Types of electromagnetic waves — AQA GCSE Physics

SPEC 4.6.2.1 • TYPES OF EM WAVES

The Electromagnetic Spectrum

Seven types of EM wave — from radio (longest wavelength) to gamma rays (shortest). All transverse, all travel at the speed of light in vacuum. Memorise the order; you'll use it for the rest of Module 6.

What EM Waves Are

You already met EM waves briefly in Lesson 6.01 as examples of transverse waves. Now we look at the full family.

Spec Wording

"Electromagnetic waves are transverse waves that transfer energy from the source of the waves to an absorber."

Two Things To Lock In

All EM waves are TRANSVERSE. The oscillations are perpendicular to the direction of energy transfer (same definition as from Lesson 6.01). This applies to radio, microwaves, visible light, gamma rays — every type.

EM waves transfer energy from a source (the Sun, an antenna, an X-ray tube) to an absorber (your eye, a TV aerial, a photographic plate). The wave itself is moving energy through space.

One Continuous Spectrum

EM waves cover an enormous range of wavelengths and frequencies — from kilometres long (radio) to smaller than an atom (gamma). But there are no gaps: it's one continuous spectrum.

Spec Wording

"Electromagnetic waves form a continuous spectrum and all types of electromagnetic wave travel at the same velocity through a vacuum (space) or air."

v = 3.0 × 10⁸ m/s

speed of all EM waves in vacuum (the "speed of light")

Critical Consequence

Because v is fixed in vacuum, the wave equation v = fλ tells us that frequency and wavelength must be inversely related. If wavelength halves, frequency doubles. The seven types differ in f and λ — never in speed.

The Seven Types SPEC ORDER

You must know these in order, from longest wavelength (lowest frequency) to shortest wavelength (highest frequency):

Remembering The Order

You will use this order constantly. A mnemonic helps you recall it under exam pressure.

Roman Men Invented Very Unusual X-ray Guns

LetterEM TypeFrequency (relative)Wavelength (relative)

RRadio wavesLOWESTLONGEST

MMicrowaves↓↓

IInfrared↓↓

VVisible light↓↓

UUltraviolet↓↓

XX-rays↓↓

GGamma raysHIGHESTSHORTEST

Pick One That Sticks

If "Roman Men..." doesn't work for you, invent your own. The point is to commit the order to memory so you don't have to derive it in the exam.

The Wavelength–Frequency Relationship

Because all EM waves travel at the same speed in vacuum, frequency and wavelength are inversely related. As you move across the spectrum, one increases while the other decreases.

↑ f

Higher frequency

(more waves/sec)

v constant

v = 3.0 × 10⁸ m/s

in vacuum

↓ λ

Shorter wavelength

(waves closer together)

The Maths

From v = fλ — all three examples below multiply to v = 3.0 × 10⁸ m/s:

Radio waves: f = 1.0 × 10⁸ Hz, λ = 3 m → 10⁸ × 3 = 3 × 10⁸ ✓

Visible light: f = 5.0 × 10¹⁴ Hz, λ = 6 × 10⁻⁷ m → 3 × 10⁸ ✓

Gamma rays: f = 3.0 × 10²⁰ Hz, λ = 1 × 10⁻¹² m → 3 × 10⁸ ✓

Each row has f × λ = 3.0 × 10⁸ m/s. Always — that's the constraint.

Visible Light — Red To Violet

Within visible light, the spec specifies the colour order: red to violet. Red has the longest wavelength; violet has the shortest. The familiar rainbow sequence is in between.

Spec-Required Knowledge

Spec explicitly says "visible light (red to violet)". Know the endpoints: red ≈ 700 nm (longest λ in visible) and violet ≈ 400 nm (shortest λ in visible). You don't need to recall the exact values, but you should know which end is which.

Wavelength Ranges

Approximate wavelength ranges for each type — useful for identifying an EM wave from its wavelength (a common exam task).

