lecture 5

lecture 5 - Chapter 20 Electric Circuits Outline Section...

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Electric Circuits Chapter 20
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Outline Section 20.01: Electromotive Force and Current Section 20.02: Ohm’s Law Section 20.03: Resistance and Resistivity Section 20.04: Electric Power Section 20.05: Alternating Current Section 20.06: Series Wiring Section 20.07: Parallel Wiring Section 20.08: Series-Parallel Wring Section 20.09: Internal Resistance Section 20.10: Kirchhoff’s Rules
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20.1 – Electromotive Force Every electronic device depends on circuits. Electrical energy is transferred from a power source, such as a battery, to a device, say a light bulb. Battery Light bulb + - Light A diagram of this circuit would look like the following: + - Battery symbol Inside a battery, a chemical reaction separates positive and negative charges, creating a potential difference. This potential difference is equivalent to the battery’s voltage, or emf ( ε ) (electromotive force). This is not really a “force” but a potential. Conducting wires Because of the emf of the battery, an electric field is produced within and parallel to the wires. This creates a force on the charges in the wire and moves them around the circuit. This flow of charge in a conductor is called electrical current ( I ).
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A measure of the current is how much charge passes a certain point in a given time: t q I = Units? [ ] [ ] A Ampere s C time Charge = = = Electrical Current If the current only moves in one direction, like with batteries, it’s called Direct Current (DC). If the current moves in both directions, like in your house, it’s called Alternating Current (AC). Electric current is due to the flow of moving electrons , but we will use the positive conventional current in the circuit diagrams. Battery Light bulb + - I I I e So I shows the direction of “positive” charge flow from high potential to low potential.
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20.2 – Ohm’s Law The flow of electric current is very analogous to the flow of water through a pipe: The battery pushing the current acts like the water pump pushing the water. The voltage of the battery is analogous to the pump pressure – the higher the pump
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lecture 5 - Chapter 20 Electric Circuits Outline Section...

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