Electric Circuits - EMF and Internal Resistance [IB Physics SL/HL]

This video explains the concepts of electromotive force (EMF), internal resistance, and terminal potential difference in electrical circuits. It begins by contrasting ideal cells with real cells, which possess internal resistance that affects total circuit resistance and current. Using a circuit model, the speaker demonstrates how to calculate total resistance, current, and "lost volts" due to internal resistance, leading to the terminal potential difference available to the external circuit. The video further explores the implications of short circuits and generalizes these concepts using an equation derived from the loop rule. It concludes by illustrating how to determine EMF and internal resistance from a graph of terminal potential difference versus current, highlighting that EMF is the y-intercept and internal resistance is the negative gradient.