The balancing length for a cell is 560 cm in a potentiometer experiment. When an external resistance of 10 `Omega` is connected in parallel to the cell , the balancing length changes by 60 cm. If the internal resistance of the cell is `(n)/(10) Omega` the value of n is ....

Options

A. 10
B. 11
C. 12
D. 14

Answer

C

Explanation

12
Let, `epsilon` is emf of battery and , is internal resistance and x is potential gradient. when onJy battery is connected, then
`epsilon =560x " "` ....(1)
After connecting resistance ,
`(epsilon xx 10)/(10 + r) ` = (560x - 60) x = 500x ...(2)
From equation (1) and (2)
`(560 xx 10x)/(10 + r) = 500`x
`therefore 56 = 50 + 5r`
`therefore 6 = 5r `
`therefore r = 1.2 Omega`
`therefore (n)/(10) = 1.2 " " therefore n = 12 `