Three identical cells each of 2 V and unknow internal resistance are connected in parallel. This combination is connected to a 5 ohm resistor. IF the terminal voltage across the cell is 1.5 volt, what is the internal resistance of each cell?

Explanation

Number of cells = n = 3
Internal resistance of each cell = r = ?
External resistance `= R=9Omega`
`V = 1.5 V`
E = EMF of each cell = 2 V
Net internal resistance of three cells in parallel is given by
`1/r_p=1/r+1/r+1/r=3/r`
`r_p = r/3`
Now `r_p=(E/V-1)R`
`r/3 = (2/(1.5)-1)9`
`r/3 = (0.5)/(1.5) xx9`
`r = 9 Omega`