Internal battery resistance: When a 20.0-ohm resistor is connected across the terminals of a 12.0-V battery, the voltage across the terminals of the battery falls by 0.300 V. What is the internal resistance of this battery?
A) 3.60 Ω
B) 1.56 Ω
C) 0.98 Ω
D) 0.30 Ω
E) 0.51 Ω

Question

Quizplus · Accepted Answer

The internal resistance of the battery can be found using the formula $V = IR + Ir$, where $V$ is the terminal voltage without any external load (12.0 V), $I$ is the current, $R$ is the external resistance (20.0 ohms), and $r$ is the internal resistance of the battery. The voltage drop when the resistor is connected indicates the voltage across the external resistor is $12.0V - 0.300V = 11.7V$. The current $I$ can be found by $I = \frac{V}{R} = \frac{11.7V}{20.0\Omega}$. Substituting back to find $r$, we get $r = \frac{V - IR}{I}$, which calculates to approximately $0.51 \Omega$.

Internal Battery Resistance: When a 20