bones), security scanners	Cell damage, mutation, cancer
Gamma rays	Cancer treatment (radiotherapy), sterilising medical instruments	Cell damage, mutation, cancer

Memorise the order: Radio, Microwave, Infrared, Visible, Ultraviolet, X-rays, Gamma.

Seven bands, longest wavelength on the left; frequency and energy rise towards gamma rays.

As you go right (towards gamma):

Wavelength DECREASES.
Frequency INCREASES.
Energy per photon INCREASES.
Hazard generally INCREASES.

7 bands, longest $\lambda$ to shortest.
Frequency rises left to right.
Use the mnemonic to remember order.
Hazard scales with frequency.

Shared properties of all EM waves

Transverse, $3 \times 10^{8}\,\text{m/s}$ in vacuum, can travel through vacuum.

All EM waves share:

They are TRANSVERSE.
Travel at $3 \times 10^{8}\,\text{m/s}$ in vacuum (denoted $c$ ).
Need no medium — propagate through space.
Obey $v = f\lambda$ .
Can be reflected, refracted, diffracted.

Worked. Yellow light has wavelength $580\,\text{nm} = 580 \times 10^{-9}\,\text{m}$ . Find frequency.

$f = c/\lambda = (3 \times 10^{8})/(580 \times 10^{-9}) \approx 5.17 \times 10^{14}\,\text{Hz}$ .

Differences across bands. Only wavelength and frequency differ. Same speed in vacuum.

In other media. EM waves slow down: in glass, light travels at $c/1.5 \approx 2 \times 10^{8}\,\text{m/s}$ . The frequency stays the same; wavelength shrinks.

All EM waves are transverse: wavelength is peak-to-peak; amplitude is the height from the rest line.

Transverse, $c = 3 \times 10^{8}\,\text{m/s}$ in vacuum.
All bands obey $v = f\lambda$ .
Only $\lambda$ and $f$ change between bands.
Slower (and shorter $\lambda$ ) in denser media.

Uses and hazards — examples to memorise

Cambridge wants ONE use and ONE hazard for each named band.

Radio.

Use: terrestrial TV, FM/AM radio broadcasts.
Hazard: very low.

Microwaves.

Use: microwave ovens (resonates with water molecules), Wi-Fi, satellite TV, mobile phone signals.
Hazard: deep tissue heating; long-term exposure concerns near transmitters.

Infrared.

Use: TV remote controls, thermal imaging cameras (used by emergency services), heaters, optical fibres for short distances.
Hazard: skin burns from intense IR (e.g. heat lamps).

Visible.

Use: photography, vision, optical communications.
Hazard: bright light (especially lasers) damages the retina.

Ultraviolet.

Use: detecting fake banknotes, sterilising water/medical instruments, suntanning beds.
Hazard: sunburn, premature skin ageing, skin cancer, cataracts.

X-rays.

Use: medical imaging of bones; airport security scanners.
Hazard: ionises atoms in cells → cell damage / cancer with prolonged exposure. Hospital staff wear lead aprons.

Gamma.

Use: cancer treatment (radiotherapy), sterilising surgical instruments, food irradiation, detecting tumours.
Hazard: deeply penetrating; severe cell damage / cancer / death at high doses.

Tip. Cambridge mark schemes accept any reasonable use/hazard from the list — pick ones you can spell.

Each band: one use + one hazard.
Microwaves cook by exciting water.
UV: ozone layer blocks most.
Gamma: radiotherapy is a beneficial use.

Satellite communication

Communication with satellites is mainly by microwaves — low-orbit and geostationary.

Communication with artificial satellites is mainly by microwaves. Microwaves are used because they can pass through the atmosphere (including clouds) and only require a short aerial for transmission and reception.

Two kinds of satellite are used:

Low-orbit (low Earth orbit) satellites — orbit close to the Earth and move quickly across the sky. Some satellite phones use low-orbit satellites.
Geostationary satellites — orbit much higher and stay above a fixed point on the Earth's equator (their orbit takes 24 hours, matching the Earth's rotation). Some satellite phones and direct broadcast satellite television use geostationary satellites — because the satellite appears stationary, a home dish can point at a fixed spot in the sky.

