Waves
Wave basics
Waves transfer energy without transferring matter. SEC Physics tests wave terminology, the wave equation, reflection, refraction, diffraction and superposition.
- Transverse waves vibrate perpendicular to energy transfer (light); longitudinal waves vibrate parallel (sound).
- Amplitude = maximum displacement; wavelength = distance between adjacent in-phase points; frequency = oscillations per second (Hz); period T = 1/f.
- Wave equation: v = fλ; speed depends on the medium.
- Reflection: angle of incidence equals angle of reflection, measured to the normal. Refraction changes speed and wavelength; frequency stays constant. Diffraction is spreading at gaps or edges, most noticeable when the gap is about the same size as the wavelength.
- Superposition adds displacements; interference is constructive or destructive.
Worked example
A sound wave has frequency 170 Hz and travels at 340 m/s. Find its wavelength and period.
λ = v/f = 340/170 = 2.0 m.
T = 1/f = 1/170 ≈ 0.0059 s (5.9 ms).
Reasoning: the wave equation links speed, frequency and wavelength; period is the reciprocal of frequency, not wavelength divided by speed.
Traps
Confusing amplitude with wavelength; measuring angles from the surface instead of the normal; thinking frequency changes in refraction; using v = fλ with mixed units (Hz and kHz); assuming diffraction occurs only at very wide gaps.