Question

A cell of emf E is connected with an external resistance R, then p.d. across cell is V. The internal resistance of cell will be ________ .

Answer 1

Answer:

The electromotive force (e) or e.m.f. is the energy provided by a cell or battery per coulomb of charge passing through it, it is measured in volts (V). It is equal to the potential difference across the terminals of the cell when no current is flowing.

E = I(R+r)

E = electromotive force in volts, V

I = current in amperes, A

R = resistance of the load in the circuit in ohms,

r = internal resistance of the cell in ohms.

That is, E = IR+Ir, E = V + Ir.

Rearranging the equation we get, r=

R

E−V

.

Substituting I=V/R in the above equation, we get, r=

R

V

E−V

=

V

(E−V)R

.

Hence, internal resistance r=

V

(E−V)R

.