Microwaves pass easily through the atmosphere; low-orbit satellites sit close and move fast, while geostationary satellites stay fixed above the equator for TV dishes.

Satellite communication is mainly by microwaves.
Microwaves pass through the atmosphere and need only a short aerial.
Low-orbit satellites: some satellite phones.
Geostationary satellites: satellite TV and some satellite phones.

Digital and analogue signals

Analogue = continuous; digital = two values. Digital can be regenerated.

Information (such as sound) can be transmitted as either an analogue or a digital signal.

An analogue signal varies continuously — it can take any value, smoothly following the quantity it represents (e.g. the changing pressure of a sound wave).
A digital signal has only two values — usually called high and low, or 1 and 0. It changes in steps and is not continuous.

A sound can be transmitted as either a digital or an analogue signal.

An analogue signal can take any value; a digital signal steps between just two levels, so it can be regenerated free of noise.

Why digital is better — signal regeneration. As any signal travels along a cable or through the air it is weakened and picks up unwanted noise. A digital signal only has to be recognised as 'high' or 'low', so even after noise has been added it can be regenerated — cleaned and rebuilt into a perfect string of 1s and 0s. An analogue signal cannot be cleaned in this way, because the noise becomes part of the continuously varying signal.

Benefits of digital signalling:

Increased rate of transmission of data — more information can be sent per second.
Increased range — because the signal can be accurately regenerated by repeaters along the route, it can be sent over much greater distances without loss of quality.

Analogue: continuous, any value.
Digital: two values (1/0), changes in steps.
Digital can be regenerated to remove noise.
Benefits: higher data rate and greater range.

Quick recap

Order: Radio, Microwave, IR, Visible, UV, X-ray, Gamma.
All EM waves: transverse, $c = 3 \times 10^{8}\,\text{m/s}$ in vacuum.
Frequency rises, wavelength falls, energy rises, hazard rises (left to right).
Memorise one use AND one hazard per band.
Satellites: microwaves; low-orbit (sat phones) and geostationary (sat TV).
Digital = two values; can be regenerated → greater range + higher data rate.

Memorise this

Verbatim phrases and definitions Cambridge mark schemes credit.

Electromagnetic spectrum — family of transverse waves all travelling at $c$ in vacuum.
Speed of light in vacuum — $c = 3 \times 10^{8}\,\text{m/s}$ .
Ionising radiation — radiation with enough energy to ionise atoms (UV and above).
Analogue signal — varies continuously, can take any value.
Digital signal — only two values (1/0), changes in steps, can be regenerated.
Benefits of digital signalling — increased rate of transmission of data and increased range, due to accurate signal regeneration.

How it’s examined

EM spectrum appears every Paper 2 (3-4 marks: order, use, hazard) and most Paper 4s (4-5 marks: $v = f\lambda$ for a specific band, properties of EM waves). Examiner reports flag wrong order (especially swapping IR/visible/UV) and giving 'TV' as a use of microwaves (it's radio for terrestrial; microwave for satellite).

Sources: Cambridge IGCSE Physics 0625 syllabus 2026-2028 (3.6); 0625/22 May/Jun 2024 — Q11 (EM spectrum order); 0625 Examiner Reports 2022-2024. Last reviewed 2026-05-06.

Take this whole topic with you

Step-by-step worked examples — Electromagnetic Spectrum

Step-by-step solutions to past-paper-style questions on electromagnetic spectrum, written exactly the way a tutor would explain them at the board.

Question type:

Question patterns to master — Electromagnetic Spectrum

Almost every electromagnetic spectrum exam question is one of these shapes. Learn to spot each one and you will always know how to start.

Identify & classify

Recognise it by

List in order, state a use, place this wavelength or rank instructions — the question tests which region a wave belongs to and what it does.

How to approach it

Recall the fixed order radio → microwave → IR → visible → UV → X-ray → gamma, then attach the standard use or hazard for each region; convert any wavelength to metres first to locate it.

