3 · IGCSE Physics
The electromagnetic spectrum
Drag along the spectrum from radio waves to gamma rays to see how wavelength and frequency change, what each region is used for and how it can harm you, while the speed in a vacuum stays the same.
Region–
Wavelength λ–
Frequency f–
f × λ (speed)–
Photon energy E = hf–
Uses:
Dangers:
c = f λ
c = 3.00 × 10⁸ m s⁻¹ in a vacuum for every region
E = h f, h = 6.63 × 10⁻³⁴ J s
Left to right: wavelength decreases, frequency and energy increase. Boundaries between regions are approximate; X-rays and gamma rays overlap and are told apart by how they are produced.
Try this
- Drag the marker from radio waves to gamma rays while watching the f × λ readout. What stays the same, and what does that tell you about the speed of every region?
- Find both ends of the visible region. Use c = fλ to work out the frequency of red light with λ = 7.00 × 10⁻⁷ m, then check it on the readout.
- A mobile phone signal has f = 1.80 × 10⁹ Hz. Predict its wavelength, then slide to that value and name the region it lies in.
Common error: higher-frequency waves do not travel faster – in a vacuum every region moves at c, so doubling f always halves λ (c = fλ).