Question

A battery with negligible internal resistance is connected with 10m long wire. A standard cell gets balanced on 600 cm length of this wire. On increasing the length of potentiometer wire by 2m, the null point will be displaced by,

• A. 200 cm
• B. 120 cm
• C. 720 cm
• D. 600 cm

Answer 1

The correct option is B 120 cm

By using $\frac{L_1}{L_2}=\frac{l_1}{l_2}\Rightarrow \frac{10}{12}=\frac{600}{l_2}\Rightarrow l_2=720cm$
Hence displacement = 720 – 600 = 120 cm