When the switch is open in lowerpoint loop of a potentiometer, the balance point length is `60 cm`. When the switch is closed with a known resistance of `R=4Omega` the balance point length decreases to `40 cm`. Find the internal resistance of the unknown battery.

Answer

`2Omega`

Explanation

Using the result
`r=R(l_1/l_2-1)`
`=4((60)/(40)-1)`
`=2Omega`