Two points are located at a distance of 10 m and 15 m from the source of oscillation. The period of oscillation is 0.05 sec and the velocity of the wave is 300 m/sec. What is the phase difference between the oscillations of two points? 

Here, T = 0.05 sec, v = 300 ms^-1 . 

Now $\lambda =\frac{v}{\mathcal{v}}=vT=\left(300\times 0.05\right)m$

$or \lambda =15 m$

Phase of the point at 10 m from the source

$=\frac{2\mathrm{\pi }}{\lambda }\times x=\frac{2\mathrm{\pi }}{15}\times 10=\frac{4\mathrm{\pi }}{3}rad$

Phase of the point at 15 m from the source

$\frac{2\mathrm{\pi }}{\lambda }\times x=\frac{2\mathrm{\pi }}{15}\times 15=2\mathrm{\pi } rad$

∴ The phase difference between the points

$=2\mathrm{\pi }-\frac{4\mathrm{\pi }}{3}=\frac{2\mathrm{\pi }}{3} \mathrm{rad}$