The momentum of an electromagnetic wave inside a dielectric

• We discuss an approximation to treat electrodynamics of a dielectric material.
• We support the Abraham form for the electromagnetic momentum.
• We deduce Snell’s law from the conservation of the Abraham momentum.
• We show how to deal with the electric field discontinuity at the dielectric boundary.

The problem of assigning a momentum to an electromagnetic wave packet propagating inside an insulator has become known under the name of the Abraham–Minkowski controversy. In the present paper we re-examine this issue making the hypothesis that the forces exerted on an insulator by an electromagnetic field do not distinguish between polarization and free charges. Under this assumption we show that the Abraham expression for the radiation mechanical momentum is highly favored.