Common trap

Examiner reports flag candidates confusing $\mu\text{m}$ ( $10^{-6}\,\text{m}$ ) with $\text{nm}$ ( $10^{-9}\,\text{m}$ ), or listing 'cooking' as a use of UV — cooking is IR or microwaves.

Direct calculation

Recognise it by

A single find or calculate instruction using $c = f\lambda$ with $c = 3.0 \times 10^{8}\,\text{m/s}$ .

How to approach it

Rearrange the wave equation for the unknown, substitute in SI units, and combine the powers of ten carefully.

Common trap

Examiner reports flag candidates assuming X-rays travel faster than radio waves — all EM waves share the same speed $c$ in a vacuum; only frequency and wavelength change.

Show that / prove

Recognise it by

Explain why — for example why gamma radiation is more dangerous than ultraviolet.

How to approach it

Link frequency to photon energy: higher frequency means higher energy per photon, which then causes more ionisation and DNA damage.

Common trap

Examiner reports flag candidates explaining hazard by 'speed' or 'intensity' — the danger comes from the energy per PHOTON, set by the frequency.

Graph or diagram

Recognise it by

A plotted graph — for example intensity against $1/d^{2}$ — where you must read a gradient and interpret the relationship.

How to approach it

Read the AXIS LABELS first, then use a straight line through the origin to confirm proportionality and take the gradient from widely separated points.

Common trap

Examiner reports flag candidates reading 'straight line through origin' as $I \propto d$ when the axis is actually $1/d^{2}$ — always check what each axis plots.

