Physics · Both
Waves – Properties & the EM Spectrum
Transverse and longitudinal waves, wave equation, electromagnetic spectrum and uses/dangers.
Waves transfer energy without transferring matter. Know the wave equation and the order of the electromagnetic spectrum.
Wave types and the wave equation
• **Transverse** – oscillations perpendicular to direction of travel (e.g. light, water waves)
• **Longitudinal** – oscillations parallel to direction of travel (e.g. sound)
**Wave speed** v = f λ
• v = speed (m/s)
• f = frequency (Hz)
• λ = wavelength (m)
Frequency = number of waves per second
Wavelength = distance between two corresponding points on adjacent waves
Worked example
A wave has frequency 50 Hz and wavelength 2 m. What is its speed?
Solution
v = f λ = 50 × 2 = **100 m/s**
Electromagnetic spectrum
Order of increasing frequency / decreasing wavelength:
Radio → Microwave → Infrared → Visible light → Ultraviolet → X-rays → Gamma
All EM waves travel at the same speed in a vacuum (3 × 10⁸ m/s).
**Uses / dangers (examples):**
• Radio – broadcasting
• Microwave – cooking, communications
• Infrared – remote controls, thermal imaging
• UV – can cause skin cancer; used in sterilisation
• X-rays – medical imaging; ionising
• Gamma – cancer treatment; highly ionising
Practice questions
Try these without looking at the answers first.
Q1.v = f λ. f = 200 Hz, λ = 0.5 m. Speed?
Show answer
100 m/s
Q2.Is sound transverse or longitudinal?
Show answer
Longitudinal
Q3.Which EM wave has the highest frequency?
Show answer
Gamma