Internal Resistance E r The battery produces an electromotive force (emf), E, however the electrons loose some of this energy in travelling through it. This is caused by internal resistance, r. When a current is drawn from a battery the potential difference across it is call the terminal potential difference, V T. E = V T + Ir Ir is sometimes known as the lost volts

Experiment 1 Find I for 5 different values of V T. E = V T + Ir V T = -Ir + E y = mx + c The gradient of the graph is – r The intercept is E V T In volts I in amps E r VTVT A R

Experiment 2 Find current for different values of load resistance, R R in  1 ÷ current in A -1 E = IR + Ir E = R + r R = E – r y = mx + c E is the gradient of the graph - r is the intercept I I E r A R

E = V T + Lost volts E = IR + Ir E = V T + Ir When battery is open circuit I = 0 so E = V T When battery is short circuited R = 0 so E = Ir Tutorial Questions 15 to 24 SAQs to page 30 Purple book Ex 4.5