1Order the EM spectrum
CoreIdentify & classify• spectrum order
Question
List the seven regions of the EM spectrum in order of INCREASING frequency.
Step-by-step solution
1. Step 1
  Mnemonic: 'Roman Men Invented Very Unusual X-ray Guns'.
Answer
Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma.
2Match an EM region to its use
CoreIdentify & classify• Adapted from 0625/22 May/Jun 2024 Q14• uses
Question
State a use of microwaves and a use of X-rays.
Step-by-step solution
1. Step 1
  Microwaves: cooking; satellite/mobile phone communication.
2. Step 2
  X-rays: medical imaging of bones; airport security.
Answer
Microwaves: communications/cooking. X-rays: medical imaging.
3Speed of EM waves
ExtendedDirect calculation• c
Question
All EM waves travel at the same speed in a vacuum. State this speed and use it to find the wavelength of a $5 \times 10^{14}\,\text{Hz}$ wave.
Step-by-step solution
1. Step 1
  Speed.
  $c = 3.0 \times 10^{8}\,\text{m/s}$
2. Step 2
  Wave equation.
  $\lambda = \dfrac{c}{f} = \dfrac{3.0 \times 10^{8}}{5 \times 10^{14}} = 6.0 \times 10^{-7}\,\text{m}$
Answer
$\lambda = 600\,\text{nm}$ (visible light, orange-red).
4Biological effect of UV vs gamma
ExtendedShow that / prove• hazards
Question
Explain why gamma radiation is more dangerous than ultraviolet.
Step-by-step solution
1. Step 1
  Gamma has a much higher frequency → higher energy per photon.
2. Step 2
  Higher-energy photons cause more DNA damage and ionise more atoms in the body.
Answer
Gamma photons carry more energy → greater ionisation/DNA damage.
5Match each EM region to a common use
ExtendedIdentify & classify• Adapted from 0625/42 May/Jun 2023 Q15• uses
Question
State one use for each of: radio, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Step-by-step solution
1. Step 1
  Radio: broadcasting (TV/radio); mobile and satellite communication.
2. Step 2
  Microwaves: cooking in microwave ovens; mobile-phone and satellite communication.
3. Step 3
  Infrared: thermal imaging cameras; TV remote controls; short-range data links; cooking (grills).
4. Step 4
  Visible light: human vision; optical fibres for telecommunications; photography.
5. Step 5
  Ultraviolet: sterilising water; security marking (fluorescent dyes); detection of forgeries.
6. Step 6
  X-rays: medical imaging of bones; airport security scanners.
7. Step 7
  Gamma: sterilising medical instruments; treating cancer (radiotherapy); medical tracers.
Answer
Radio → broadcasting; microwaves → cooking/comms; IR → thermal imaging; visible → vision; UV → sterilisation; X-rays → bone imaging; gamma → cancer treatment.
6Identify a region from a wavelength
ExtendedIdentify & classify• spectrum order
Question
Place each wavelength in the correct EM region: (a) $1\,\text{m}$ , (b) $1\,\text{cm}$ , (c) $10\,\mu\text{m}$ , (d) $500\,\text{nm}$ , (e) $0.1\,\text{nm}$ .
Step-by-step solution
1. Step 1
  (a) $1\,\text{m}$ → radio (or short-wave radio).
2. Step 2
  (b) $1\,\text{cm} = 10^{-2}\,\text{m}$ → microwaves.
3. Step 3
  (c) $10\,\mu\text{m} = 10^{-5}\,\text{m}$ → infrared.
4. Step 4
  (d) $500\,\text{nm} = 5 \times 10^{-7}\,\text{m}$ → visible (green).
5. Step 5
  (e) $0.1\,\text{nm} = 10^{-10}\,\text{m}$ → X-rays.
Answer
(a) radio, (b) microwaves, (c) IR, (d) visible green, (e) X-rays.
Examiner tip
The examiner report flags candidates often confuse $\mu\text{m}$ ( $10^{-6}$ ) and $\text{nm}$ ( $10^{-9}$ ). Convert everything to metres before locating on the spectrum.
7Dangers of high-frequency EM
ExtendedIdentify & classify• hazards
Question
State one specific danger associated with each of: microwaves, UV, X-rays.
Step-by-step solution
1. Step 1
  Microwaves: internal heating of body tissue (water molecules) — can damage cells/eyes with prolonged exposure.
2. Step 2
  UV: damage to skin (sunburn, skin cancer) and to eyes (cataracts) due to photons energetic enough to break some chemical bonds.
3. Step 3
  X-rays: ionising radiation that can damage DNA in cells, increasing cancer risk over time.
Answer
Microwaves → tissue heating. UV → skin/eye damage. X-rays → ionisation/DNA damage.
8EM wave in vacuum — frequency calculation
ExtendedDirect calculation• c, v=fλ
Question
An X-ray has wavelength $1.5 \times 10^{-11}\,\text{m}$ . Using $c = 3.0 \times 10^{8}\,\text{m/s}$ , find its frequency.
Step-by-step solution
1. Step 1
  $c = f\lambda \Rightarrow f = c/\lambda$ .
  $f = \dfrac{3.0 \times 10^{8}}{1.5 \times 10^{-11}}$
2. Step 2
  Compute.
  $f = 2.0 \times 10^{19}\,\text{Hz}$
Answer
$f = 2.0 \times 10^{19}\,\text{Hz}$
9Digital versus analogue signals
Extended• digital, analogue, signals
Question
(a) State the difference between a digital signal and an analogue signal. (b) A sound is to be sent as an electrical signal down a long cable. Explain why the signal arrives more accurately if it is sent in digital form.
Step-by-step solution
1. Step 1
  (a) An analogue signal varies continuously and can take any value. A digital signal has only two values (high/low, often written 1 and 0) and changes in steps — it is not continuous.
2. Step 2
  Any signal picks up unwanted noise and is weakened (attenuated) as it travels along the cable.
3. Step 3
