The emf of a cell is `epsilon` and its internal resistance is r. its terminals are connected to a resistance R. The potential difference between the terminals is `1.6V` for `R = 4 Omega`, and `1.8 V` for `R = 9 Omega`. Then,

Options

A. `epsilon=1V,r=1Omega`
B. `epsilon=2V,r=1Omega`
C. `epsilon=2V,r=2Omega`
D. `epsilon=2.5V,r=0.5Omega`

Answer

B

Explanation

Current in the circuit, `I=(epsilon)/(R+r)`
p.d. across cell = p.d. across `R=IR=(epsilonR)/(R+r)`
Set up two equations with the given data
`1.6=(4epsilon)/(4+r)" "…(i)`
`1.8=(9epsilon)/(9+r)" "…(ii)`
Solving equations (i) and (ii), we get `r=1Omega,epsilon=2V`