ICSE Class 9 Answered

Potential diferance across a circuit is defined as the differance in the net potentials at two points in a circuit. Generally, the potential differance is measured across the terminals of the battery as they provide the maximum net value of potential differance. In a circuit, one point (say positive terminal) can be at a higher potential V1 and the other point(the negative terminal) can be at a lower potential V2.

Then the total potential differance across these two points is = V1 - V2

Which should be positive if V1 > V2 and negative if V1 < V2. However, their absolute value is always taken to be positive by applying modulus function across the expression.

i.e. |V1 - V2|

Since the potentials at these two points is none other than the voltage at that point, the SI units of the PD is the same as that of Potential i.e. V(volt).

Hope it answers your query :-)