Question

For comparing the emfs of the two primary cells by potentiometer draw the circuit diagram and deduce the formula.

Answer 1

Comparison of Electromotive Forces of Two Primary Cells:

Suppose we have to compare e.m.f. of two primary cells E₁ and E₂ with the help of potentiometer. For this purpose we prepare the circuit diagram as figure.

First of all we press key K₁ and find out the balancing length l₁ for cell E₁. If k be the potential gradient of potentiometer wire, then
E₁ = kl₁ …………….. (1)

Now the key K₁ is removed and K₂ is fitted, then if l₂ be the new balancing length, then
E₂ = kl₂ …………….. (2)
From equations (1) and (2), we have
\(\frac{E_{1}}{E_{2}}=\frac{l_{1}}{l_{2}}\) ……………. (3)