Question

For a cell terminal potential difference is 2.2 volt when circuit is open and reduced to 1.8V when cell is connected to a resistance of R = 5Ω. Determine internal resistance of cell –

• A. $\frac{10}{9}$Ω
• B. $\frac{9}{10}$Ω
• C. $\frac{11}{9}$Ω
• D. $\frac{5}{9}$Ω

Answer 1

Answer: (A)

$\frac{10}{9}$Ω

Answer 2

When ckt is open, P.D. = E = 2.2 volt.

i = $\frac{2.2}{r + 5}$ ; P.D. across cell = E – ir

1.8 = 2.2 – $\frac{2.2}{r + 5}$ × r ⇒ $\frac{2.2r}{r + 5}$ = 0.4

⇒ r = $\frac{20}{1.8} = \frac{10}{9}$Ω