Interactive Simulator · E.M.F. and internal resistance

Load the Cell

Draw more current from the cell and watch the terminal voltage fall below the e.m.f. by the lost volts Ir. A high internal resistance makes the cell sag under load.

Mission Predict the effect on the terminal p.d. of decreasing the external resistance. Streak 0Best 0
As the external resistance decreases, the terminal p.d.:
external R5.0 Ω
current I = E/(R+r)1.00 A
terminal p.d. V = E−Ir5.00 V
lost volts Ir1.00 V
E = 6.0 V is fixed. The terminal p.d. is the e.m.f. minus the lost volts inside: V = E − Ir.