Reciprocity theorem :

• The theorem state that when some amount of electromotive force (or voltage) is applied at one point (e.g.,in branch k,vk) in a passive linear network, that will produce the current at any other point (e.g.,branch m, im). 
• The same amount of current (in branch k,ik) is produced when the same electromotive force (or voltage)is applied in the new location (branch m,vm) , that is

Vk/im=vm/ik