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Concept Summary Batesville High School Physics

Electric Current. Concept Summary Batesville High School Physics. Potential Difference. Charges can “lose” potential energy by moving from a location at high potential (voltage) to a location at low potential.

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Concept Summary Batesville High School Physics

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  1. Electric Current Concept Summary Batesville High School Physics

  2. 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.

  3. 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, soCurrent = or I = q/t Charge time

  4. Measuring Current • If 1 Coulomb of charge (6.25 x 1018 electrons) passes a point each second, the current is 1 Ampere. • So, 1 Ampere = 1 Coulomb/sec

  5. 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.

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

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

  8. 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

  9. 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

  10. Ohms’ Law • In symbols: • V = IR V I R

  11. 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.

  12. 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.

  13. 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.

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

  15. 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.

  16. Electric Power • Power = energy/time = current x voltage • P = IV = I2R • 1 Watt = (1 Amp)(1 Volt) • 1 kilowatt = 1000 Watts • A kilowatt-hour is a unit of energy

  17. The End

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