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Electric Circuits

Electric Circuits. Chapter 35. A Battery and a Bulb. In order to light a light bulb, you must have a complete circuit Circuit – any complete path along which charge can flow

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Electric Circuits

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  1. Electric Circuits Chapter 35

  2. A Battery and a Bulb • In order to light a light bulb, you must have a complete circuit • Circuit – any complete path along which charge can flow • Electrons flow from the negative part to the positive part of the battery through the wire and whatever else is in its path • The electrons do not “squash up” and concentrate in certain places; they flow continuously around a circuit

  3. A Battery and a Bulb

  4. Electric Circuits • Any path along which electrons can flow is a circuit • For a continuous flow of electrons, there must be a complete circuit with no gaps • A gap is usually provided by an electric switch that can be opened or closed to either cut off or allow electron flow • In Series – applied to portions of an electric circuit that are connected in a row so that the current that goes through one must go through all of them • In Parallel – applied to portions of an electric circuit that are connected at two points and provide alternative paths for the current between those two points

  5. Electric Circuits

  6. Series Circuits • Series Circuit – devices are arranged so that charge flows through each in turn; if one part should stop current, it will stop throughout • Series circuits follow 5 important rules: • A break anywhere in the path stops the electron flow in the entire circuit • The total resistance is equal to the sum of individual resistances along the current path • The current is equal to the voltage divided by the total resistance • The voltage drop across each device is proportional to its resistance • The sum of voltage drops across the resistance of the individual devices is equal to the total voltage

  7. Series Circuits

  8. Parallel Circuits • Parallel Circuit – devices are connected to the same two points of the circuit, so that any single device completes the circuit independently of the others • Parallel circuits follow 4 important rules: • Each device connects the same two points of the circuit; the voltage is the same across each device • The amount of current in each branch is inversely proportional to the resistance of the branch • The total current is equal to the sum of the currents in the branches • As the number of parallel branches is increased, the overall resistance of the circuit is decreased

  9. Parallel Circuits

  10. Schematic Diagrams • Schematic Diagram – describes an electric circuit, using special symbols to represent different devices in the circuit • Resistance is shown as a zigzag line • A battery is represented with a set of short and long parallel lines (positive = long and negative = short)

  11. Schematic Diagrams

  12. Combining Resistors in a Compound Circuit 1 / Req = 1 / R1 + 1 / R2 + 1 / R3 + ...

  13. Combining Resistors in a Compound Circuit Req = R1 + R2 + R3 + ...

  14. What’s the Total Resistance? 10Ω

  15. Parallel Circuits and Overloading • Lines carrying an unsafe amount of current are overloaded • To prevent overloading, fuses or circuit breakers are inserted in lines that provide power • Excessive current will “blow out” the fuse or “trip” the circuit breaker, stopping the current • A short circuit is often caused by faulty wire insulation

  16. Parallel Circuits and Overloading

  17. Homework (due 4/16) • Read Chapter 35 (pg. 548-558) • Do #18-33 (560-561) • Do #1-8 in Appendix F (pg. 690)

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