The internal resistance of a `2.1 V` cell which gives a current `0.2 A` through a resistance of `10 Omega`

Options

A. `0.8Omega`
B. `1.0Omega`
C. `0.2Omega`
D. `0.5Omega`

Answer

D

Explanation

`I=(epsilon)/(R+r)`
or `IR+Ir=epsilon`
Here, `R=10Omega,r=?`
`epsilon=2.1V,I=0.2A`
`therefore 0.2xx10+0.2xxr=2.1`
`0.2r=0.1orr=(1)/(2)=0.5Omega`