Question
The potential difference between the terminals of a 6.0V battery is 7.2V when it is being charged by a current of 2.0A. What is the internal resistance of the battery?
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Answer
$\text{V}=\in+\text{ir}$$\Rightarrow7.2=6+2\times\text{r}$
$\Rightarrow1.2=2\text{r}\Rightarrow\text{r}=0.6\Omega.$
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