Question

A deniel cell is balanced on 125 cm length of a potentiometer wire. When the cell is short circuited with a 2 Ω resistance the balancing length obtained is 100 cm. Internal resistance of the cell will be

• A. 1.5 Ω
• B. 0.5 Ω
• C. 1.25 Ω
• D. 4/5 Ω

Answer 1

Answer: (B)

0.5 Ω

Answer 2

By using $r = \frac{l_{1} - l_{2}}{l_{2}} \times R' \Rightarrow r = \frac{125 - 100}{100} \times 2 = \frac{1}{2} = 0.5\Omega$