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

Options

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

Answer

B

Explanation

Current `l=(E )/(R+r)` or `E = l (R+r)`
`2.1=0.2(10+r) rArr 10 + r(2.1)/(2)xx10`
`therefore " "` Resistance `r=10.5-10=0.5 Omega`