The wave velocity of a progressive wave is 480 ms−1 and the phase difference between the two particles separated by a distance of 12 m is 10800. The number of waves passing across a point in 1 sec is

Given , Velocity v=480 m/s Phase difference ϕ=1080∘                                   =1080×π180=6π Distance x=12 m Time t=1sec Number of waves passing n=? Phase difference ϕ=2πλ.x                             6π=2πλ×12                        ⇒λ=4 m As    v=nλ      480=n×4 ∴  n=120 Hz