Electromotive Force: Terminal Voltage

Electromotive Force: Terminal Voltage

By Rachel Wampler

• Voltage produced that could drive a current through a circuit ​

• εmf = electromotive force

• ​Not really a "force"

Electromotive Force

Internal Resistance

• Batteries and generators have resistance

  • In batteries resistance is due to chemicals

  • In generators resistance is due to wires and other components​

• Internal resistance is connected in series with the equivalent resistance of the circuit​

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Terminal Voltage

Multiple Choice

A string of Christmas lights are connected in series with a 3.0 V battery. Each light has a resistance of 10 Ω. The terminal voltage is measured as 2.0 V.

What is the internal resistance of the battery?

• 66.7 Ω

• 0.015 Ω

• 100 Ω

• 0.01 Ω

Multiple Choice

A battery has an internal resistance of 0.02 Ω and an emf of 1.5 V. If the battery is connected with five 15 Ω light builbs connected in parallel, what is the terminal voltage of the battery?

• 0.497 V

• 1.49 V

• 3.02 V

• 1.50 V

Multiple εmf sources

• If batteries are connected in series, their εmf's add, but so do their internal resistances.

• If batteries are connected in parallel their εmf​'s stay the same, but their currents add and the combined internal resistance is less.

• Think of this as resisters in series, parallel, or both; depending on the situation. ​