Dear student,
Potential  difference between two points in circuit is the energy lost by the  charge in being transferred from one point to another.  For example, potential difference between A and B is found with following formula;
VAB=VB-VA=∑ε-∑i.R
 
 
This formula shows the energy lost by charge moving from point A to point B.
If  the direction of the current and current passing through the resistor  are the same then we take i.R as "+", if they are in opposite directions  then we take i.R as "-".
VAB=VB-VA= -ε2-(+i.R1+i.R2)
VCB=VB-VC= -ε3-(-i.R3)
 

































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