Waves – AS Physics Revision


Sine waves of different frequency.

Sine waves of different frequency. (Photo credit: Wikipedia)

  • Transverse waves are the ones that go up and down as they go along, and look like a sine wave when you draw them (oscillation perpendicular to direction of travel)
  • [Longitudinal waves oscillate in the same direction they travel, so they’re sort of pressure waves, like sound waves (and difficult to draw)]
  • The amplitude is the maximum displacement from equilibrium, of a wave. How far it is from the middle, at its highest/lowest point, basically
  • The period is the time taken for one complete oscillation (to the top, to the bottom and back to where it started, not necessarily in that order)
  • The frequency is the number of oscillations per second

Measuring and Equation-ing

  • The symbol for wavelength is lambda, λ
  • Wavelength is measured in metres, m (often nanometres, nm)
  • The period is measured in seconds, s
  • The frequency is measured in hertz, Hz (often kilohertz, kHz)
  • Frequency and period are reciprocals: fT=1, f=1/T, and T=1/f, where f is the frequency and T is the period
  • That’s why Hz^-1 = s, and Hz = s^-1. Hertz are kind of ‘per-seconds’
  • The speed / velocity, v, of a wave is measured in metres per second, ms^-1 (when it’s velocity, it’ll have a direction attached, remember)
  • v=fλ is the wave equation. It’s useful. Remember it.
  • (I’m going to assume you know how to use it. Hint: substitute values in)

On Graphs and in Radians

  • Ever seen a graph of y=sin(x)?
  • It’s a transverse wave of amplitude 1
  • The period of the graph depends on whether you’re measuring the angles along the bottom in degrees or radians
  • See my AS Maths Revision post on radians if you don’t know what they are
  • The period of a sine wave in degrees is 360
  • The period of a sine wave in radians is 2 * Pi
  • If the scale along the bottom is in metres, it’s not a graph of y=sin(x) – it’s just a drawing of a perfect sine wave

About Matt

I like writing, filmmaking, programming and gaming, and prefer creating media to consuming it. On the topic of consumption, I'm also a big fan of eating.
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