Series and Parallel Circuits

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Series and Parallel Circuits
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Review of Chapter 22

• A flow of charged particles is called an electric
  Current.
• A Flow of one Coulomb/second is equal to 1
  ampere. We write this as 1A
• A device for measuring current is an Ammeter.
• The potential energy of an electrical charge is
  termed the Electric Potential Difference.
• Electric Potential is measured in Joule/Coulomb
  and is called the Volt (V)
• A device for measuring Voltage is a Voltmeter.

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Review of Chapter 22

• Resistance (R) is the opposition to current flow
  and is represented by the Ohm (O).
• Ohms Law is R V/I
• Power (P) is the energy/time converted into some
  other form of energy by the circuit.
• Power is measured in Watts (W).
• To find Power P VI or P I2R
• Energy Pt (Power x time) or E I2Rt in Joules
  (J)

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Some Symbols
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Example of a Simple Circuit
The Voltmeter is measuring across a battery and
resistor. The ammeter is measuring current
through the circuit.
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Series and Parallel Circuits

• Objective of this chapter
• Discuss Series Circuits
• Identify Voltage Drops in a Series Circuit
• Discuss Parallel Circuits
• Identify Voltage Drops is a Parallel Circuit
• Equivalent Resistance
• Ammeters and Voltmeters

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Series Circuits

• Only one Path for current to flow through.
• All current travels through each resistor.
• The total resistance of the circuit is the sum of
  all resistors in the circuit. R R1 R2 R3
• The Current through the circuit is
  
  
  I V/(R1 R2
  R3)
• The Voltage V V1 V2 V3
• Find the equivalent resistance and then use
  R V/I

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Series Circuit Example
E 120V and R1, R2 and R3 are all 20 O
resistors. What is the effective resistance of
the circuit? What is the current in the circuit?
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Voltage Drops in a Series Circuit

• The change in Electric Potential around a series
  circuit is Zero.
• If you have a 9V battery, the voltage dropped
  around the circuit will equal -9V
• The circuit to the right is called a Voltage
  Divider

A1
ms
V1
5 oh
E
R1

45V
10 ohms
V2
R2
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Parallel Circuits

• In a Parallel circuit there are many paths for
  current to follow. Current follows the path of
  least resistance.
• The Potential Difference is the same across each
  path.
• The total current is the sum of the currents in
  each path I I1 I2 I3
• The equivalent resistance is found by
• 1/R 1/R1 1/R2 1/R3

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Equivalent Resistance

• 1/R 1/R1 1/R2 1/R3

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Parallel Circuits
If R1 60 ohms, R2 30 ohms, R3 20 ohms , E
90V a) Find Req b) Find I for the
circuit c) Find I for each branch circuit
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Combined Circuits

• Many circuits combine both series and parallel
  circuits.
• Using combined circuits enables a wide variety of
  controls over current and voltage.
• Simplifying these circuits consists of 3 steps
• If resistors are in parallel, replace with an
  Req.
• If Resistances are then in series, determine the
  new Req
• Repeat steps 1 and 2 until the circuit is reduced
  to an equivalent resistance.

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Req in a Combined Circuit
Simplifying these circuits consists of 3
steps If resistors are in parallel, replace with
an Req. If Resistances are then in series,
determine the new Req Repeat steps 1 and 2 until
the circuit is reduced to an equivalent
resistance.
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Voltmeters Ammeters

• Voltmeters are used to measure voltage drop
  across some part of a circuit.
• Voltmeters have a very high resistance 10MO
• Ammeters measure current through the circuit.
• Ammeters have a very low resistance.
• Voltmeters work in Parallel.
• Ammeters work in Series.

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Recap

• Series Circuits have one path for current.
• Parallel Circuits have many paths for current.
• Series Req is R1R2R3R4 etc.
• Parallel Req 1/R(1/R1)(1/R2)(1/R3) etc.
• Combined Circuits need to be simplified in a step
  by step manner.
• Ammeters work in series while voltmeters work in
  parallel.

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Housekeeping

• Tutorial tomorrow evening covering waves and
  sound.
• Test Friday Morning.
• Labs this week will investigate various circuits.
• Assignment for Chapter 23
• Problems 1, 5, 6, 10, 13, 14, 15, 16, 17, 18
• Due as per normal assignment guidelines.
• You can find my website (with physics stuff) at
  http//electronics.saintjohn.nbcc.nb.ca/mcdevitt/

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Thank You