Interference equation

where λ = wavelength [m]
a = distance between sources [m]
x = distance between two successive antinodal/nodal lines [m]
D = distance between a and x [m]

Quiz:

1. When coherent sound waves propagate from two loudspeakers of 2 m apart, an observer can hear the loudest sound. The loudspeakers are connected to a source waves with a frequency of 500 Hz and observer walks a distance of 10 m in front of the loudspeakers. If the speed of sound is 300 ms^-1, what is the distance between two consecutive loudest sounds heard by the observer?

ans : 3 m