1. 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

2. 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

3. 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”

4. Battery Circuit The terminal voltage is always smaller than the EMF

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

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

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

8. 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:

9. Series-Parallel Resistor Networks