AS physics past paper questions: Internal Resistance

In this video, we'll solve two questions on internal resistance from Edexcel AS physics past papers. A cell of emf E and internal resistance r is connected across a fixed resistor of resistance R. There is a current I in the circuit and a potential difference V across the fixed resistor. Which of the following is an expression for the lost Volts?

This question will help you understand how to find internal resistance of a cell connected in a series circuit.

The second question is a graphical understanding of the same concept. We will see how we can find internal resistance from a given graph. A cell of emf E and internal resistance r is connected across a variable resistance as shown. A student varied the current in the circuit using the variable resistor. The current I and the corresponding potential difference V across the cell were recorded. A graph was plotted of V against I. Which of the following statements about the graph is correct.