Circuits
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Circuits

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Circuits Presentation Transcript

  • 1. Circuits March 30th, 2009
  • 2. Electric Circuits
    • A circuit is simply a closed loop through which charges can continuously move.
    • The word circuit is from
    • the same base as the
    • word circle, which
    • describes how the electrons move
  • 3. Requirements of a Circuit
    • There must be an energy supply capable doing work on charge to move it from a low potential energy to a high potential energy location. This establishes a potential difference (voltage) across the two ends of the external circuit.
    • There must be a closed
    • conducting loop in the circuit
    • which stretches from the
    • high potential, positive terminal
    • to the low potential, negative terminal.
  • 4. An analogy to help you…
    • A circuit is like a rollercoaster
      • It is a complete loop
      • There is a place where energy is put in to increase potential energy (a battery in a circuit and the chain pulling up the hill in the rollercoaster)
      • The rollercoaster naturally flows downhill just like charge in a circuit naturally flows from high potential to low potential
  • 5.
    • The diagram at the right shows a light bulb connected to a 12-V car battery. The + and - terminals are shown.
      • As a + charge moves through the battery
      • from D to A, it ________ (gains, loses) electric potential.
      • As a + charge moves through the external
      • circuit from A to D, ________ (gains, loses)
      • electric potential.
    • Use >, <, and = signs to compare the electric potential (V) at the four points of the circuit.
      • VA ___ VB ____ VC ____ VD
  • 6. Decide if each statement is true or false:
    • When an electrochemical cell no longer works, it is out of charge and must be recharged before it can be used again.
    • 2. An electrochemical cell can be a source of charge in a circuit. The charge which flows through the circuit originates in the cell.
    • 3. Charge becomes used up as it flows through a circuit. The amount of charge which exits a light bulb is less than the amount which enters the light bulb.
    • 4. The local electrical utility company supplies millions and millions of electrons to our homes everyday.
  • 7. All statements were FALSE!!
    • When a battery is “dead” it is out of energy required to push a charge from one terminal to another
      • This energy can be restored in some batteries with a reversible chemical reaction…so it is more like reenergizing than recharging your batteries
    • Batteries are the source of energy in a circuit, charges carry the energy
    • Charge is not used up in a circuit, energy is
    • Electrons are already in your home, the power company supplies the energy to these electrons
  • 8. Circuits
    • A circuit is a set of electrical components connected so they provide one or more complete paths for the movement of charges
    • A load is any component or group of components that dissipates energy
    • A simple circuit consists of a source of potential difference (electrical energy) and a load
  • 9. Drawing Circuits with Schematic Diagrams
    • Graphic representation
    • of an electric circuit
    • Uses standardized
    • symbols representing
    • circuit components
    • COPY DOWN
    • SYMBOLS FROM
    • OVERHEAD
  • 10. Light Bulbs
    • A light bulb contains
    • a complete conducting path
      • See Overhead
        • (regular and decorative lights)
    • A light bulb is considered
    • a load because it dissipates
    • electrical energy (by
    • converting it to light energy)
  • 11. EMF
    • Electromotive Force
      • The energy per unit charge supplied by a source of electric current
      • Any device that increases the potential difference and energy of charges circulating in a circuit
      • Current flow shows
      • the direction of +
      • charges
      • EMF shows the flow
      • of electrons
  • 12. Types of Circuits
    • Closed circuit
      • Path from one terminal to the other is complete. A potential difference exists and electrons move from one terminal to the other.
    • Open Circuit
      • No complete path. No charge flow and no current
    • Short Circuits
      • Without a load the circuit contains little resistance to the movement of charges.
      • This causes high current which can damage circuit components.
  • 13. Types of Circuits
    • Series Circuit
      • A circuit or portion of a circuit
      • that provides a single conducting
      • path without junctions
    • Parallel Circuit
      • A circuit or portion of a circuit in which two or more components are connected across a common point or junction, providing multiple conducting paths for the current
  • 14. Resistors in Series
    • Resistors in series all have the same current
    • The total (or equivalent) resistance can by found by finding the sum of all resistors
    • R EQ = R 1 + R 2 + ….
  • 15. Practice
    • A 9.0 V battery is connected in series to four resistors with values of 2.0  , 4.0  , 5.0  , and 7.0  . Find the equivalents resistance for the circuit and the current in the circuit.
    • Hint: Draw a diagram!
    • Answer: R= 18  and I=0.50A
  • 16. Resistors in Parallel
    • Resistors in parallel have the same potential difference (voltage) across them.
    • The sum of the currents in parallel resistors equals the total current
    • Equivalent resistance is the sum of the reciprocals
    • 1/R EQ = 1/R 1 + 1/R 2 + ….
  • 17. Practice
    • A 9.0 V battery is connected to four resistors in parallel with values of 2.0  , 4.0  , 5.0  , and 7.0  . Find the equivalents resistance for the circuit and the current in the circuit.
    • Hint: Draw a diagram!
    • Answer: R=0.917  and I =9.8 A