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Electric Current

Electric Current. Electric Current. The rate of flow of electric charges Unit of measure is coulombs per second, or amperes I – rate of flow (current) (amps) q – charge (coulomb) t –time (sec). Sample Problem. 10 Coulombs goes through a conductor in 5 seconds. What is the current?.

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Electric Current

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  1. Electric Current

  2. Electric Current • The rate of flow of electric charges • Unit of measure is coulombs per second, or amperes • I – rate of flow (current) (amps) • q – charge (coulomb) • t –time (sec)

  3. Sample Problem • 10 Coulombs goes through a conductor in 5 seconds. What is the current?

  4. Conductivity • Ability to conduct a current • Metals – Good • Liquids – Vary • Solutions (Electrolytes) – Good • Gases – Good

  5. Conditions Necessary for a Current • A difference in potential is required to maintain a flow of charge between 2 points in a conductor Flow of positive charges* - + Flow of electrons V

  6. Motion Inside a Conductor • Electrons are accelerated by an electrical field • Collisions with fixed particles of the conductor • Create heat • “Plinko”

  7. Resistance • The opposition to the electron moving through a conductor is called Resistance (R) • The unit of resistance is OHM (Ω) R – Resistance (OHM (Ω)) V – Potential Difference (Volts, V) I – Current (Amps, A)

  8. Sample Problem • When a conductor has a potential difference of 110 volts placed across it, the current through it is 0.50 ampere. What is the resistance of the conductor? • How many electrons pass through this coil per second?

  9. Factors that Affect Resistance • Length of Wire • Directly proportional to its length (length up, resistance up) • Cross-Sectional Area • Inverse relationship (thicker the wire, less resistance) • Temperature • Resistance INCREASES when Temperature INCREASES • Type of Material (Resistivity) • Insulator vs Conductors

  10. Resistivity of Materials • How well a substance resists carrying a current is known as resistivity (ρ). • The unit is ohm·meter (Ω·m) • Reference Table

  11. Resistivity • R - Resistance • ρ – resistivity (ohm·meter) • L – length of wire (meter) • A – Cross-sectional area (m2)

  12. Sample Problem • Calculate the resistance at 200 C of an aluminum wire that is 0.200 meter long and has a cross-sectional area 1.00x10-3 m2 .

  13. Electric Circuits and Ohm’s Law • Circuit means “closed path” • Typically circuits have a source of potential difference, a resistance and wires

  14. Interpreting a Completed Circuit • Current travels from (+) to (-) • Electrons travel opposite

  15. Graphs of Ohm’s Law

  16. SHOW WORK

  17. Electrical Power • Power is the rate at which work is being done • Derivations P – Power (Watts) V – Potential Difference (Volts, V) I - Current (Amperes, Amps)

  18. Sample Problem • A lamp designed for a 120 Volt circuit is labeled 60 watts. What is the operating resistance of the lamp?

  19. Electrical Work and Energy • The work required to maintain a current is equal to power x time

  20. Sample • How much electrical energy is supplied to a 60 watt bulb in 10 seconds? • How much energy is produced by a 50 volt source that generates a current of 5.0 amperes for 2.0 minutes

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