  A digital signal only has to be recognised as 'high' or 'low'. Even after noise is added it can be regenerated — cleaned back to a perfect series of 1s and 0s — so the noise is removed. An analogue signal cannot be cleaned in this way because noise becomes part of the continuously varying signal.
Answer
(a) Analogue varies continuously; digital has only two values (1/0) and changes in steps. (b) A digital signal can be regenerated to remove noise, so it arrives accurately; an analogue signal keeps any noise it picks up.
10Benefits of digital signalling
Extended• digital, signal regeneration
Question
State two benefits of sending information as a digital signal rather than an analogue signal, and explain how signal regeneration provides them.
Step-by-step solution
1. Step 1
  Benefit 1 — increased range. A weak, noisy digital signal can be regenerated at intervals along the route back to a clean 1s-and-0s signal, so it can be sent over much greater distances without loss of quality.
2. Step 2
  Benefit 2 — increased rate of transmission. Digital signals allow more information to be sent per second (a higher data rate), so more data can be transmitted in a given time.
3. Step 3
  Both come from regeneration: because the signal only has two levels, repeaters can rebuild it accurately, keeping it clear over long distances and at high data rates.
Answer
Digital signalling gives (1) an increased rate of transmission of data and (2) an increased range, because the two-level signal can be accurately regenerated by repeaters to remove noise.
Examiner tip
Mark schemes want the words 'increased rate of transmission' and 'increased range', linked to 'accurate signal regeneration'.
11Satellite communication — low-orbit vs geostationary
Core• microwaves, satellites
Question
Communication with artificial satellites is mainly by microwaves. (a) State why microwaves are used rather than visible light. (b) State which type of satellite is used by (i) some satellite phones and (ii) direct broadcast satellite television.
Step-by-step solution
1. Step 1
  (a) Microwaves can pass through the atmosphere (and clouds) to reach satellites and only need a short aerial; visible light would be scattered and blocked by cloud.
2. Step 2
  (b)(i) Some satellite phones use low-orbit (low Earth orbit) artificial satellites.
3. Step 3
  (b)(ii) Direct broadcast satellite television (and some satellite phones) use geostationary satellites, which stay above a fixed point on the Earth.
Answer
(a) Microwaves pass through the atmosphere and need only a short aerial. (b)(i) low-orbit satellites; (ii) geostationary satellites.
12Beyond 0625 — Intensity-distance gradient (inverse-square law)
ChallengeGraph or diagram• graph, synoptic
Question
The intensity $I$ of microwaves from a small source is measured at distance $d$ from the source. A graph of $I$ (y-axis) against $1/d^{2}$ (x-axis) is a straight line through the origin with gradient $0.36\,\text{W}$ . (a) State what this implies physically. (b) Use the gradient to find the intensity at $d = 0.30\,\text{m}$ .
Step-by-step solution
1. Step 1
  (a) Straight line through origin → $I \propto 1/d^{2}$ → an inverse-square relationship, consistent with energy spreading out over the surface of a sphere of radius $d$ .
2. Step 2
  Gradient $= I \times d^{2}$ , so $I = (\text{gradient})/d^{2}$ .
  $I = \dfrac{0.36}{(0.30)^{2}} = \dfrac{0.36}{0.09} = 4.0\,\text{W/m}^{2}$
Answer
(a) Inverse-square law: $I \propto 1/d^{2}$ (energy spreads over a spherical surface). (b) $I = 4.0\,\text{W/m}^{2}$ .
Examiner tip
Enrichment beyond Cambridge IGCSE 0625 — the inverse-square law $I \propto 1/d^{2}$ for radiation intensity is NOT in the 0625 syllabus (§3.3 covers the EM spectrum, uses and hazards only). It belongs to AS/A-level physics. This example is kept as enrichment for graph-interpretation practice, but the inverse-square relationship will not be examined on 0625.
13Beyond 0625 — Rank radiations by photon energy
ChallengeIdentify & classify• synoptic, photon
Question
Four EM waves are given: green visible light, microwaves, X-rays, infrared. (a) Rank them in order of INCREASING photon energy. (b) Use this ranking to explain why X-rays can pass through soft tissue while visible light cannot.
Step-by-step solution
1. Step 1
  Photon energy increases with frequency. Order of frequency low → high: microwaves < IR < visible < X-rays.
2. Step 2
  Therefore order of photon energy: microwaves < IR < visible < X-rays.
3. Step 3
  X-ray photons carry far more energy than visible-light photons. They penetrate soft tissue (electrons in atoms cannot absorb a full X-ray photon as efficiently) but are absorbed by denser bone, allowing a shadow image to form. Visible-light photons are absorbed by the very first cell layers of the skin.
Answer
(a) microwaves < IR < visible < X-rays. (b) X-rays have far more energy per photon; they pass through soft tissue but are absorbed by bone.
Examiner tip
Enrichment beyond Cambridge IGCSE 0625 — the concept of a 'photon' and ranking radiations by photon energy are NOT in the 0625 syllabus. 0625 §3.3 only requires the order of the EM spectrum by frequency/wavelength, typical uses and harmful effects — it does not introduce photons. Photon energy belongs to AS/A-level physics. This example is kept as enrichment; the 0625-relevant idea is simply that higher-frequency radiation tends to be more harmful. It will not be examined on 0625.

