What is Kirchoff’s voltage law?

Kirchoff’s voltage law is based on the principle of conservation of energy. This requires that the total work done in taking a unit positive charge around a closed path and ending up at the original point is zero. 

This gives us our basic Kirchoff’s law as the algebraic sum of the potential differences taken round a closed loop is zero.

i.e. around a loop,  ΣVr= 0, where Vrare the voltages across the branches in the loop. 

va+ vb+ vc+ vd– ve= 0 

This is also sometimes stated as the sum of the emfs taken around a closed loop is equal to the sum of the voltage drops around the loop.