Question

The SI unit of wavelength is _________
(A). cm
(B). dm
(C). m
(D). km

Answer 1

- Hint: While considering wavelength, we have to consider for what purpose the term wavelength is used for and also which quantity is being measured in the case of wavelength.

Complete step-by-step solution -

Usually, in wave mechanics, wavelength is the distance between two consecutive crests or two consecutive troughs. In simple words we can say that it is the distance at which the shape of the wave repeats itself. Usually, wavelength is denoted by a Greek letter called Lambda $\left(\lambda \right)$.
Given below is the graph of a sine wave, which is a periodic wave by nature. The distance between two consecutive crests is denoted by an orange line which is the wavelength.

So we are measuring the distance in this case. The SI unit of distance as we all know is metre (m).
So the answer to the question is option (C) – m
Additional Information:
Waves are of two types, 1) Transverse waves and 2) Longitudinal Waves
There are crests and troughs present in transverse waves while compressions and rarefactions are present in longitudinal waves.
While the wavelength in a transverse wave is the distance between two consecutive troughs or crests, the wavelength in longitudinal waves is defined as the distance between two consecutive compressions or rarefactions.

Note: Wavelength plays a huge role in physics. In quantum mechanics, if you know the wavelength of a matter-wave we can find the momentum associated with the wave.