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Series and Parallel Circuits

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Circuits

  • In order for electricity to flow we need
    • Power source
    • Closed circuit

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  • There are two type of circuits we will explore
    • Series circuit
    • Parallel circuit

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Series Circuit

  • In a series circuit there is only one path for the electrons to flow
    • In other words all the components are in series with each other

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  • Because there is only one path each charge will go through each resistor

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Predict, Test and Explain

  • How will the brightness of the bulbs change as we add more in series?

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  • What does this imply about the current in the circuit?

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+

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Parallel Circuit

  • In a Parallel circuit there are multiple pathways for charge to flow
    • Each device is placed on it’s own separate branch

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  • Current goes through each of the branches at the same time

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Predict, Test and Explain

  • How will the brightness of the bulbs change as we add more in parallel?

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  • What does this imply about the current in the circuit?

+

+

+

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Key Concepts

  • Bulbs in series represent a source of resistance to current flow, similar to boulders in a stream which can block the flow of water
  • Bulbs in parallel offer additional pathways for current flow, similar to branches of a stream which can carry more water.

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Calculating Resistance in Series Circuits

  • The rule for calculating Series Circuits is to…
  • Add up the values of each individual in the series.
  • R1 + R2 + R3…
  • 5 + 5 + 10
  • 20 Ω (ohms)

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Calculating Resistance in Series Circuits

  • Add up the values of each individual in the series.
  • R1 + R2 + R3…
  • 10 + 20 + 10
  • 40 Ω (ohms)

10

20

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Calculating Resistance in Series Circuits

  • The rule for calculating Series Circuits is to…
  • Add up the values of each individual in the series.
  • 1    1     1   1  �-- = -- + -- + --  �Rt   R1   R2   R3
  • 1    1    1    1  �-- = -- + -- + --  �Rt   4    4     2

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  • 1

-- = .25 + .25 + .5 

Rt

  • 1

-- = 1

Rt

  • 1

-- = 1

Rt

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20

  • 1

-- = 1

Rt

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  • 1

-- = Rt

1

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  • Rt = 1 Ω (ohms)

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Calculating Resistance in Series Circuits

  • The rule for calculating Series Circuits is to…
  • Add up the values of each individual in the series.
  • 1    1     1   1  �-- = -- + -- + --  �Rt   R1   R2   R3
  • 1    1    1 1  �-- = -- + -- + --  �Rt  100   200     1000

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  • 1

-- = .01 + .005 + .001 

Rt

  • 1

-- = .016

Rt

  • 1

-- = .016

Rt

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20

  • 1

-- = Rt

.016

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  • Rt = 62.5 Ω

(ohms)

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100

200

1000