Question

A source of potential difference V volt sends current I ampere in a circuit for time t second. Write expressions for

1. electrical energy supplied by the source and
2. electrical power spent by the source.

Answer 1

Potential difference V is the work done in moving a unit charge 

∴ Work was done in moving a charge Q through the pot. diff. V = QV

i.e. W = QV

but = `"Q"/"t" = "I"` or Q = It

∴ W = VIt

Work done = Electrical energy

(a) ∴ Electrical energy = VIt is the expression

(b) Power is the rate of doing W

P = `"W"/"t" = "VIt"/"t" = "VI"`

P = VI is the expression.