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

Options

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

Answer

B

Explanation

(b) `I = (E)/(R + r)`
`0.2 xx (10 + r) = 2.1`
`10 + r = (2.1)/(2) xx 10`
`r = 10.5 - 10 = 0.5 Omega`