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Published byJohana Neville Modified over 2 years ago

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Unit 3 Day 5: EMF & Terminal Voltage, & DC Resistor Circuits Electromotive Force (EMF) Terminal Voltage Internal Resistance Series, Parallel, and Series- Parallel Resistor Networks Kirchhoff’s Current & Voltage Laws

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EMF vs. Terminal Voltage For current to flow through a circuit, we need a device to supply the electrical energy, ie: a battery A device that supplies electrical energy to a circuit is called the source of what is referred to as the Electromotive Force or EMF ( ) EMF is a misnomer because the battery does not deliver a force in Newtons The potential difference ΔV=V ab, is measured across the terminals of a battery

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Internal Resistance The battery is not a constant source of current because of internal losses within the battery The chemical reaction that produces the electrical energy also produces heat, and may be modeled as a resistor internal to the battery. This is called the internal resistance “r”

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Battery Circuit The terminal voltage is always smaller than the EMF

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Resistors in Series The current is the same through each resistor Kirchhoff’s Voltage Law states:

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Series Circuit Three lamps connected in a daisy-chain fashion can be considered as three resistors in series

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Resistors in Parallel The voltage across each resistor is the same as the battery voltage Kirchhoff Current Law states:

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Parallel Circuit Three lamps connected across each other can be modeled as three resistors in parallel For only 2 resistors in parallel, R eq becomes:

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Series-Parallel Resistor Networks

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