Two identical cells of emf 1.5 V each joined in parallel provided supply to an external circuit cosisting of two resistances of `17 Omega` each joined in parallel. A very high resistance voltmeter reads. The teminal voltage of cells to be 1.4V. Calculate the internal resistance of each cell.

Explanation

Here, `epsilon = 1.5 V, R_(1)=R_(2)=17 Omega`,
V=1.4V
Resistance of external circuit, `R = (R_(1)R_(2))/(R_(1) +R_(2)) = (17 xx 17)/(17+17) = 8.5 Omega`
As two cells are connected in parallel, their effecticve emf, `epsilon=1.5V`,
their effective internal resistance,
`r'= (r xx r)/(r+r) = r/2`
Then `r'= ((epsilon - V)/(V))=R`
So `r/2 = ((1.5 - 1.4)/(1.4))8.5`
or `r=(1.0 xx8.5)/(2)xx2 = 1.2 Omega`