Electric Circuits

Objectives Distinguish between series and parallel connections Calculate the current, voltage, and equivalent resistance for devices connected in series and parallel Construct a voltage divider Describe the features of a multi-meter and explain how to use it in a circuit

Electric Circuit Components Capacitor Stores charge Creates a potential difference Source of energy Resistor “Opposes” current (charge flow) “Uses” potential difference Dissipates energy

Electric Circuits Electric current requires two conditions A “closed” circuit, or complete path for charges to flow A potential difference, or voltage source (usually a cell or battery)

Electric Circuits Two types of electric circuits Series (only one current path) Parallel (more than one current path, i.e. “branches”)

Equivalent Resistance Series resistors Resistors in series add together

Current The current through a circuit component is equal to the voltage divided by the resistance Textbook, Pg. 533

Voltage The voltage “drop” or potential difference across a circuit component equals the product of the current and the resistance Textbook, Pg. 534

Voltage Divider Series circuit used to produce a voltage source of desired magnitude from a higher-voltage battery Textbook, Pg. 535

Practice Problems Textbook, Page 534 #1 – 5 Textbook, Page 536 – 537 (Examples) Textbook, Page 537 #6 – 9

Equivalent Resistance Parallel resistors Resistors in parallel add together as the reciprocals Hint: Remember to invert the sum to find Req Textbook, Pg. 539

Kirchoff’s Laws Voltage Current Conservation of energy Conservation of charge

Conservation of Energy The sum of potential “drops” or voltages in a circuit equals the source In a series circuit, all the voltages add up to equal the source In a parallel circuit, the voltage applied to each branch is equal to the source

Conservation of Charge The sum of all currents in a circuit is equal to the current leaving the source In a series circuit, the current is the same at every point In a parallel circuit, the sum of all currents entering any junction is the same as the sum of all currents leaving the junction

Series-Parallel Circuit What is the voltage drop across each resistor and the current flowing through them?

Practice Problems Textbook, Page 540 #10 – 12 Textbook, Page 547 #13

Measurements Voltmeter Ammeter Ohm-meter Multimeter Measures potential difference (volts) DVM (digital voltmeter) Ammeter Measures current (amps) Galvanometer (very sensitive ammeter) Ohm-meter Measures resistance (ohms) Multimeter Measures all three

Measurements Voltmeter Ammeter Ohm-meter Parallel Series Disconnect power Isolate resistor from circuit Textbook, Pg. 547