Electromotive force (EMF) is the voltage generated by a source (like a battery) when no current is flowing, while voltage (or potential difference) is the electrical potential difference between two points in a circuit, whether current is flowing or not.
Breaking Down the Concepts
To understand the difference more clearly, consider these points:
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Electromotive Force (EMF):
- EMF is the cause of potential difference, arising from a device converting other forms of energy (chemical, mechanical, etc.) into electrical energy. Think of it as the 'push' that starts the current.
- It represents the maximum potential difference a source can provide.
- Measured in volts (V).
- It exists even when there's no current flowing in the circuit (open circuit).
- Example: The EMF of a battery is the potential difference across its terminals when no load is connected.
-
Voltage (Potential Difference):
- Voltage is the effect of the EMF; it's the potential difference that causes current to flow.
- It represents the potential difference between two points in a circuit.
- Measured in volts (V).
- It can exist even without an EMF source directly connected between those two points (e.g., due to the potential drop across a resistor).
- Example: The voltage drop across a resistor when current flows through it.
EMF vs. Voltage in a Battery
Let's consider a battery to further illustrate the difference:
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The EMF of the battery is the potential difference between its terminals when no current is flowing (i.e., when the circuit is open). It's the battery's inherent ability to generate electrical potential.
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The Voltage across the battery terminals will be less than the EMF when current is flowing due to the battery's internal resistance. The voltage is what's actually delivered to the circuit.
Summary Table
| Feature | Electromotive Force (EMF) | Voltage (Potential Difference) |
|---|---|---|
| Nature | Source of electrical potential | Difference in electrical potential between two points |
| Current Flow | Exists even with no current flow (open circuit) | Typically associated with current flow (but can exist statically) |
| Cause/Effect | Cause | Effect |
| Maximum Value | Represents the maximum possible potential | Can be less than the EMF due to internal resistance/voltage drops |
| Source | Battery, generator, etc. | Across a component, or between any two points in a circuit |
In essence, EMF is the ideal voltage a source can provide, while voltage is the actual potential difference measured between two points in a circuit, considering any losses.
