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The wave equation
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One equation links the speed, frequency and wavelength of every wave.
The wave equation
wave speed = frequency × wavelength, v = f × λ
v in m/s, f in Hz, λ in m.
Rearranged: f = v ÷ λ and λ = v ÷ f.
v in m/s, f in Hz, λ in m.
Rearranged: f = v ÷ λ and λ = v ÷ f.
Speed from distance and time
You can also use v = x ÷ t, where x is the distance a wave travels in time t.
Echoes
An echo travels to the object and back. To find the distance to a wall, halve the total distance the sound travels.
Sound travels at 340 m/s. An echo returns from a cliff after 1.5 s. How far away is the cliff?
- Total distance = speed × time = 340 × 1.5 = 510 m.
- The sound went there and back, so halve it.
- 510 ÷ 2 = 255 m
Answer: 255 m
v = f × λ. v = x ÷ t. For echoes, the sound travels there and back, so halve the total distance.
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