TypeApproximate wavelengthFamiliar example

Radiolonger than 0.1 m (10 cm)FM radio: ~3 m

Microwave0.1 m to ~1 mmMicrowave oven: ~12 cm

Infrared~1 mm to ~700 nmHeat from a fire: ~10 μm

Visible light700 nm (red) to 400 nm (violet)Green light: ~500 nm

Ultraviolet~400 nm to ~10 nmUV from the Sun: ~300 nm

X-rays~10 nm to ~0.01 nmMedical X-rays: ~0.1 nm

Gamma raysshorter than ~0.01 nmNuclear emissions: 10⁻¹² m

Quick Conversions

1 nm = 1 × 10⁻⁹ m | 1 μm = 1 × 10⁻⁶ m | 1 mm = 1 × 10⁻³ m. Always convert to metres before substituting into v = fλ.

Energy Transfer Examples SPEC BULLET

The spec requires you to give examples that illustrate the transfer of energy by EM waves. The source emits the wave; the absorber receives the energy.

EM TypeSource (emits)Absorber (receives energy)

RadioBroadcast antennaYour radio aerial → speakers

MicrowaveMicrowave oven magnetronWater molecules in food → heat the food

InfraredHot object (the Sun, a fire, a heater)Your skin → warms you up

Visible lightThe Sun, a light bulb, an LEDYour eyes → vision; solar panel → electricity

UltravioletThe Sun, UV lampsSkin → tanning / burns; phosphors → fluorescence

X-raysX-ray tubePhotographic film / detector → medical image

GammaRadioactive nuclei (decay)Body tissue (cancer treatment); detectors

The Eye Sees Only Visible

Of the entire EM spectrum — radio waves longer than buildings, gamma rays smaller than atoms — your eyes can only see one narrow slice.

Spec Wording

"Our eyes only detect visible light and so detect a limited range of electromagnetic waves."

Why "Visible" Is Called Visible

It's circular but spec-accurate: visible light is the part of the EM spectrum we can SEE. Roughly 400–700 nm. Everything outside that — IR, UV, X-rays, radio — is invisible to us, even though it's just as much an EM wave.

Other Detectors

We use technology to "see" the rest: radio receivers for radio, IR cameras for heat, X-ray detectors for medical imaging. Each is tuned to a different part of the spectrum.

Applying v = fλ To EM Waves

The wave equation from Lesson 6.02 works for all waves — including EM. For EM waves in vacuum, v is always 3.0 × 10⁸ m/s.

v = f × λ

v = 3.0 × 10⁸ m/s • f in Hz • λ in m

Why This Matters

Questions often give you an EM wavelength (e.g. "300 nm") and ask you to identify the type or calculate the frequency. Both are common Paper 2 marks. You need the wavelength ranges from slide 8 AND the calculation skill from 6.02.

Unit Trap

EM wavelengths are usually given in nm (nanometres). Always convert: 1 nm = 1 × 10⁻⁹ m. Skip this step and your answer is off by 10⁹.

Worked Example

An ultraviolet wave has a wavelength of 300 nm. The speed of EM waves in vacuum is 3.0 × 10⁸ m/s.

Calculate the frequency of this UV wave. 3 marks

E

v = f × λ → rearrange to f = v / λ

S

Convert: 300 nm = 300 × 10⁻⁹ m = 3.0 × 10⁻⁷ m

f = (3.0 × 10⁸) / (3.0 × 10⁻⁷)

U

hertz (Hz)

A

f = 1.0 × 10¹⁵ Hz

Sanity check: a UV wave should have frequency in the order of 10¹⁵ Hz — well above visible (around 10¹⁴ Hz) and below X-rays (above 10¹⁶ Hz). The answer makes physical sense for UV. ✓

Examiner Alert

The Two Facts Students Drop Marks On

1. All EM waves are TRANSVERSE. Including radio waves, microwaves, X-rays — every single one. If you write "longitudinal" for any EM wave, the mark scheme rejects.

2. All EM waves travel at the SAME SPEED in vacuum: 3.0 × 10⁸ m/s. They differ in frequency and wavelength, NOT in speed. Saying "X-rays travel faster than radio waves" loses marks every time.

Multiple-Choice Trap (from Jun 2019 Q07.1)

A question asked which statement is correct as wavelength decreases across the spectrum. The correct answer must include: "the frequency increases AND the wave speed in air stays the same". Statements claiming speed changes are wrong every time.

