Question

Find potential difference between two points when a third charge is present

Answer 1

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.

We should first find the direction of the current to determine values ∑ε and ∑i.R. If you take the sign of batteries having same direction with current as “+” then you must take oppositely connected batteries

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 "-".

In the circuit given below, if the direction of the current is shown like below, then potential difference between the points A-B and C-B are
VAB=VB-VA= -ε2-(+i.R1+i.R2)

VCB=VB-VC= -ε3-(-i.R3)