Intuition behind Snell's Law

Let me help provide some intuition behind Snell's Law. If you're not satisfied with just the intuition I'll show in a follow-up video how the geometry works to get Snell's Law First thing to understand with snell's law is what the index of refraction, n, is n is basically a measure of how fast travels through a medium Our baseline is n=1 for light traveling through space If light traveled half that fast through a medium, the medium would have n2=2 so the speed of light through the medium would be v2=cn2 Or half the speed of light in a vacuum Demo: So lets see how this would work for a plane wave So imagine we have a region with n=1 on top and n=2 in the gray region below the green line The plane wave is starting up here, propagating downward You can see when it hits this new medium, the wave slows down It has the same frequency because the phase at the line has to match But it has different wavelength If the wavelength on top is lambda_1 Then the wavelength on bottom is 𝜆2=𝜆1∗n1n2 , or .71 lambda_1 in this case Now imagine if this plane wave was incident at an angle The part of the wavefront that hits the medium first slows down While the part that hasn't hit it yet keeps going at normal speed The side slowing down causes the wavefront angle to shift And this wave front is perpendicular to the direction the beam is traveling So you can see up here the wavefront is like this, And propagation is perpendicular Now here the wavefront angle shifts since one side slowed down first And the propagation direction is perpendicular, so it also shift This gives rise to Snell's law, which states: n_1sin(\theta_1)=n_2sin(\theta_2) Where n_1 and n_2 are the refractive indecis' as discussed And theta_1 and theta_2 are the angles with respect to the normal line to the interface of the mediums So this is the basic intuition of how it works. If you're not completely satisfied with the inuition and want to really understand where this equation comes from, I'll show that in the next video. It's not that bad, just need a little geometry to show how we get this.