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Chapter 19: Electric Charges and Currents 19-3: The Flow of Electricity.

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Presentation on theme: "Chapter 19: Electric Charges and Currents 19-3: The Flow of Electricity."— Presentation transcript:

1 Chapter 19: Electric Charges and Currents 19-3: The Flow of Electricity

2 Making Electric Charges Move You must do work to move a charged particle against an electric field Unit of Charge: Unit of Charge: Coulomb (C) Electric Potential Difference (Voltage): Electric Potential Difference (Voltage): work required per coulomb of charge between 2 points Units: Units: Volt (V)

3 Battery Produces electricity by converting chemical energy into electrical energy Made up of electrochemical cells which are made from materials called electrodes and electrolyte Electric cells can be dry (paste-like) or wet (liquid) cells

4 Thermocouples Produces electrical energy from thermal energy Releases electric charges as a result of temperature differences Used in thermometers in cars to show engine temp. Engine gets warmer, increases flow of charge, moving charge operate gauge (also in ovens and gas furnaces)

5 Photocells When light with a certain amount of energy shines on a metal surface, electrons are emitted from the surface, electron routed through a wire to create a constant flow of electric charge

6 Electric Current Circuit:Circuit: complete path through which electric charge can flow Current ( I ):Current ( I ): amount of charge that passes a given point at a given time Unit of current: Unit of current: Ampere (A) **Potential Difference is required to produce an electric current**

7 Resistance Resistance (R):Resistance (R): opposition of the flow of electric charge Unit: Unit: Ohm (Ω) - Different wires have different resistances - All devices have some resistance - Depends somewhat on temperature: Resistance increases with temperature

8 Ohms Law The current in a wire ( I ) is equal to the voltage (V) divided by the resistance (R) Current = Voltage I = V Resistance R Amperes = Volts Ohms

9 Calculating Resistance In a Series circuit, total resistance is calculated by the equation: R = R 1 + R 2 + R 3 … In a Parallel circuit, total resistance is calculated by the equation:

10 Series and Parallel Circuits Series Circuit Parallel Circuit

11 Current Direct Current (DC):Direct Current (DC): current flow in the same direction (dry cells and batteries) Alternating Current (AC):Alternating Current (AC): amount of current changes in time and reverses direction regularly Current in your home changes direction 120 times every second

12 Calculations with Current Electricity 1. There is a 22-ohm resistance in the heating element of a coffee pot. It is plugged into a 110 Volt circuit. How much current passes? R= 22Ω I = V V = 110V R I =? I = 110 V 22 Ω I = 5 A

13 Calculations with Current Electricity 2. Three lamps with 40,60, and 80 ohms of resistance are connected in parallel to a 120 volt circuit. a) What current flows through each lamp? b) What is the total resistance of the 3 lamps? c) What is the total current used by the 3 lamps?Given: V = 120 V R 1 =40 ΩR 2 =60 ΩR 3 =80 Ω

14 a) What current flows through each lamp? Lamp 1: I = V/R I = 120V/40 Ω = 3.0 A Lamp 2: I = V/R I = 120V/60 Ω = 2.0A Lamp 3: I = V/R I = 120V/80 Ω = 1.5 A

15 b) What is the total resistance of the 3 lamps? Given: R 1 =40 Ω R 2 =60 ΩR 3 =80 Ω Since the circuit is in parallel, we use the equation: 1/R 1 +1/R 2 +1/R 3 = 1/40Ω + 1/60Ω +1/80Ω = 0.054Ω Then divide: 1/0.054Ω = 18.5Ω Total resistance = 18.5Ω

16 c) What is the total current used by the 3 lamps? Given: V = 120 V R T = 18.5Ω I = V/R T I = 120V/18.5Ω I = 6.5 A


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