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Circuits

Circuits. Chapter 35 Notes. Review: Series Circuits. Electric current has only one pathway through the circuit The current passing through each electric device is the same The current is resisted by the resistance of the first device, the resistance of the second, and third….

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Circuits

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  1. Circuits Chapter 35 Notes

  2. Review: Series Circuits • Electric current has only one pathway through the circuit • The current passing through each electric device is the same • The current is resisted by the resistance of the first device, the resistance of the second, and third…. • The total resistance to current is the sum of the individual resistances along the circuit path • The current is numerically equal to the voltage divided by the total resistance (Ohm’s Law) • Ohm’s Law also applies to each individual device

  3. Solving Series Circuits The current is the same in every resistor; this current is equal to that in the battery. The sum of the voltage drops across the individual resistors is equal to the voltage rating of the battery. The overall resistance of the collection of resistors is equal to the sum of the individual resistance values, Rtot = R1 + R2 + R3 + ...

  4. Series Parallel Resistance: Rtot = R1 + R2 + R3 + ... Current: Ibattery = I1 = I2 = I3 = ... Voltage: Vbattery= V1 + V2 + V3 + ... TBA

  5. Series Parallel Check: Draw a diagram for a series circuit: two 3 ohm resistors, one 9 V battery What is the equivalent resistance? What is the total current? What is the current at each resistor? If one resistor has a voltage drop of 4 V, what is the voltage drop of the other resistor? TBA

  6. Review: Parallel Circuits • Current has multiple paths to follow, each device operates independently of other devices • Voltage is the same across each device • The total current in the circuit divides among the parallel branches • Ohm’s Law applies separately to each branch • Total current in the circuit is equal to the sum of the currents of the parallel branches • As the number of parallel branches is increased, the overall resistance is decreased

  7. Solving Parallel Circuits The voltage drop is the same across each parallel branch. The sum of the current in each individual branch is equal to the current outside the branches. The equivalent or overall resistance of the collection of resistors is given by the equation 1/Req = 1/R1 + 1/R2 + 1/R3 ...

  8. Series Parallel Resistance: Rtot = R1 + R2 + R3 + ... Current: Ibattery = I1 = I2 = I3 = ... Voltage: Vbattery= V1 + V2 + V3 + ... Resistance: 1/Req = 1/R1 + 1/R2 + 1/R3 ... Current: Itotal = I1 + I2 + I3 + ... Voltage: Vbattery= V1 = V2 = V3 = ...

  9. Series Parallel Series check Q’s Check: Draw a parallel circuit diagram: two 3 ohm resistors, one 9 V battery What is the equivalent resistance? What is the total current? What is the voltage drop at each resistor?

  10. Compound Circuits • Some circuits are combinations of series and parallel circuits • To find equivalent resistance of the circuit, use the rules for both series and parallel

  11. Overloading Parallel Circuits • Review: In parallel circuits, adding branches increases circuit • This can be an issue with electrical lines in the home! • Lines that carry more than a safe amount of current are called overloaded • The heat can melt the insulation and start a fire

  12. Fuses and Circuit Breakers • Fuses connected in series prevent overloading • The entire line current must pass through the fuse • When the current gets too big, the wire in the fuse will melt and break the circuit • ‘blowing a fuse’ • Circuit Breakers also prevent overloading, but do not require replacement • When the current gets too big, the circuit breaker opens a switch, and breaks the circuit • Current through a circuit breaker

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