Question

A 9 V battery delivers 180 mA current when battery is connected to 30 $\Omega$ load. Find internal resistance of battery ?

• A. 10 $\Omega$
• B. 20 $\Omega$
• C. 30 $\Omega$
• D. 40 $\Omega$

Answer 1

The correct option is B 20 $\Omega$

$i=\frac{V}{R+r}\Rightarrow r=\frac{V}{i}-R=\frac{9}{180\times {10}^{-3}}-30=\frac{9}{18}\times {10}^2-30=50-30$
= 20 $\Omega$