A cell of e.m.f. ε and internal resistance r is used to send current to an external resistance R. Write expressions for (a) the total resistance of circuit, (b) the current drawn from the cell, (c) the p.d. across the cell, and (d) voltage drop inside the cell.

Given,

e.m.f. = ε

internal resistance = r

external resistance = R

(a) The total resistance of circuit = R + r

(b) The current drawn from the cell

I = $\dfrac{\text { e.m.f.of cell}}{\text { total resistance}}$ = $\dfrac{\bold{\varepsilon}}{\bold{(R + r)}}$

(c) the p.d. across the cell = V = IR

Substituting from above,

V = $\bold{\dfrac{\varepsilon}{(R + r)}}$ x R

(d) voltage drop inside the cell V = Ir

Substituting from above,

V = $\bold{\dfrac{\varepsilon}{(R + r)}}$ x r