11.2 Series and Parallel Circuits

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11.2 Series and Parallel Circuits

• pp. 448 452

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Circuit Diagrams

• Engineers and designers of electrical circuits
  use special symbols that show the components and
  connections in a circuit.
• A drawing made with these symbols is called a
  circuit diagram.

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Circuit Diagrams

• Follow these rules when you draw circuit
  diagrams
• Always use a ruler to draw straight lines for
  the conducting wires.
• Make right-angle corners so that your finished
  diagram is a rectangle.

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Electric Circuit Diagrams and Symbols

• Conductor or wire
• To pass current very easily from one part of a
  circuit to another.

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Electric Circuit Diagrams and Symbols

• One Cell (battery)
• Supplies electrical energy
• The positive end is bigger than the negative end.

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Electric Circuit Diagrams and Symbols

• Two Cells (battery)
• A battery can consist of one or several cells

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Electric Circuit Diagrams and Symbols

• Lamp
• A load that converts electrical energy to light
  energy

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Electric Circuit Diagrams and Symbols

• Ground
• A connection to earth

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Electric Circuit Diagrams and Symbols

• Resistor
• A resistor restricts the flow of current,

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Electric Circuit Diagrams and Symbols

• Switch
• allows current to flow only when it is in the
  closed (on) position

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Electric Circuit Diagrams and Symbols

• Ammeter
• Device that measures current
• Connected in series

A
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Electric Circuit Diagrams and Symbols

• Fuse
• A safety device melts to open the circuit if
  current exceeds a safe level

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Electric Circuit Diagrams and Symbols

• Voltmeter
• Device that measures voltage
• Connected in parallel (i.e. around the source or
  load you are measuring)

V
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Electric Circuit Diagrams and Symbols

• Motor
• electrical load that converts electrical energy
  into movement

M
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Series Circuits

• Electric circuit in which the components are
  arranged one after another in series.
• A series circuit has only one path along which
  electrons can flow.
• If that pathway is interrupted, the whole circuit
  cannot function.

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Series Circuits

• The amount of current is the same in all parts of
  a series circuit.
• If more resistors are added, it will increase the
  total resistance of the circuit.
• This decreases the current.

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Series Circuits

• Example Adding an extra bulb to a series string
  of lights makes all the bulbs dimmer.
• Electrons use up all their potential difference
  going around a series circuit no matter how many
  loads are in the circuit. Each load will use part
  of the total potential difference, depending on
  how much it resists the flow of electrons.

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Parallel Circuits

• A parallel circuit is an electric circuit in
  which the parts are arranged so that electrons
  can flow along more than one path.
• An interruption or break in one pathway does not
  affect the other pathways in the circuit.

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Parallel Circuits

• Similarly, adding a new pathway with more
  resistors does not affect the resistance in any
  of the other pathways. Adding extra resistors in
  parallel decreases the total resistance of the
  circuit.

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Parallel Circuits

• Each electron has the same amount of energy, and
  electrons must expend all their energy on the
  path they are on.
• This is why the potential difference across
  parallel resistors will always be the same, even
  though the resistors themselves are of different
  values

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• Loads connected in parallel circuits have
  different currents

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Summary of Current, potential difference, and
resistance in series and parallel circuits.
Circuit Potential Difference
Series circuit Each load uses a portion of the total potential differences supplies by the battery
Parallel circuit Each load uses all the potential difference supplied by the battery.
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Summary of Current, potential difference, and
resistance in series and parallel circuits.
Circuit Current
Series circuit The current is the same throughout a series circuit
Parallel circuit The current divides into different paths. A pathway with less resistance will have a greater current
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Summary of Current, potential difference, and
resistance in series and parallel circuits.
Circuit Resistance
Series circuit The current decreases when more resistors are added
Parallel circuit Adding resistors in parallel decreases the total resistance of the circuit.
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Two Types of Circuits Combined

• Series circuits and parallel circuits make up the
  circuits in your home and school.

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Two Types of Circuits Combined

• Some circuits are combinations of series circuits
  and parallel circuits.
• These combinations help prevent problems such as
  the all the lights in the house going out because
  one bulb burnt out.

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• It is also an important safety feature in a
  combination circuit to have some switches wired
  in series, because it is sometimes necessary to
  turn off the electricity in part or all of a home

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Homework

• Read pp. 448 452
• Answer the following questions
• p. 453 1 5
• p. 457 2 5, 7