Ohm's law for a complete circuit – internal resistance

PhysicsElectricity & CircuitsAges 16–17

A closed circuit made of a source (EMF E, internal resistance r) and a rheostat R. Drag the slider directly on the circuit diagram to see I = E/(R + r), terminal voltage U = IR = E − Ir, power P = I²R, and efficiency H = U/E change; the P(R) graph shows the external power peaks when R = r. The electron flow speeds up or slows down with I.