Simulation · Physics · Class 12
Why the terminal voltage is less than the emf
From the lesson Cells, emf and internal resistance in Current Electricity. Change the values and watch what happens.
The idea behind it
NCERT § "Cells, emf, Internal Resistance"
- The emf ε of a cell is the potential difference between its terminals when no current is drawn; despite the name, it is a potential difference, not a force.
- Charge moving through the electrolyte meets an internal resistance r.
- When the cell drives a current I through an external resistor R, I = ε/(R + r) and the terminal voltage is V = ε − Ir, which is less than ε.
- The terminal voltage equals ε only on open circuit (I = 0), and falls to zero when the terminals are shorted, where the maximum current ε/r flows.
- Two readings with different external resistors give two equations that can be solved for both ε and r.
- The internal resistance of a car battery is very small, so it can supply the large currents a starter motor needs; dry cells have larger internal resistance.
More simulations in Current Electricity
4 more
Stretch a wire and watch its resistanceIn: Electric currents in conductors and Ohm's lawHow fast do electrons really move in a wire?In: Electron drift and where resistivity comes fromTwo cells: in series, in parallel, and one reversedIn: Cells in series and in parallelBalance a Wheatstone bridgeIn: Wheatstone bridge