1 Answer
The electromotive force (emf) of a source is typically greater than the terminal potential difference (also called the terminal voltage) when there is a current flowing through the circuit.
Here's why:
When current flows through a source, some energy is lost as heat due to the internal resistance of the source. This loss reduces the voltage that appears at the terminals, so the terminal voltage is lower than the emf.
To sum it up:
For example, if you have a battery with an emf of 12V, and there's a current of 2A flowing, and the internal resistance is 1Ω, the terminal voltage will be less than 12V. It can be calculated as:
\[
V_{\text{terminal}} = \text{emf} - I \times r_{\text{internal}}
\]
\[
V_{\text{terminal}} = 12V - (2A \times 1Ω) = 10V
\]
So in this case, the terminal voltage is 10V, which is less than the emf of 12V.
Here's why:
- Emf (Electromotive Force): This is the potential difference across the terminals of the source (like a battery or a generator) when no current is flowing. It's the maximum potential difference the source can provide. It represents the energy supplied per charge by the source.
- Terminal Potential Difference (Terminal Voltage): This is the actual potential difference across the terminals of the source when the current is flowing in the circuit. This value can be less than the emf, due to the internal resistance of the source.
When current flows through a source, some energy is lost as heat due to the internal resistance of the source. This loss reduces the voltage that appears at the terminals, so the terminal voltage is lower than the emf.
To sum it up:
- Emf > Terminal Voltage when there is current, because of energy lost in the internal resistance.
- Emf = Terminal Voltage when no current is flowing (open circuit condition).
For example, if you have a battery with an emf of 12V, and there's a current of 2A flowing, and the internal resistance is 1Ω, the terminal voltage will be less than 12V. It can be calculated as:
\[
V_{\text{terminal}} = \text{emf} - I \times r_{\text{internal}}
\]
\[
V_{\text{terminal}} = 12V - (2A \times 1Ω) = 10V
\]
So in this case, the terminal voltage is 10V, which is less than the emf of 12V.