Model Answers — Electromagnetic Spectrum

High-scoring sample answers for electromagnetic spectrum on the Cambridge IGCSE 0625 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.

Question 1
Paper 2/4 short-answer style1 mark
List the seven regions of the electromagnetic spectrum in order of increasing frequency.
Model answer
Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
Why this scores
One mark for the complete correct order. Increasing frequency means decreasing wavelength — radio has the longest wavelength, gamma the shortest.
Question 2
Paper 2/4 style2 marks
All electromagnetic waves travel at the same speed in a vacuum. (a) State this speed. (b) Calculate the wavelength of a radio wave of frequency $100\,\text{MHz}$ .
Model answer
(a) $c = 3.0 \times 10^{8}\,\text{m/s}$ .

(b) $\lambda = \dfrac{c}{f} = \dfrac{3.0 \times 10^{8}}{100 \times 10^{6}} = \dfrac{3.0 \times 10^{8}}{1.0 \times 10^{8}} = \mathbf{3.0\,\text{m}}$ .
Why this scores
One mark for $c = 3.0 \times 10^{8}\,\text{m/s}$ , one for $\lambda = 3.0\,\text{m}$ . Converting $100\,\text{MHz}$ to $1.0 \times 10^{8}\,\text{Hz}$ is the step most often slipped.
Question 3
Paper 2/4 style3 marks
State one use for each of the following: (a) infrared, (b) ultraviolet, (c) X-rays.
Model answer
(a) Infrared: thermal imaging cameras (or TV remote controls, short-range data links, grills/cooking).

(b) Ultraviolet: sterilising water (or security marking with fluorescent ink, detecting forged banknotes, sun-tanning beds).

(c) X-rays: medical imaging of bones (or airport security scanners).
Why this scores
One mark for a correct use of each region. A common error is giving 'cooking' as a use of UV — cooking is infrared or microwaves.
Question 4
Paper 4 structured style4 marks
Ultraviolet, X-rays and gamma rays can all be harmful to people. (a) State one harmful effect of ultraviolet and one of X-rays. (b) Explain why these high-frequency waves are more dangerous than visible light.
Model answer
(a) Ultraviolet can cause skin damage (sunburn and skin cancer) and eye damage (cataracts). X-rays are ionising and can damage or kill cells and cause mutations / cancer with prolonged exposure.

(b) These waves have a higher frequency than visible light, so they carry more energy. UV, X-rays and gamma rays have enough energy to be ionising — they can remove electrons from atoms and damage molecules such as DNA in living cells. Visible light does not carry enough energy to ionise, so it is not harmful in this way.
Why this scores
Four marks: one harmful effect of UV (1) and of X-rays (1); higher frequency means higher energy (1); high-energy waves are ionising / damage cells and DNA (1). The danger comes from the energy carried, which increases with frequency.
Question 5
Paper 4 explanation style5 marks
A sound is to be transmitted along a long cable as an electrical signal. (a) State the difference between a digital signal and an analogue signal. (b) Explain why the signal is received more accurately if it is sent in digital form.
Model answer
(a) An analogue signal varies continuously and can take any value; a digital signal has only two values (high/low, or 1 and 0) and changes in steps — it is not continuous.

