Have you ever wondered how a battery works or why devices need one to function? Two important terms related to batteries are EMF (Electromotive Force) and Potential Difference. While they sound similar but they are not the same. Let’s explore these concepts in simple terms and understand their differences.
What Is EMF in a Battery?
The electromotive force is not a force and we cannot measure it in newton (N). It is the total energy a battery can provide to push charges through a circuit. Think of EMF as the full “strength” or “power” of the battery when it’s brand new and not connected to any device.
For example, if you read “1.5V” on a battery, that’s its EMF. It’s the maximum voltage the battery can deliver.
What Is Potential Difference?
Potential Difference, on the other hand, is the actual voltage measured between the two terminals of the battery when it is connected to some external circuit. It shows how much energy is being used to keep the current flowing.
Why the potential difference of the battery is smaller than its EMF?
The potential difference of a battery is less than its EMF because of the internal resistance inside the battery.
When a battery is in use (i.e., connected to a circuit), some of the energy provided by the EMF is used to overcome this internal resistance. This energy loss appears as heat within the battery, leaving less energy available to push charges through the external circuit.
This is why the potential difference, measured across the battery’s terminals during use, is lower than the EMF, which represents the battery’s maximum energy when no current flows.
The formula of EMF and potential difference:
The relationship can be expressed as:
\( V = E – I \cdot r \)
Where:
- V: Potential difference across the battery terminals
- E: The EMF of the battery
- I: Current in the circuit
- r: Internal resistance of the battery
As the current (I) increases, the energy lost due to (I.r) becomes more significant, which further reduces the potential difference.
Why Are They Not the Same?
Here’s an easy way to understand it:
- EMF is like the total water in a tank, ready to flow.
- Potential Difference is the water flowing through the pipe.
When a device like a flashlight or toy car uses a battery, some energy is lost as heat due to the battery’s internal resistance. That’s why the potential difference is usually less than the EMF.
Examples to Clarify
- Fresh Battery: If you check a new battery with a multimeter, it will show the EMF (e.g., 1.5V).
- Battery in Use: When the battery is in a flashlight, the voltage measured across its terminals (potential difference) might be 1.3V because some energy is lost inside the battery.
The EMF is a “cause,” and the potential difference is its “effect.” What does this mean?
EMF is the energy that pushes charges to move in a circuit, like a pump starting water flow. The potential difference happens as a result of this movement when the charges use the energy in different parts of the circuit. In simple terms, EMF starts the flow (the cause), and the potential difference shows up because of it (the effect).
Why Is It Important to Know the Difference?
Understanding EMF and the potential difference helps in designing circuits and choosing the right batteries for your devices. It also explains why batteries lose efficiency over time.
