From schwarzschild black hole to Kerr-Newman black hole

A falling-in physical particle in metric and electromagnetic tensor field of Schwarzschild and Kerr-Newman black hole is studied. It is concluded that the physical particle will not make the outer horizon smaller. This is coincident with the area theorem. It is well known that delta A greater than or equal to 0 and delta kappa less than or equal to 0 are the necessary condition for changing from nonextremal to extremal Kerr-Newman black hole. We demonstrate that the surface gravity (temperature) of a Kerr-Newman black hole cannot be reduced to zero in a finite sequence of physical interactions. This is coincident with the third law of black hole thermodynamics. We also consider the trend of area change in the evolution of near-extremal black hole. The effect of negative heat capacity and the entropy renormalization are discussed.