Combination of Batteries: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Combination of Batteries. Understanding the underlying formula is key to arriving at the correct answer below:

Internal resistance is given by $r = R(\frac{E}{V} - 1)$. Substituting $E = 2.2 \text{ V}$, $V = 1.8 \text{ V}$, and $R = 5 \Omega$, we get $r = 5(\frac{2.2}{1.8} - 1) = 5(\frac{0.4}{1.8}) = 5(\frac{2}{9}) = \frac{10}{9} \Omega$.