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Warm Up 1. What color absorbs ALL colors of the visible light spectrum? 2. What color reflects ALL colors of the visible light spectrum? 3. Where does light travel fastest? 4. Where does light travel slowest? 5. We see different colors because objects reflect different _______________ of light. a) Amplitudes b) Wavelengths c) Speeds

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Series and Parallel Circuits

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is the measure of how difficult it is for charges to flow through a material unit: is the amount of charge that passes by a point in a second unit: -the difference in electrical potential energy between 2 places in a circuit; it is the energy that pushes charges through a circuit unit: resistance Ohm (Ω) current Ampere, amp, A voltage volt, V

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Objectives Name the three essential parts of a circuit. Compare series circuits with parallel circuits. Explain how fuses and circuit breakers protect your home against short circuits and circuit overloads. Compare motors and generators

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Electric Circuits An electric circuit is a complete, closed path through which electric charges flow. All circuits have three basic parts: Energy source Wires Load

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Energy source examples: Battery Generator power plant (coal, nuclear, gas) hydroelectric plant Loads change electrical energy to other forms of energy Examples: lightbulb, television, toaster Wires are made from conductive materials (i.e., copper)

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A switch is used to open and close a circuit. When the switch is open, electrical current CANNOT flow

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Brain Pop: Electric Circuits

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Circuits Can either be series or parallel or a combination of the two.

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Series Current only takes one path for electrons Current flows through every part of the circuit

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Lights in a Series

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Series If you add a resistor (like another light): Total resistance goes UP since all the current has must go through each resistor.

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Adding Resistors to Series: Current in the circuit will go DOWN (lights will dim) If you remove a light bulb or one burns out—all go out!

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Resistance in Series Add up all resistors to get total resistance Total resistance will go up because all of the current must go through each resistor.

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Calculating Resistance Example: If the resistances of loads R1, R2, and R3 are 10Ω, 20Ω & 30Ω respectively, what is the total resistance in the circuit?

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Current in Series Current is the same at all points Use Ohm’s Law to find current using resistance and voltage

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Calculating Current Example: If the resistances of loads R1, R2, and R3 are 10Ω, 20Ω & 30Ω respectively, and the voltage source is 6 V, what is the current through the circuit?

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Voltage in Series Voltage is reduced by each resistance – voltage drop

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Calculating Voltage Example Using the current that you calculated in the previous problem, what is the voltage difference (drop) across each resistor?

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Sample Problem #1 Draw a series circuit with two 1.5 V batteries, 3 resistors, and a current of 0.5 A. 1. What is the total voltage of the circuit? 2. What is the resistance of each resistor? 3. What is the voltage drop across each resistor? Label it on your circuit.

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Parallel Circuits Have at least one point where current divides More than one path for current to flow Paths are also known as branches

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Lights in Parallel

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Parallel: If you add a resistor: Total resistance goes down Total current goes up when you add another path

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Removing a Light Bulb If you remove a light bulb or one burns out, the others stay on because the circuit is still closed.

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Current in Parallel Current flows into a branching point, the same total current must flow out again Current depends on resistance in each branch

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Calculating Total Resistance in a Parallel Circuit Kirchoff’s Law of Currents states that the sum of the currents in must equal the sum of the currents out. The formula for calculating total Resistance, R T :

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Current in Parallel Calculate current in each branch based on resistance in each branch by using Ohm’s Law

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Calculating Current Example: If the resistances of loads R1, R2, and R3 are 10Ω, 20Ω & 30Ω respectively, what is the total resistance in the circuit?

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Voltage in Parallel Voltage is the same across each branch – because each branch is on the same wire

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Calculating Voltage Example: If the voltage source is 6 V, what is the voltage difference (drop) across each resistor?

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Practice problem #2 Draw a parallel circuit with a 6 ohm & a 18 ohm resistor (one on each branch) and a 12 V battery. 1. What is the voltage through each resistor? 2. What is the current flowing through each branch?

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Toll Road—Circuit Analogy

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Toll Booth Explanation Adding toll booths in series increases resistance and slows the current flow. Adding toll booths in parallel lowers resistance and increases the current flow.

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Batteries in Series and Parallel:

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In series—The voltage is increased. In parallel—No change in voltage; these batteries will last longer!

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One More FINAL Thing: Two Types of Current: DC—Direct Current— produced by solar cells and chemical cells (batteries) Current only flows in one direction.

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2 nd type of current: AC—Alternating Current Current flows back and forth (alternates) Found in homes Generators produce AC current

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Too many loads or too much voltage can be dangerous fuse -thin strip of metal that melts and opens circuit circuit breaker – sometimes a piece of metal that bends, thus opening the circuit

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Generator – converts mechanical to electrical energy Motor – converts electrical to mechanical energy

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When Andre plugs his stereo into the same outlet as the television and lamp, all three won’t work. What is the most likely hypothesis for what happened? A The circuit was overloaded, and the circuit breaker opened. BThe circuit was complete, and the circuit breaker closed. COnly the stereo operates on alternating current. DThe stereo’s electrical cord was faulty.

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Suki can have all five appliances in her kitchen on at the same time, or she can have each appliance on one at a time. How are the appliances in Suki’s kitchen wired? Ain a single loop Bin a direct current circuit Cin a parallel circuit Din a series circuit

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