The potential difference between the terminals or a battery is 10 V and internal resistance `1 Omega` drops to 8 V when connected across an external resistor . Find the resistance of the external resistor.

Options

A. 40 `Omega`
B. 0.4 `Omega`
C. `4 M Omega`
D. `4 Omega`

Answer

D

Explanation

`4 Omega`
Putting I = `(E)/(R + r)` in V = IR
`therefore V = (ER)/(R +r)`
`therefore 8 = (10xx R)/(R + 1)`
`therefore 8R + 8 = 10 ` R
`therefore ` 2 R =8
`therefore R = 4 Omega`