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Concept Summary Batesville High School Physics

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Potential Difference Charges can “lose” potential energy by moving from a location at high potential (voltage) to a location at low potential. Charges will continue to move as long as the potential difference (voltage) is maintained.

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Current A sustained flow of electric charge past a point is called an electric current. Specifically, electric current is the rate that electric charge passes a point, so Current = or I = q/t Charge time

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Measuring Current If 1 Coulomb of charge (6.25 x 10 18 electrons) passes a point each second, the current is 1 Ampere. So, 1 Ampere = 1 Coulomb/sec

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Voltage Source A battery or electrical outlet is a source of electric potential or voltage - not charge. The electrons that move in a conductor are supplied by the conductor - not the voltage source. The net charge on a current-carrying conductor is zero.

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Electromotive Force An old-fashioned term for electric potential or voltage is “electromotive force” or “emf”.

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Electrical Resistance Most materials offer some resistance to the flow of electric charges through them. This is called electrical resistance.

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Resistance Resistance of a conductor depends on: Material - Gold is best Length - longer conductors have more resistance. Cross section - thick wires have less resistance than thin wires Temperature - higher temperature means more resistance for most conductors

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Ohm’s Law For many conductors, current depends on: Voltage - more voltage, more current Current is proportional to voltage Resistance - more resistance, less current Current is inversely proportional to resistance

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Ohms’ Law In symbols: V = IR V IR

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Direct Current If the voltage is maintained between two points in a circuit, charge will flow in one direction - from high to low potential. This is called direct current (DC) Battery-powered circuits are dc circuits.

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Alternating Current If the high & low voltage terminals switch locations periodically, the current will flow “back and forth” in the circuit. This is called alternating current (AC). Circuits powered by electrical outlets are AC circuits.

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AC in the US In the US, current changes direction 120 times per second, for a frequency of 60 cycles per second or 60 Hertz. Normal outlet voltage in the US is 110- 120 volts, although some large household appliances run on 220-240 volts.

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Converting AC to DC AC is converted to DC using devices called diodes, which allow charges to move in only 1 direction.

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Speed of Electrons Electrons in a circuit do not move quickly - they actually “drift” at about 1 mm/s. It is the electric field that moves quickly - at about the speed of light - through the circuit and carries the energy.

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Electric Power Power = energy/time = current x voltage P = IV = I 2 R 1 Watt = (1 Amp)(1 Volt) 1 kilowatt = 1000 Watts A kilowatt-hour is a unit of energy

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The End

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Electric Current Electrical current is the flow of electrons. Unlike static electricity, charges are in motion. Two types of Current I. Direct current.

Electric Current Electrical current is the flow of electrons. Unlike static electricity, charges are in motion. Two types of Current I. Direct current.

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