Snell's Law and Conservation of Energy
Assume the follow condition:
A Prism in a vacuum
Now shot a ray of light through the prism. We know through
observation that the light will slow relative to the refractive
index. However, when the ray of light leaves the prism it speed
back up to 3.0x 10^8 m/s when no additional energy is added to the
system. How can this be?
I know that the conservation of energy must be true, so what am I missing?
A photon is massless and hence its energy cannot be equated to
mass*(velocity*velocity)/2. Instead it is described by Planck's
constant times the frequency. The frequency (and hence the energy)
does not change when the light goes from vacuum into glass.
Click here to return to the Physics Archives
Update: June 2012