Question

A travelling harmonic wave on a string is described by

What are the displacement and velocity of oscillation of a point at x = 1 cm, and t = 1 s? Is this velocity equal to the velocity of wave propagation?

Locate the points of the string which have the same transverse displacements and velocity as the x = 1 cm point at t = 2 s, 5 s and 11 s.

Answer 1

The velocity of the oscillation at a given point and time is given as:

Now, the equation of a propagating wave is given by:

Hence, the velocity of the wave oscillation at x = 1 cm and t = 1 s is not equal to the velocity of the wave propagation. 

Propagation constant is related to wavelength as:

Therefore, all the points at distances nλ (n = ±1,±2,....and so on), i.e. ± 12.56 m, ± 25.12 m, … and so on for x = 1 cm, will have the same displacement as the x = 1 cm points at t = 2 s, 5 s, and 11 s.