 if I show you the water from the underside and then I point my flashlight my phone flashlight from this side you can see the surface of the water begins to shine it is in fact reflecting the light from my flashlight and you need the angle of incidence to be greater than a particular value which we call the critical angle now this critical angle can be determined from the refractive index of the denser medium with respect to the layer of medium if this value is mu then the critical angle is given by the sign inverse of one binding first by the scientist called Christian Huygens sound is a wave just like light and Snell's law is not something that is specific to light it is a general law that applies to all kinds of waves traveling in any medium the density change in the layers of the air causes this light to bend away from the normal because the air is being heated up by the ground