Circuits

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Circuits
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Reviewing terms
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Series and Parallel Circuits

• Key Question
• How do series and parallel circuits work?

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Series and Parallel Circuits

• In series circuits, current can only take one
  path.
• The amount of current is the same at all points
  in a series circuit.

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Adding resistances in series

• Each resistance in a series circuit adds to the
  total resistance of the circuit.

Rtotal R1 R2 R3...
Total resistance (ohms)
Individual resistances (W)
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Total resistance in a series circuit

• Light bulbs, resistors, motors, and heaters
  usually have much greater resistance than wires
  and batteries.

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Voltage

• Voltage is the rate at which energy is drawn from
  a source that produces a flow of electricity in a
  circuit expressed in volts

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Voltage in a series circuit

• Each separate resistance creates a voltage drop
  as the current passes through.
• As current flows along a series circuit, each
  type of resistor transforms some of the
  electrical energy into another form of energy

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Series and Parallel Circuits

• In parallel circuits the current can take more
  than one path.
• Because there are multiple branches, the current
  is not the same at all points in a parallel
  circuit.

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Series and Parallel Circuits

• When analyzing a parallel circuit, remember that
  the current always has to go somewhere.

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Voltage and current in a parallel circuit

• In a parallel circuit the voltage is the same
  across each branch because each branch has a low
  resistance path back to the battery.
• The amount of current in each branch in a
  parallel circuit is not necessarily the same.
• The resistance in each branch determines the
  current in that branch.

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Advantages of parallel circuits

• Parallel circuits have two big advantages over
  series circuits
• 1. Each device in the circuit sees the full
  battery voltage.
• 2. Each device in the circuit may be turned off
  independently without stopping the current
  flowing to other devices in the circuit.

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Short circuit

• A short circuit is a parallel path in a circuit
  with zero or very low resistance.
• Short circuits can be made accidentally by
  connecting a wire between two other wires at
  different voltages.
• Short circuits are dangerous because they can
  draw huge amounts of current.

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Resistance in parallel circuits

• Adding resistance in parallel provides another
  path for current, and more current flows.
• When more current flows for the same voltage, the
  total resistance of the circuit decreases.
• This happens because every new path in a parallel
  circuit allows more current to flow for the same
  voltage.

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Electric Power, AC, and DC Electricity

• Key Question
• How much does electricity cost and what do you
  pay for?

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Electric Power, AC, and DC Electricity

• The watt (W) is a unit of power.
• Power is the rate at which energy moves or is
  used.
• Since energy is measured in joules, power is
  measured in joules per second.
• One joule per second is equal to one watt.

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Power in electric circuits

• One watt is a pretty small amount of power.
• In everyday use, larger units are more convenient
  to use.
• A kilowatt (kW) is equal to 1,000 watts.
• The other common unit of power often seen on
  electric motors is the horsepower.
• One horsepower is 746 watts.

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Paying for electricity

• Electric companies charge for the number of
  kilowatt-hours used during a set period of time,
  often a month.
• One kilowatt-hour (kWh) means that a kilowatt of
  power has been used for one hour.
• Since power multiplied by time is energy, a
  kilowatt-hour is a unit of energy.

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Alternating and direct current

• DCDirect Currentproduced by solar cells and
  chemical cells (batteries)
• Current only flows in one direction.
• One end of the battery is positive and the other
  end is negative.

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Alternating and direct current

• ACAlternating Current
• Current flows back and forth (alternates)
• Found in homes
• Generators produce AC current

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Application Wiring in Homes and Buildings
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Application Wiring in Homes and Buildings
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Toll RoadCircuit Analogy
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Toll Booth Explanation

• Adding toll booths in series increases resistance
  and slows the current flow.
• Adding toll booths in parallel lowers resistance
  and increases the current flow.

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Batteries in Series Parallel