chapter18.1-18.4_updated

chapter18.1-18.4_updated - 2/4/2009 1 Direct Current...

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Unformatted text preview: 2/4/2009 1 Direct Current Circuits Direct Current (DC): Current goes only in one direction. I I I I I I The source that maintains the current in a closed circuit is called a source of emf Potential energy of charges circulating in circuits are increased by sources of emf Examples: batteries, generators, adapters, solar cells, etc SI units are Volts; symbol : Meaning: Work done by the emf per unit charge Same as electrical potential Q W 2/4/2009 2 Batteries: store chemical potential energy When connected to a circuit, chemical energy is converted to electrical energy The electrical energy is finally converted into other forms of energy (eg., into heat by resistors, light/heat by light bulb, etc) V All sources of emf have certain internal resistance r The terminal voltage is the voltage measured from the two terminals of the battery Terminal voltage in general is not the same as the emf of the battery Demo: Voltmeter readings (a) Before connecting the resistor (b) After connecting the resistor V V 2/4/2009 3 is equal to the terminal voltage When the current is zero Also called the open-circuit voltage R is called the load resistance The current depends on both the resistance external to the battery and the internal resistance V V Why the difference in terminal voltage? internal resistance A battery with an internal resistance r can be represented by an ideal battery in serial with a resistor r From the above diagram, R r V V R V r V ) ( R r I IR Ir 2/4/2009 4 Calculate the internal resistance of a battery (1) Current (2) (3) V 4 . 1 2 V 5 . 1 R V R R V I R R r R r V V V V I V r Ir V r r R V Battery A emf Internal resistance V 5 . 1 5 . r Battery B emf Internal resistance V 2 . 1 1 . r Which batter delivers a greater current when connected to a 1 external resistor? (1) Battery A (2) Battery B ) ( ); ( r R I r R I 2/4/2009 5 Battery A emf Internal resistance V 5 . 1 5 . r Battery B emf Internal resistance V 2 . 1 1 . r Which batter delivers a greater current when connected to a 12 external resistor?...
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This note was uploaded on 03/30/2009 for the course PHY 102 taught by Professor Luo during the Spring '08 term at SUNY Buffalo.

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chapter18.1-18.4_updated - 2/4/2009 1 Direct Current...

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