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Combo Circuits & EMF

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# Combo Circuits & EMF - PowerPoint PPT Presentation

Combo Circuits & EMF. How much current flows from the battery in the circuit below?. 400 . 12V. 500 . 700 . EMF. Any device (battery) that transforms one type of energy into electric energy is called a source of electromotive force (emf)

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### Combo Circuits & EMF

400

12V

500

700

EMF
• Any device (battery) that transforms one type of energy into electric energy is called a source of electromotive force (emf)
• The potential difference between two terminals when no current is flowing is called the emf ()_
• When current flows the voltage across the terminal drops because charge must actually flow within the source and there is some internal resistance (r) in the source
The terminal voltage (Vab) of the source is thus the emf of the source minus the voltage lost to internal resistance
• Vab =  - Ir
• This is the voltage actually delivered by the source

a

b

Battery

What voltage is actually delivered by a 12V battery (with internal resistance of .1 ) when a 10 A current flows?
• In new batteries the r is usually very low, but as the battery ages, the internal resistance increases so it delivers a lower and lower voltage

For the circuit below with a 9.0V battery (internal resistance .50) A) How much current is drawn from the battery? B) What is the terminal voltage of the battery?

1

5

9V

2

3