(b) As any signal travels along the cable it picks up unwanted noise and is weakened (attenuated). A digital signal only has to be recognised as 'high' or 'low', so even after noise is added it can be regenerated — rebuilt back into a clean series of 1s and 0s, removing the noise. An analogue signal cannot be cleaned in this way because the added noise becomes part of the continuously varying signal, so errors build up.
Why this scores
Five marks: analogue varies continuously (1); digital has two values/steps (1); signals pick up noise / are attenuated (1); digital can be regenerated to remove noise (1); analogue keeps the noise (1). The key advantage is accurate regeneration of the two-level signal.
Question 6
Paper 4 multi-part structured style6 marks
(a) Explain why microwaves, rather than visible light, are used to communicate with satellites. (b) A satellite microwave has a frequency of $1.2 \times 10^{10}\,\text{Hz}$ ; calculate its wavelength. (c) State the difference between a low-orbit satellite and a geostationary satellite, and which type is used for direct broadcast satellite television.
Model answer
(a) Microwaves can pass through the atmosphere (and clouds) with little absorption to reach the satellite, and need only a short aerial. Visible light would be scattered and blocked by clouds, so it would not reliably reach the satellite.

(b) $\lambda = \dfrac{c}{f} = \dfrac{3.0 \times 10^{8}}{1.2 \times 10^{10}} = \mathbf{0.025\,\text{m}}$ ( $= 2.5\,\text{cm}$ ).

(c) A low-orbit satellite orbits close to the Earth and moves quickly across the sky (its position changes). A geostationary satellite orbits high above the equator once per day, so it stays above a fixed point on the Earth. Direct broadcast satellite television uses geostationary satellites, so the receiving dish can point at a fixed position.
Why this scores
Six marks: microwaves pass through the atmosphere (1) and need a short aerial / visible light is scattered by cloud (1); wavelength $0.025\,\text{m}$ (1+1 for working and answer); low-orbit moves vs geostationary stays fixed above one point (1); TV uses geostationary (1).

Key Formulae — Electromagnetic Spectrum

The formulae you need to memorise for electromagnetic spectrum on the Cambridge IGCSE 0625 paper, with every variable defined in plain English and a note on when to use it.

Speed of EM waves
$c = 3.0 \times 10^{8}\,\text{m/s}$
When to use
Any EM wave in a vacuum (or approximately in air).

Key Definitions and Keywords — Electromagnetic Spectrum

Definitions to memorise and the exact keywords mark schemes credit for electromagnetic spectrum answers — sharpened from recent examiner reports for the 2026 0625 sitting.

Electromagnetic spectrum
Examiner keyword
Continuous range of EM waves arranged by frequency / wavelength: radio, microwave, IR, visible, UV, X-ray, gamma.
Photon energy (beyond the 0625 syllabus)
Energy of an EM 'particle' (photon) increases with frequency. NOTE: photons are AS/A-level content and are NOT in the 0625 syllabus — for 0625 it is enough to know that higher-frequency radiation tends to be more harmful. Included here as enrichment only.
Ionising radiation
Examiner keyword
Radiation with enough energy to remove electrons from atoms. UV (some), X-rays and gamma are ionising.
Analogue signal
Examiner keyword
A signal that varies continuously and can take any value.
Digital signal
Examiner keyword
A signal that has only two values (high/low, 1/0) and changes in steps; it can be regenerated to remove noise.

Common Mistakes and Misconceptions — Electromagnetic Spectrum

The traps other students keep falling into on electromagnetic spectrum questions — taken from recent Cambridge IGCSE 0625 examiner reports and mark schemes — and how to avoid them.

✕Saying X-rays travel faster than radio waves
0625/42 — recurring
Why it happens
Confusing 'energy' with 'speed'.
How to avoid it
All EM waves travel at the SAME speed in a vacuum: $c = 3.0 \times 10^{8}\,\text{m/s}$ .
✕Putting microwaves above visible light
Why it happens
Random ordering.
How to avoid it
Memorise: radio < microwave < IR < visible < UV < X-ray < gamma (increasing frequency).
✕Saying highest frequency has the longest wavelength
Why it happens
Inverting $c = f\lambda$ .
How to avoid it
Speed is constant → high $f$ ↔ low $\lambda$ (inversely proportional).
✕Listing 'cooking food' as a use of UV
Why it happens
Mixing IR / microwave with UV.
How to avoid it
Cooking → IR (grills) or microwaves (microwave ovens). UV → suntanning beds, sterilisation, fluorescence.

