Electromagnetic Spectrum

IGCSE Edexcel Physics
3.10–3.13 EM spectrum: order, properties, uses and hazards
Key Concepts: All EM waves are transverse and travel at $3.0 \times 10^8\,\text{m/s}$ in free space. Order from lowest to highest frequency: radio → microwave → infrared → visible → ultraviolet → X-ray → gamma. Higher frequency = higher energy = shorter wavelength.

Section A — The EM Spectrum

1. List the seven regions of the electromagnetic spectrum in order of increasing frequency. [2]
2. State two properties shared by all electromagnetic waves. [2]
3. State how wavelength changes as frequency increases across the EM spectrum. [1]
4. List the colours of the visible spectrum in order from longest to shortest wavelength. [2]

Section B — Uses and Hazards

5. Complete the table of EM radiation uses. [7]
RegionOne use
Radio waves
Microwaves
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
6. Explain one harmful effect of each of the following: [4]

a) Ultraviolet radiation

b) X-rays

c) Gamma radiation

d) Microwaves

Section C — Calculations

7. A microwave oven uses microwaves of frequency $2.45 \times 10^9\,\text{Hz}$. Calculate the wavelength. ($c = 3.0 \times 10^8\,\text{m/s}$) [3]
8. An X-ray has wavelength $1.0 \times 10^{-10}\,\text{m}$. Calculate its frequency. [3]

Total marks: 24

Mark Scheme

1. Radio, microwave, infrared, visible, ultraviolet, X-ray, gamma [2 — 1 mark if 5–6 correct, 2 marks if all 7 in correct order]
2. Any two: all transverse; all travel at $3.0 \times 10^8\,\text{m/s}$ in free space; all transfer energy; all can travel through a vacuum [2]
3. Wavelength decreases (as frequency increases) [1]
4. Red, orange, yellow, green, blue, indigo, violet [2 — 1 mark if 5–6 correct]
5. Any correct use for each region, e.g.: Radio — TV/radio broadcasting; Microwave — cooking/satellite communication; Infrared — remote controls/thermal imaging; Visible — photography/human vision; UV — sterilisation/detecting forged banknotes; X-ray — medical imaging/airport security; Gamma — cancer treatment/sterilising medical equipment [7 — 1 mark each]
6. a) UV: skin cancer / sunburn / eye damage [1]; b) X-rays: ionise cells / cause cancer with high doses [1]; c) Gamma: ionising radiation damages DNA / causes cancer or mutation [1]; d) Microwaves: absorbed by water in body tissue, causing heating [1] [4]
7. $\lambda = c/f = (3.0 \times 10^8)/(2.45 \times 10^9) \approx 0.122\,\text{m}$ (about 12 cm) [3]
8. $f = c/\lambda = (3.0 \times 10^8)/(1.0 \times 10^{-10}) = 3.0 \times 10^{18}\,\text{Hz}$ [3]