Question

A potentiometer wire of length 10 m and a resistance 30 Ω is connected in series with a battery of emf 2.5 V and internal resistance 5 Ω and an external resistance R. If the fall of potential along the potentiometer wire is 50 μV/mm, the value of R is (in Ω)

• A. 115
• B. 80
• C. 50
• D. 100

Answer 1

Answer: (A)

115

Answer 2

By using $x = \frac{e}{(R + R_{h} + r)}.\frac{R}{L}$

⇒ $\frac{50 \times 10^{- 6}}{10^{- 3}} = \frac{2.5}{(30 + R + 5)} \times \frac{30}{10}$ ⇒ R = 115