In an experment to determine the emf of an unknown cell, its emf is conparaed with a standard cell of known emf `epsi_(1)=1.12V`. The balanc point is obtained at 56cm. With standard cell and 80 cm with the unknown cell. Determine th eemf of the unknown cell.

Explanation

Here, `epsi_(1)=1.12V,l_(1)=56cm,l_(2)=80cm`
Using equation
`epsi_(1)=xl_(1)………………….(1)`
`epsi_(1)=xl_(2)...................(2)`
we get`epsi_(1)/epsi_(2)=l_(1)/l_(2)rArrepsi_(2)=epsi_(1)(l_(2)/l_(1))" or "epsi_(1)1.12(80/56)=1.6`
(b) To find current if resistance is known

`V_(1)-V_(C)=xf_(1)`
`1R_(1)=xl_(1),i=(xl_(1))/R_(1)`
Similarly, we can find the value of `R_(2)` also.
Potentiometer is ideal voltmeter because it does not draw any current from circuit, at the balance point.