Distinguish between emf (E) and terminal voltage (V) of a cell having internal resistance r.

The concepts of electromotive force (emf) and terminal voltage are essential in understanding how a cell operates, especially when internal resistance is involved.

Electromotive Force (emf)

Emf, denoted as E, is the maximum potential difference that a cell can provide when no current is flowing. It represents the energy supplied by the cell per unit charge and is determined by the chemical reactions occurring within the cell.

Key Characteristics of Emf

• Measured in volts (V).
• Indicates the cell's ability to do work.
• Remains constant regardless of the load connected to the cell.

Terminal Voltage (V)

Terminal voltage, represented as V, is the actual voltage output of the cell when it is connected to a circuit and current is flowing. It is affected by the internal resistance of the cell.

Understanding Terminal Voltage

• Also measured in volts (V).
• Can vary depending on the current drawn by the circuit.
• Calculated using the formula: V = E - Ir, where I is the current and r is the internal resistance.

Comparison of Emf and Terminal Voltage

In summary, while emf is the potential difference without any load, terminal voltage reflects the actual voltage available to the circuit under load conditions. The difference between the two is primarily due to the internal resistance of the cell, which causes a voltage drop when current flows.