Question

Why is the emf of a battery always slightly higher than the potential difference that it can provide to an electric circuit?

Answer 1

The electromotive force (emf) of a battery is always slightly higher than the potential difference (voltage) it provides to a circuit due to the internal resistance of the battery.

Here’s why:

1. Internal Resistance: Every battery has some internal resistance, which means it resists the flow of current inside itself. This internal resistance is caused by the materials inside the battery, like the electrolyte and the electrodes.
   

1. When no current flows: When the battery is not connected to any circuit (or if the circuit is open), there is no current, and the potential difference across the terminals is equal to the emf. The emf is the energy per unit charge that the battery can provide.
   

1. When current flows: Once the battery is connected to a circuit and current starts to flow, some energy is lost inside the battery due to its internal resistance. This loss reduces the potential difference across the battery’s terminals. The amount of voltage drop depends on the current and the internal resistance.
   

So, the emf is the maximum potential difference the battery can supply, while the potential difference measured across the terminals when a current is flowing is slightly lower because of the energy loss in overcoming the internal resistance. This is why the voltage you see in a circuit is always a bit less than the battery's emf.