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Reading Quiz A light bulb is connected to a battery so that current flows through the bulb, which gives off light. Choose the correct statement: The amount of current going into the bulb equals the current leaving the bulb. The amount of current entering the bulb is greater than the amount of current leaving the bulb. The bulb is converting electric charge into light.

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Physics Help Center Room 237 Physics Building: 8am to 5:30pm Ask for help from graduate students on homework and exams Can enter solutions on the computers in the room to check your solution. NEXT EXAM Wednesday April to 9pm Chapters 10,11,12,13,14,15

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Summary of electric circuits: 1.The amount of current is the same at every place in a series circuit; I=q/t. 2.The power provided by the battery (P=I V) is exactly equal to the power dissipated in the resistors (P=I 2 R). 3.Ohm’s Law applies to resistors: V=IR 4.Series circuit: effective R = R 1 + R 2 + R 3 5.Parallel circuit: effective R is

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Fig. 13.3

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Fig. 13.1

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Fig. 13.2

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Fig. 13.4

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Summary 2

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Ohm’s Law applies to resistors: V=IR R EMF volts Battery increases energy of charges ( PE); voltage on battery is called “EMF”. This amount of energy is expended in the resistor. For a given battery (V) and resistor (R), the current is given by Ohm’s Law: V=IR The unit of resistance is an Ohm. I V

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Fig. 13.6

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Fig. 13.7

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Fig. 13.5

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Lecture Quiz 26 - Question 1: A simple battery does which of the following: A. It creates charges. B. It does work on charges. C. It creates energy.

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EMF volts V R1R1 R2R2 R3R3 Series Resistance EMF= V 1 + V 2 + V 3 OR V = IR 1 + IR 2 + IR 3 = I(R 1 + R 2 + R 3 ) = I R series Where R series = R 1 + R 2 + R 3 Is the voltage drop the same across all three resistors? Is the current the same through all three resistors?

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Fig. 13.9

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Exercise 9 What is the total resistance of this circuit? 1.) 66 ohms 2.) 60 ohms 3.) 54 ohms 4.) 25 ohms 5.) 15 ohms

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Exercise 9 What is the current that flows in this circuit? 1.)10 amps 2.) 1 amp 3.) 0.1 amp 4.) 0.3 amp 5.) 0.03 amps

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Fig

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Parallel Resistors V Effective resistance Where V = I R effective EMF volts 123 How much current flows through the three resistors? Is the voltage drop the same for all three resistors?

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Exercise 12 What is the total resistance of this circuit? 1.) 72 ohms 2.) 24 ohms 3.) 12 ohms 4.) 8 ohms 5.) 2 ohms

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What is the current that flows in this circuit at point A? 1.)288 amps 2.) 1.5 amp 3.) 0.1 amp 4.) 0.5 amp 5.) 0.03 amps A.A.

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What is the current that flows in this circuit at point B? 1.)288 amps 2.) 1.5 amp 3.) 0.1 amp 4.) 0.5 amp 5.) 0.03 amps B.B.

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By placing all electric items in parallel they receive the same voltage By placing electrical items in series they receive the same current

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A volt meter has a high resistance so take very little current

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Fig An Amp meter has very little resistance so take very little voltage

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Summary of electric circuits: 1.The amount of current is the same at every place in a circuit; I=q/t. 2.The power provided by the battery (P=I V) is exactly equal to the power dissipated in the resistors (P=I 2 R). 3.Ohm’s Law applies to resistors: V=IR 4.Series circuit: effective R = R 1 + R 2 + R 3 5.Parallel circuit: effective R is

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Question 14

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The power provided by the battery (P=I V) is exactly equal to the power dissipated in the resistors (P=I 2 R). Power P= work/time Power= PE/t =q V/t =I V =IV For an “ohmic” resistor, V=IR, so P = I 2 R

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Lecture Quiz #26 Question 2 Consider a standard flashlight which is turned on. A. The batteries create electrons, which get used up in the light bulb. B. Energy is created in the batteries, which is destroyed in the light bulb. C. The power used up by the light bulb originates in the batteries. D. The light bulb converts electrons into light.

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Lecture Quiz: Question 3 How much current I runs through this circuit: A Amps B A C A D A E A 3 V 4

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Lecture Quiz: Question 4 For three resistors in parallel, choose the correct statement: EMF volts 123 A. The current and the voltage across all three are the same. B. The voltage drop and the power dissipated across all three are the same. C. The energy given up per electron is the same for all three. D. The current through one resistor is the same as the current through the battery.

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The amount of current is the same at every place in a (single- loop) circuit; I=q/t. Battery Light Bulb What does the battery do? Where does the light energy come from? Why do batteries burn out? I I I I

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