In a potentiometer experiment of a cell of emf 1.25 V gives balancing length of 30 cm. If the cell is replaced by another cell, balancing length is found to be 40 cm. What is the emf of second cell ?

Options

A. `~=1.47` V
B. `~= 1.57` V
C. `~=1.37` V
D. `~=1.67` V

Answer

D

Explanation

As `(epsilon_(1))/(epsilon_(2))=(l_(1))/(l_(2))`
where `epsilon_(1)` and `epsilon_(2)` are the emfs of two cells and `l_(1)` and `l_(2)` are the corresponding balancing lengths of the potentiometer wire.
`:.epsilon_(2)=(l_(2))/(l_(1))epsilon_(1)`
Here, `epsilon_(1)=1.25V, l_(1)=30 cm, l_(2)=40 `cm
`:. epsilon_(2)= (40)/(30)xx1.25~~1.67` V