(i) A student thinks that the battery in the gure has a non-negligible internal resistance. The student measures the potential difference across the battery as 9 V when it is not connected to any other circuit elements. The student then connects the circuit shown below, where the battery is represented by the circuit elements in the dashed box. The voltmeter indicates that the potential difference across one resistor is 4 V. Calculate the internal resistance of the battery. 209 ZO