Wave basics: amplitude, wavelength, frequency and speed
Physics · Key Stage 3 · The School
Four properties, one wave
AMPLITUDE is the maximum distance a point moves from its resting position — it sets how much energy the wave carries. WAVELENGTH is the distance from one point on a wave to the same point on the next repeat, measured in metres. FREQUENCY is how many complete waves pass a point each second, measured in hertz. FREQUENCY is separate from amplitude, but wavelength and frequency are linked through speed.
The wave equation
Wave speed = frequency × wavelength, usually written v = fλ. A wave travelling at 340 m/s with a frequency of 170 Hz has a wavelength of 340 ÷ 170 = 2 m. Rearrange the same equation to find any one of the three, given the other two — it is one relationship, not three separate formulas to remember.
Transverse and longitudinal
In a TRANSVERSE wave, the particles vibrate at right angles to the direction the wave travels — like light, or a wave shaken along a rope. In a LONGITUDINAL wave, the particles vibrate along the SAME direction the wave travels — like sound, moving as a series of squeezes and stretches. Both carry energy without carrying matter along with them.
A radio wave travels at 300,000,000 m/s with a frequency of 100,000,000 Hz. Its wavelength = speed ÷ frequency = 300,000,000 ÷ 100,000,000 = 3 m. Now try it the other way: a wave in water has a wavelength of 0.5 m and travels at 1 m/s. Its frequency = speed ÷ wavelength = 1 ÷ 0.5 = 2 Hz. Same equation, rearranged twice, finding a different missing piece each time.