What is the relationship between potential difference across the terminals of a cell and emf of the cell?

The relationship between the potential difference across the terminals of a cell and its electromotive force (emf) is fundamental in understanding how batteries and cells operate.

Defining Key Terms

Electromotive Force (emf) refers to the maximum potential difference a cell can provide when no current is flowing. It represents the energy supplied by the cell per unit charge.

Potential Difference is the voltage measured across the terminals of the cell when it is connected to a circuit and current is flowing. This value can be lower than the emf due to internal resistance.

Understanding the Relationship

• When a cell is not connected to a circuit, the potential difference equals the emf.
• As current flows, the potential difference decreases due to the internal resistance of the cell.
• The formula that relates these concepts is: V = emf - Ir, where V is the potential difference, I is the current, and r is the internal resistance.

Practical Implications

This relationship is crucial for understanding how efficiently a cell can deliver power. A significant drop in potential difference compared to the emf indicates that the cell is under load and may be losing energy due to internal resistance.

In summary, while the emf represents the ideal voltage of a cell, the potential difference reflects the actual voltage available for use in a circuit, influenced by the cell's internal characteristics.