3/5 do now – on a new sheet An incandescent light bulb is supplied with a constant potential difference of 120 volts. as the filament of the bulb heats up, what happens to its resistance and its current? – show your reasoning Due: 20.1 notes Ω work: Castle learning 20.2 notes Unit test – 3/14 Questions from packets

Lesson 1: Circuit Connections Circuit Symbols and Circuit Diagrams Two Types of Connections Finish lab 15

Circuit Symbols Voltage sources Resistances Measurement Devices Other Elements Draw a schematic circuit with three light bulbs, wires and one battery.

Example: Three D-cells are placed in a battery pack to power a circuit containing three light bulbs Only use circuit symbols in your reference table to draw the circuits

Two types of connections These two examples illustrate the two common types of connections made in electric circuits. When two or more resistors are present in a circuit, they can be connected in series or in parallel.

Circuit Elements – Measuring Devices Measures: VOLTAGE Resistance: HIGH Connect to circuit: OUTSIDE Measures CURRENT Resistance: LOW Connect to circuit: INSIDE voltmeter ammeter

Meters in a circuit V A V A

Two types of circuits http://phet.colorado.edu/en/simulation/circuit-construction-kit-dc series parallel As the light bulbs are added, what happens to the current going to the battery As the light bulbs are added, what happens to the total resistance of the circuit? If one light bulb is taken out, what happens to the other light bulbs? As the light bulbs are added, what happens to the current going to the battery As the light bulbs are added, what happens to the total resistance of the circuit? If one light bulb is taken out, what happens to the other light bulbs?

For series circuits As more resistors are added the overall current within the circuit decreases. This decrease in current is consistent with the conclusion that the overall resistance increases. If one of three bulbs in a series circuit is unscrewed from its socket, then the other bulbs immediately go out.

For parallel circuits As the number of resistors increases, the overall current also increases. This increase in current is consistent with a decrease in overall resistance. Adding more resistors in a separate branch has the unexpected result of decreasing the overall resistance! If an individual bulb in a parallel branch is unscrewed from its socket, other bulbs are not effected.

Check Your Understanding 1. Observe the electrical wiring below. Indicate whether the connections are series or parallel connections. Explain each choice.                                                                                                              

2. Two electric circuits are diagrammed below 2. Two electric circuits are diagrammed below. For each circuit, indicate which two devices are connected in series and which two devices are connected in parallel. In series? ______________ In parallel? ______________ In series ________________