In a potentiometer experiment, the null point is obtained at 140 cm for a cell of e.m.f. 1.2 V. With another cell of unknown e.m.f., the null point is obtained at 210 cm. The unknown e.m.f. is

Options

A. 1.5 V
B. 1.6 V
C. 1.8 V
D. 2 V

Answer

C

Explanation

`(E_(2))/(E_(1))=(l_(2))/(l_(1))=(210)/(140)=(3)/(2)`
`therefore E_(2)=(3)/(2)xx1.2 =1.8 V`