State the main properties of electromagnetic waves. Arrange radio waves, X-rays, visible light, microwaves and gamma rays in order of increasing frequency, and give one use of each.

1. 1 · Say what they are. EM waves are electric and magnetic fields vibrating together, produced by accelerated charges.
2. 2 · List the properties.
   • Transverse: E, B and the direction of travel at right angles; E = cB
   • Need no medium; speed c = 1/√(μ₀ε₀) = 3 × 10⁸ m s⁻¹ in vacuum
   • Slower in a medium: v = c/√(μᵣεᵣ)
   • Frequency stays the same in every medium
3. 3 · Draw the wave. [x, y and z axes; E as a sine curve in the x-z plane and B in the y-z plane, in step; z marked as the direction of travel]
4. 4 · Arrange them. Radio waves < microwaves < visible light < X-rays < gamma rays.
5. 5 · Give one use of each.
   • Radio waves: broadcasting
   • Microwaves: radar
   • Visible light: seeing
   • X-rays: finding fractures
   • Gamma rays: cancer treatment
6. 6 · Real life. A mobile phone, a TV remote and a hospital X-ray all use EM waves.
7. 7 · Close in one line. So, all EM waves share these properties and differ only in wavelength and frequency.

Scoring tip: Learn the spectrum in order; one wrong place in the order can cost the mark.