In potentiometer experiment, a cell is balanced by length 120cm. When a cell is shunted by resistance of `5Omega`, the balancing length is 80 cm. The internal resistance of cell is

Options

A. `2.5Omega`
B. `3Omega`
C. `4Omega`
D. `5Omega`

Answer

A

Explanation

`l_(1)=120cm, R_(1)=5Omega, l_(2)=80 cm, r_(1)=?`
`r_(1)=R_(2)((l_(1)-l_(2))/(l_(2)))`
`=((120-80)/(80))=(5xx40)/(80)=(200)/(80)=2.5 Omega`.