Eur. Phys. J. Plus (2019) 134: 277
https://doi.org/10.1140/epjp/i2019-12790-y

Regular Article

Maxwell's equal-area law with several pairs of conjugate variables for RN-AdS black holes

¹ Department of Physics, Shanxi Datong University, 037009, Datong, China
² Institute of Theoretical Physics, Shanxi Datong University, 037009, Datong, China

^* e-mail: huaifan.li@stu.xjtu.edu.cn

Received: 7 January 2019
Accepted: 15 March 2019
Published online: 20 June 2019

Abstract

In this paper, using Maxwell's equal-area law we study the phase transition of charged AdS black holes by choosing different independent conjugate variables. As is well known, the phase transition can be characterized by the state function of the system, the determination of the phase transition point has nothing to do with the choice of independent conjugate variables. To study the thermodynamic properties of AdS black holes we give the conditions under which the independent conjugate variables are chosen. When the charge of the black hole is invariable, according to the conditions we find that the phase transition is related to the electric potential and the horizon radius of the charged black hole. Keeping the cosmological constant as a fixed parameter, the phase transition of the charged AdS black hole is related to the ratio of the event horizon to the cosmological constant of black holes.