The physics of the optical light curve in supernovae

We present a new formula which models the rate of decline of supernovae (SN) as given by the light curve in various bands. The physical basis is the conversion of the flux of kinetic energy into radiation. The two main components of the model are a power law dependence for the radius--time relation and a decreasing density with increasing distance from the central point. The new formula is applied to SN 1993J, SN 2005cf, SN 1999ac, and SN 2001el in different bands.