Question

Define the emf of a cell in terms of the work done in moving a charge through the cell. Using Joule's law obtain the equation, $emf=I(R+r)$.

Answer 1

work done by cell in flowing a unit charge throughout the whole circuit is called as the emf of the cell.

EMF of the cell is given by the equation,

$E=\frac{w}{q}$

where,

w - work done by the cell

q - charge

Let "E" be the emf of cell,

"r" be the internal resistance

"R" be the external resistance

"I" be the current through the circuit

$E-Ir=V=IR$

$=IR+Ir$

$\therefore E=I(R+r)$