What is the Difference Between Terminal Voltage and EMF?

The difference between terminal voltage and EMF lies in the condition of the circuit and the role of internal resistance. Here are the key differences:

• EMF (Electromotive Force): This is the potential difference between the two terminals of a battery or cell when no current is flowing through the circuit. It is an open-circuit voltage and is independent of the resistance of the electrical circuit but depends on the internal resistance of the circuit. EMF is always constant.
• Terminal Voltage: This is the potential difference between the two terminals of a battery or cell when a current is flowing through the circuit. It is a closed-circuit voltage and is less than the EMF. Terminal voltage is affected by the internal resistance of the battery and declines further as the battery is depleted or loaded down.

In summary, the main differences between EMF and terminal voltage are:

1. EMF is the potential difference when no current flows through the circuit, while terminal voltage is the potential difference when a current flows through the circuit.
2. EMF is independent of the resistance of the electrical circuit but depends on the internal resistance of the circuit, while terminal voltage is affected by both the internal and external resistances.
3. EMF remains constant, while terminal voltage decreases with the increase in internal resistance or load.

Comparative Table: Terminal Voltage vs EMF

The key difference between terminal voltage and EMF is that terminal voltage is a closed-circuit voltage, whereas EMF is an open-circuit voltage. Here is a table comparing the two:

In summary, terminal voltage is the potential difference measured across the terminals of a device when current is flowing, while EMF is the open-circuit potential difference between the terminals of a battery or cell. Terminal voltage can be affected by external resistance, while EMF remains constant regardless of external factors.