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Current Electricity

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11.1 Electric Current

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Circuit – continuous conducting path between terminals of a battery (or other source of EMF) Electric Current – flow of charge (electrons) I – current (amperes) Q – charge (coulomb) T – time

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11.1 Electric Current Ampere (for Andre’ Ampere) Usually called an amp Open Circuit – break in the circuit, no current flow

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11.1 Electric Current Short Circuit – when the load is bypassed Current increase Ground – allows for a continuous path for charge flow

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11.1 Electric Current For historical reasons, current is defined as being in the direction that positive charge flows

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11.3 Resistance and Ohm’s Law

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George Simon Ohm The actual values depend on the resistance of the conductor Called Ohm’s Law R – resistance measured in Ohms ( )

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11.3 Resistance and Ohm’s Law Resistor – anything that uses electric energy Resistor – device used to control current The symbol for a resistor is

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11.3 Resistance and Ohm’s Law The resistance value of a resistor is indicated by the colored bands on the resistor

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11.3 Resistance and Ohm’s Law Misconceptions 1.Cells (batteries) do not put out a constant current. They maintain a constant potential difference. 2.Current passes through a wire and depends on the resistance of the wire. Voltage is across the ends of the wire. 3.Current is not a vector, it is always parallel to the conductor. The direction is from + to -.

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11.3 Resistance and Ohm’s Law Misconceptions 4. Current or charge do not increase or decrease. The amount of charge in one end of the wire comes out of the other end.

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11.5 Superconductors

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An element or compound that conducts electricity without resistance Become insulators above a critical temperature Uses MagLev Trains

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11.6 Electrical Energy and Power

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The rate of energy flow for an electric circuit That is more commonly written as Combining with Ohm’s Law it can also be written

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11.6 Electrical Energy and Power The power company charges by the kilowatt- hour (kWh) Just a cool picture

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11.6 Electrical Energy and Power Household circuits – wires will heat up as current increases In a 20A household circuit In a 15A household circuit Circuits are typically designed to run at 80% of the rated power output Different circuits have different gauge wires (diameter)

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11.6 Electrical Energy and Power Circuit Breakers and Fuses Break the circuit

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11.7 Sources of EMF

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EMF – electromotive force – the potential difference between the terminals of a source when no current flows to an external circuit ( )

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11.7 Sources of EMF A battery will have an internal resistance (r) So there is a potential drop due to the current that travels through the cell So the actual potential across the terminals of a cell will be This is called the terminal voltage

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11.8 Resistors in Series

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11.7 Sources of EMF When resistors are place in a single pathway They are said to be in series A schematic would look like this

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11.7 Sources of EMF The current in a series circuit is the same throughout the circuit The potential across the source of EMF is equal to the sum of the potential drops across the resistors

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11.7 Sources of EMF Since potential can be defined as We can rewrite the equation for potential as

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11.9 Resistors in Parallel

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When resistors are place in a multiple pathways They are said to be in parallel A schematic would look like this

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11.9 Resistors in Parallel The potential difference in a parallel circuit is the same throughout the circuit The current through the source of EMF is equal to the sum of the current through the resistors

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11.9 Resistors in Parallel Since current can be defined as We can rewrite the equation for potential as

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11.9 Resistors in Parallel Circuits that contain both series and parallel components need to be solved in pieces This circuit contains 20 resistors in series 25 resistors and load series to each other and parallel to the 40 resistor

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