Two point charges and are separated by a distance in vacuum
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two point charges q1 and q2 are separated by a distance r in vacuum.
Answer the following questions:
(i) State the definition of electric potential at a point due to a point charge.
(ii) Starting from this definition, derive an expression for the electrical potential energy U of the system consisting of the two charges q1 and q2 placed r metres apart.
(iii) Show explicitly that electric potential has the SI unit volt (V) while electrical potential energy has the SI unit joule (J). Why are both these quantities scalars?
(iv) If the separation between the charges is doubled, by what factor does the potential energy of the system change? Justify your answer mathematically.