Practical Implication

A radio wave and a gamma ray from a distant star arrive at Earth at the same time if they were emitted together. The "speed of light" applies to all EM, not just visible.

Weak Vs Strong — Speed Misconception

"State a similarity and a difference between radio waves and X-rays." (2 marks)

Weak — 0 or 1/2

Answer: "X-rays are faster than radio waves and have shorter wavelengths."

Why it fails: "X-rays are faster" is physics-wrong. Both travel at 3.0 × 10⁸ m/s in vacuum. The shorter-wavelength comparison would have scored — but the false claim about speed cancels confidence.

Strong — 2/2

Answer:

Similarity: both are transverse EM waves; both travel at 3.0 × 10⁸ m/s in vacuum. Difference: X-rays have a shorter wavelength (and higher frequency) than radio waves.

Universal Comparisons

For any two EM types: same speed in vacuum, both transverse. They only differ in frequency and wavelength.

Common Errors

Students often writeCorrect versionWhy it matters

"Some EM waves are longitudinal"ALL EM waves are transverseNo exceptions — radio to gamma

"Higher frequency = faster wave"Higher frequency = shorter wavelength; speed unchangedv is fixed in vacuum at 3.0 × 10⁸ m/s

Lists order wrong (e.g. swaps IR and UV)Use a mnemonic — R-M-I-V-U-X-GOrder is spec-required; lose marks on wavelength-to-type ID

Substitutes wavelength in nm without convertingConvert nm → m before substituting (×10⁻⁹)Answer off by 10⁹ — frequency comes out tiny

"EM waves need a medium to travel"EM waves travel through vacuum — that's why sunlight reaches usConflates with sound waves (mechanical, need a medium)

"Visible light is the only EM wave with colour"All EM waves have a wavelength/frequency; only visible is perceived as colour by our eyes"Colour" is biology, not physics

Practice Question

(a) Electromagnetic waves are described as transverse. State what is meant by a transverse wave. 1 mark

(b) List the seven types of EM wave in order of increasing frequency. 2 marks

(c) An EM wave has a wavelength of 5.0 × 10⁻⁷ m in vacuum. Calculate its frequency. Speed of EM waves = 3.0 × 10⁸ m/s. 3 marks

(d) Use the wavelength range table to identify which type of EM wave this is. 1 mark

(a) A wave where the oscillations (or vibrations) are perpendicular to the direction of energy transfer. [1 mark]

(b) Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays. [2 marks for fully correct order; 1 mark for one or two mistakes]

(c) E: f = v / λ. [1 mark]

S: f = (3.0 × 10⁸) / (5.0 × 10⁻⁷) [1 mark]

A: f = 6.0 × 10¹⁴ Hz[1 mark with unit]

(d) 5.0 × 10⁻⁷ m = 500 nm, which is within the visible light range (400–700 nm). So this is visible light (green, approximately). [1 mark]

Lesson Summary

Lesson 6.05 complete. The EM spectrum order is foundational — you'll use it in every Module 6 lesson from here.

7 types

in spec order

Transverse

all of them

3 × 10⁸

m/s in vacuum

✓ Checkpoint — You Can Now…

Recall that EM waves are transverse and transfer energy from source to absorber

State that EM waves form a continuous spectrum and all travel at 3.0 × 10⁸ m/s in vacuum or air

Name the seven types in spec order : radio, microwave, infrared, visible, UV, X-rays, gamma

Recall that wavelength decreases and frequency increases from radio → gamma

Know visible light goes from red (longest λ) to violet (shortest λ) , approximately 700 nm to 400 nm

Identify which EM type a wave belongs to from its wavelength range

Apply v = fλ to EM waves with v = 3.0 × 10⁸ m/s

Give examples of energy transfer by each EM type (source → absorber)

State that our eyes only detect visible light , a limited range

Next Up

Lesson 6.06 — Properties of EM waves 1: refraction (HT) and RP9. How EM waves bend when they cross a boundary, and the practical for investigating reflection and refraction.