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 δA≥0 andδκ≤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.