  Applying the relation between Euclidean on-shell action in the bulk and free
energy on the holographic screen to a test charged particle in the charged R-N
black hole, we show that not only gravity but also electromagnetic force can be
regarded as a sort of thermal force, which accomplishes the unification of
gravity and electromagnetism to some extent. In addition, taking into account
the fact that both the temperature and thermal force of the dual system are
measured at infinity, we argue that the dual holographic screen may be located
at infinity.
