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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. EMF vs. Terminal Voltage.
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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
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 theElectromotive Force or EMF ( ) • EMF is a misnomer because the battery does not deliver a force in Newtons • The potential difference ΔV=Vab , is measured across the terminals of a battery
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”
Battery Circuit • The terminal voltage is always smaller than the EMF
Resistors in Series • The current is the same through each resistor • Kirchhoff’s VoltageLaw states:
Series Circuit • Three lamps connected in a daisy-chain fashion can be considered as three resistors in series
Resistors in Parallel • The voltage across each resistor is the same as the battery voltage • Kirchhoff Current Law states:
Parallel Circuit • Three lamps connected across each other can be modeled as three resistors in parallel • For only 2 resistors in parallel, Req becomes:
