Question

You short-circuit a 18 volt battery by connecting a short wire from one end of the battery to the other end. if the current in the short circuit is measured to be 19 amperes, what is the internal resistance of the battery\

Answer 1

The relationship between the voltage and the current in the circuit is:
$\Delta V = RI$
where $\Delta V$ is the voltage difference, R the resistance of the circuit (and therefore, the resistance of the battery) and I the current flowing in the circuit. By using I=19 A and $\Delta V = 18 V$, we can find the internal resistance of the battery:
$R= \frac{\Delta V}{I}= \frac{18 V}{19 A}=0.95 \Omega$