Question

The displacement of a travelling wave $y = C \sin \left( \frac{2\pi}{\lambda} (at - x) \right)$, where $t$ is time, $x$ is distance and $\lambda$ is the wavelength, all in S.I. units. Then the frequency of

• A. $\frac{2\pi \lambda}{a}$
• B. $\frac{2\pi a}{\lambda}$
• C. $\frac{\lambda}{a}$
• D. $\frac{a}{\lambda}$

Answer 1

Answer: (D)

$\frac{a}{\lambda}$

Answer 2

The general equation for a travelling wave is:

y = A sin(kx − ωt)

where:

A is the amplitude.

k is the wave number ($k = \frac{2\pi}{\lambda}$).

ω is the angular frequency ($\omega = 2\pi f$).

f is the frequency.

Comparing this with given equation: y = C sin($\frac{2\pi}{\lambda}$(at − x)), we get ω = $\frac{2\pi a}{\lambda}$.

Since ω = 2πf: 2πf = $\frac{2\pi a}{\lambda}$

$f = \frac{a}{\lambda}$