Electromagnetic Spectrum — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Band

Use

Hazard

Radio waves

TV, radio broadcasts

Generally safe

Microwaves

Cooking, satellite communication, mobile phones

Internal heating of body tissue

Infrared

Heaters, remote controls, thermal imaging

Burns to skin

Visible light

Vision, photography, optical fibre comms

High brightness damages retina

Ultraviolet

Sterilising, fluorescence, security marking

Skin cancer, sunburn, eye damage

X-rays

Medical imaging (broken bones), security scanners

Cell damage, mutation, cancer

Gamma rays

Cancer treatment (radiotherapy), sterilising medical instruments

Cell damage, mutation, cancer

Radio.

Use: terrestrial TV, FM/AM radio broadcasts.
Hazard: very low.

Microwaves.

Use: microwave ovens (resonates with water molecules), Wi-Fi, satellite TV, mobile phone signals.
Hazard: deep tissue heating; long-term exposure concerns near transmitters.

Infrared.

Use: TV remote controls, thermal imaging cameras (used by emergency services), heaters, optical fibres for short distances.
Hazard: skin burns from intense IR (e.g. heat lamps).

Visible.

Use: photography, vision, optical communications.
Hazard: bright light (especially lasers) damages the retina.

Ultraviolet.

Use: detecting fake banknotes, sterilising water/medical instruments, suntanning beds.
Hazard: sunburn, premature skin ageing, skin cancer, cataracts.

X-rays.

Use: medical imaging of bones; airport security scanners.
Hazard: ionises atoms in cells → cell damage / cancer with prolonged exposure. Hospital staff wear lead aprons.

Gamma.

Use: cancer treatment (radiotherapy), sterilising surgical instruments, food irradiation, detecting tumours.
Hazard: deeply penetrating; severe cell damage / cancer / death at high doses.

Tip. Cambridge mark schemes accept any reasonable use/hazard from the list — pick ones you can spell.

Electromagnetic Spectrum

Short Notes - Electromagnetic Spectrum

Detailed Study Notes

At a glance

What you’ll learn

Order of the spectrum

Shared properties of all EM waves

Uses and hazards — examples to memorise

Satellite communication

Digital and analogue signals

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

Question patterns to master — Electromagnetic Spectrum

1Order the EM spectrum

2Match an EM region to its use

3Speed of EM waves

4Biological effect of UV vs gamma

5Match each EM region to a common use

6Identify a region from a wavelength

7Dangers of high-frequency EM

8EM wave in vacuum — frequency calculation

9Digital versus analogue signals

10Benefits of digital signalling

11Satellite communication — low-orbit vs geostationary

12Beyond 0625 — Intensity-distance gradient (inverse-square law)

13Beyond 0625 — Rank radiations by photon energy

Speed of EM waves

Electromagnetic spectrum

Photon energy (beyond the 0625 syllabus)

Ionising radiation

Analogue signal

Digital signal

✕Saying X-rays travel faster than radio waves

✕Putting microwaves above visible light

✕Saying highest frequency has the longest wavelength

✕Listing 'cooking food' as a use of UV

Electromagnetic Spectrum — frequently asked questions

Electromagnetic Spectrum

Short Notes - Electromagnetic Spectrum

Detailed Study Notes

At a glance

What you’ll learn

Order of the spectrum

Shared properties of all EM waves

Uses and hazards — examples to memorise

Satellite communication

Digital and analogue signals

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

Question patterns to master — Electromagnetic Spectrum

1Order the EM spectrum

2Match an EM region to its use

3Speed of EM waves

4Biological effect of UV vs gamma

5Match each EM region to a common use

6Identify a region from a wavelength

7Dangers of high-frequency EM

8EM wave in vacuum — frequency calculation

9Digital versus analogue signals

10Benefits of digital signalling

11Satellite communication — low-orbit vs geostationary

12Beyond 0625 — Intensity-distance gradient (inverse-square law)

13Beyond 0625 — Rank radiations by photon energy

Speed of EM waves

Electromagnetic spectrum

Photon energy (beyond the 0625 syllabus)

Ionising radiation

Analogue signal

Digital signal