In all progressive waves, energy travels through the medium in the direction in which the wave travels. Each particle of the medium has energy of vibration and passes energy on to succeeding particles.
In simple harmonic motion, the energy of the vibrating particle changes from kinetic to potential and back, with the total energy constant. We can find this constant energy E by finding the maximum kinetic energy.
Where f is the frequency and m is the mass of vibrating particle. If n is the number of particles per unit volume in the medium, then the energy per unit volume in the medium is given by
But mn = mass per unit volume = density (r)
The transfer of energy per unit time per unit area, perpendicular to the direction of motion of the wave, is called the intensity (I) of the wave. In unit time, the wave will have traveled a distance v. Therefore, the intensity of the wave is the energy, contained in a cylinder of unit area of cross section and a length numerically equal to the velocity v of the wave.
We find that the intensity is directly proportional to
- the square of the amplitude
- the square of the frequency
