Are a Battery's EMF and Terminal Voltage the Same?

In summary, a battery's emf is the maximum energy supplied to each coulomb of charge passing through the battery, while its terminal voltage is the actual voltage available at the battery's terminals. This is because batteries have internal resistance which causes some of the emf to be lost as the current flows. When there is no current flowing, the terminal voltage and emf are the same. However, in a short circuit, all of the emf is lost and there is zero terminal voltage.
  • #1
jimbo71
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How are a battery's emf and its terminal voltage different? Can they ever be the same value?
 
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  • #2
A battery's emf is the maximum energy supplied to each coulomb of charge passing through the battery. A battery (and other sources for that matter) have internal resistance. When a current flows, some of the supply's emf is 'lost' as V = Ir where r is the internal resistance. These 'lost' volts aren't available to the terminals, therefore terminal voltage is 'lost' volts subtracted from the emf. Terminal voltage and emf have the same value when no current flows in a circuit as no volts will be 'lost'. On the other hand, when a source is short-circuited there is no external resistance (load) so all the emf is dropped across the internal resistance, and thus the entire emf becomes 'lost' volts and there is zero terminal voltage.
 
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  • #3
thank you this is a great explanation
 

1. What is EMF?

EMF stands for electromotive force, which is the potential difference between two points in an electrical circuit. It is essentially the driving force that causes current to flow.

2. How is EMF related to terminal voltage?

In an ideal circuit, the EMF is equal to the terminal voltage, which is the voltage measured at the terminals of a battery or power source. However, in real circuits, there may be a difference between the EMF and terminal voltage due to internal resistance.

3. What factors affect EMF and terminal voltage?

The main factors that affect EMF and terminal voltage include the type and design of the power source, the materials used, and the presence of any external resistors or loads in the circuit.

4. How can EMF and terminal voltage be calculated?

EMF can be calculated using the equation EMF = I(R + r), where I is the current, R is the external resistance, and r is the internal resistance. Terminal voltage can be calculated using the equation V = EMF - Ir, where V is the terminal voltage and I is the current.

5. What are some applications of EMF and terminal voltage?

EMF and terminal voltage are important concepts in understanding and designing electrical circuits. They are also crucial in the development and use of batteries, generators, and other electrical devices. Additionally, they play a role in areas such as power distribution and renewable energy systems.

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