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

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SUMMARY

A battery's electromotive force (emf) and terminal voltage are distinct concepts. The emf represents the maximum energy supplied per coulomb of charge, while terminal voltage is affected by the internal resistance of the battery. When current flows, some emf is lost due to internal resistance, resulting in a lower terminal voltage. Both values are equal when no current flows, but during a short circuit, the terminal voltage drops to zero as all emf is consumed by internal resistance.

PREREQUISITES
  • Understanding of electromotive force (emf)
  • Knowledge of internal resistance in batteries
  • Familiarity with voltage concepts in electrical circuits
  • Basic principles of current flow in circuits
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  • Research the impact of internal resistance on battery performance
  • Learn about measuring terminal voltage in practical applications
  • Explore the effects of short-circuiting on battery behavior
  • Study the differences between ideal and real voltage sources
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Electrical engineers, battery technologists, students studying circuit theory, and anyone interested in understanding battery performance and behavior in circuits.

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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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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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thank you this is a great explanation
 

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