We will assume that the wave is moving in free space, thus, the velocity of the wave would be equal to the speed of light = 3 * 10^8 meters/sec
The velocity of the wave can be calculated using the following rule:
velocity = frequency * wavelength where:
velocity = 3 * 10^8 m/sec
frequency = 2500 Hz
wavelength is the unknown that we want to calculate.
Substitute with the givens in the above equation to get the wavelength as follows:
3 * 10^8 = 2500*wavelength
wavelength = 120 * 10^3 meters
