lect549 - I=V/R Ohm’s Law The current through a metal...

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Electric Currents

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The Electric Battery
Electric Cell

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Electric Current
When a continuous conducting path is connected between the terminals of a battery, we have an electric circuit .

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When such a circuit is formed, charge can flow through the wires of the circuit, from one terminal of the battery to the other. A flow of charge such as this is called as electric current . t Q I =
Units of Current 1 Ampere (A) = 1 C /1 s

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Conceptual Example: How to Connect a Battery. What’s wrong with each of circuits shown below?
Conventional Current

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When we speak of the current flowing in a circuit, we mean the direction positive charge would flow.
Important : Current is not a vector, it’s a scalar!!!!

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Important : In any single circuit, the current at any instant is the same at one point as at any other point!!! This follows from the conservation of electric charge.
Ohm’s Law: Resistance and Resistors I~V

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Definition of Resistance

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Unformatted text preview: I=V/R Ohm’s Law The current through a metal conductor is proportional to the applied voltage. Resistivity A L R ρ = Conceptual Example: Stretching Changes Resistance A wire of resistance R is stretched uniformly until it is twice its original length. What happens to its resistance? Effect of Temperature )) ( 1 ( T T T-+ = α ρ α – temperature coefficient of resistivity is positive for metals and negative for semiconductors. Superconductivity 1. When you stack three flashlight batteries in the same direction, you get a voltage of 3x1 ½ volts = 4 ½ volts. What voltage do you get if one of the batteries is turned to face in the opposite direction? 2. What is the difference between a bulb burning out and removing the bulb from its socket? 3. If the resistance connected to a battery is cut in half, what happens to the current through the battery?...
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This note was uploaded on 05/05/2009 for the course PHYSICS 1002 taught by Professor Borovitskaya,elena during the Spring '09 term at Temple.

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lect549 - I=V/R Ohm’s Law The current through a metal...

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