Why the emf of a cell is always greater than the terminal voltage?
2 Answers
The electromotive force (emf) of a cell represents the maximum potential difference it can provide when no current is flowing. In contrast, the terminal voltage is the potential difference across the terminals of the cell when it is connected to a circuit and current is flowing.
The reason the emf is always greater than the terminal voltage can be attributed to two main factors:
1. **Internal Resistance**: All real cells have some internal resistance. When a current flows through the cell, a voltage drop occurs across this internal resistance. This drop reduces the voltage available at the terminals of the cell. The relationship can be described by the equation:
\[
V_{\text{terminal}} = \text{emf} - I \cdot r
\]
where \( I \) is the current and \( r \) is the internal resistance of the cell. As long as there is current flowing, the terminal voltage will be less than the emf.
2. **Load Conditions**: The terminal voltage also depends on the load connected to the cell. If the load draws a significant amount of current, the effect of internal resistance becomes more pronounced, leading to a larger difference between the emf and terminal voltage.
In summary, the terminal voltage is always less than the emf due to the voltage drop caused by the internal resistance of the cell when current flows.
The reason the emf is always greater than the terminal voltage can be attributed to two main factors:
1. **Internal Resistance**: All real cells have some internal resistance. When a current flows through the cell, a voltage drop occurs across this internal resistance. This drop reduces the voltage available at the terminals of the cell. The relationship can be described by the equation:
\[
V_{\text{terminal}} = \text{emf} - I \cdot r
\]
where \( I \) is the current and \( r \) is the internal resistance of the cell. As long as there is current flowing, the terminal voltage will be less than the emf.
2. **Load Conditions**: The terminal voltage also depends on the load connected to the cell. If the load draws a significant amount of current, the effect of internal resistance becomes more pronounced, leading to a larger difference between the emf and terminal voltage.
In summary, the terminal voltage is always less than the emf due to the voltage drop caused by the internal resistance of the cell when current flows.
The EMF (electromotive force) of a cell is the maximum potential difference between its terminals when no current is flowing, while the terminal voltage is the potential difference when the cell is under load, i.e., when current is flowing. The terminal voltage is always less than the EMF due to the internal resistance of the cell. As current flows, there is a voltage drop across this internal resistance, which reduces the terminal voltage. The greater the current, the larger the voltage drop, leading to a terminal voltage that is lower than the EMF.