The document discusses key concepts related to electrical circuits including: 1. It defines electro motive force (EMF) as the maximum potential difference between electrodes when no current is drawn, and compares it to potential difference (P.D.) which is the difference in potential between any two points in a closed circuit. 2. It explains that the internal resistance of a cell depends on factors like the separation of electrodes, conductivity of the electrolyte, and electrode materials. 3. It describes how cells can be connected in series or parallel configurations and the effects on equivalent resistance, EMF, and current in each case.