This awesome formula. It turns wave into particle and particle into wave.
(left to right)
Given a EM wave of wavelength(or freq), the wave poses a momentum which is a particle property. Hence EM wave falling on surface is like molecules hitting the surface , hen ce producing force and pressure. It can cause motion in space in particular and not on Earth where there are other forces that are more significant.
(right to left)
Given a particle having a large speed and therefore momentum would be seen as a wave having a wavelength. Such particles are like electrons and protons. When this electron or proton beam are incident on a "grating" which is crystalline solid produces diffraction pattern obeying equations using path diff = n(wavelength). Path difference simply means the difference in the path taken by two different directions travelled by the beam. Make sure you know the meaning of path difference because it is fundamental to interference whether it is constructive or destructive.
