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Current Electricity

Current Electricity. 11.1 Electric Current. Circuit – continuous conducting path between terminals of a battery (or other source of EMF) Electric Current – flow of charge (electrons) I – current (amperes) Q – charge (coulomb) T – time. 11.1 Electric Current. Ampere (for Andre’ Ampere)

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Current Electricity

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  1. Current Electricity

  2. 11.1 Electric Current

  3. Circuit – continuous conducting path between terminals of a battery (or other source of EMF) Electric Current – flow of charge (electrons) I – current (amperes) Q – charge (coulomb) T – time 11.1 Electric Current

  4. Ampere (for Andre’ Ampere) Usually called an amp Open Circuit – break in the circuit, no current flow 11.1 Electric Current

  5. Short Circuit – when the load is bypassed Current increase Ground – allows for a continuous path for charge flow 11.1 Electric Current

  6. For historical reasons, current is defined as being in the direction that positive charge flows 11.1 Electric Current

  7. 11.3 Resistance and Ohm’s Law

  8. George Simon Ohm The actual values depend on the resistance of the conductor Called Ohm’s Law R – resistance measured in Ohms (W) 11.3 Resistance and Ohm’s Law

  9. Resistor – anything that uses electric energy Resistor – device used to control current The symbol for a resistor is 11.3 Resistance and Ohm’s Law

  10. The resistance value of a resistor is indicated by the colored bands on the resistor 11.3 Resistance and Ohm’s Law

  11. Misconceptions • Cells (batteries) do not put out a constant current. They maintain a constant potential difference. • Current passes through a wire and depends on the resistance of the wire. Voltage is across the ends of the wire. • Current is not a vector, it is always parallel to the conductor. The direction is from + to -. 11.3 Resistance and Ohm’s Law

  12. Misconceptions 4. Current or charge do not increase or decrease. The amount of charge in one end of the wire comes out of the other end. 11.3 Resistance and Ohm’s Law

  13. 11.5 Superconductors

  14. An element or compound that conducts electricity without resistance Become insulators above a critical temperature Uses MagLev Trains 11.5 Superconductors

  15. 11.6 Electrical Energy and Power

  16. The rate of energy flow for an electric circuit That is more commonly written as Combining with Ohm’s Law it can also be written 11.6 Electrical Energy and Power

  17. The power company charges by the kilowatt-hour (kWh) Just a cool picture 11.6 Electrical Energy and Power

  18. Household circuits – wires will heat up as current increases In a 20A household circuit In a 15A household circuit Circuits are typically designed to run at 80% of the rated power output Different circuits have different gauge wires (diameter) 11.6 Electrical Energy and Power

  19. Circuit Breakers and Fuses Break the circuit 11.6 Electrical Energy and Power

  20. 11.7 Sources of EMF

  21. EMF – electromotive force – the potential difference between the terminals of a source when no current flows to an external circuit (e) 11.7 Sources of EMF

  22. A battery will have an internal resistance (r) So there is a potential drop due to the current that travels through the cell So the actual potential across the terminals of a cell will be This is called the terminal voltage 11.7 Sources of EMF

  23. 11.8 Resistors in Series

  24. When resistors are place in a single pathway They are said to be in series A schematic would look like this 11.7 Sources of EMF

  25. The current in a series circuit is the same throughout the circuit The potential across the source of EMF is equal to the sum of the potential drops across the resistors 11.7 Sources of EMF

  26. Since potential can be defined as We can rewrite the equation for potential as 11.7 Sources of EMF

  27. 11.9 Resistors in Parallel

  28. When resistors are place in a multiple pathways They are said to be in parallel A schematic would look like this 11.9 Resistors in Parallel

  29. The potential difference in a parallel circuit is the same throughout the circuit The current through the source of EMF is equal to the sum of the current through the resistors 11.9 Resistors in Parallel

  30. Since current can be defined as We can rewrite the equation for potential as 11.9 Resistors in Parallel

  31. Circuits that contain both series and parallel components need to be solved in pieces This circuit contains 20W resistors in series 25W resistors and load series to each other and parallel to the 40W resistor 11.9 Resistors in Parallel

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