IBDP Physics 5.3 – Electric cells: IB Style Question Bank SL Paper 1


For a real cell in a circuit, the terminal potential difference is at its closest to the emf when

A the internal resistance is much smaller than the load resistance.

B a large current flows in the circuit.

C the cell is not completely discharged.

D the cell is being recharged.


Ans: A

Potential difference and emf are two different quantities whose magnitudes may be equal in certain conditions. The emf is the work done per unit charge by the battery force Fb which is nonelectrostatic in nature. The potential difference originates from the electrostatic field created by the charges accumulated on the terminals of the battery.

The terminal potential difference of a cell is equal to the emf of the cell when:

 The cell is an open circuit.                      
 The internal resistance of the cell is zero.
 The load resistance much greater than internal resistance