UNIT FIVE: Electricity and Magnetism

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UNIT FIVE Electricity and Magnetism

• Chapter 16 Electricity
• Chapter 17 Magnetism

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Chapter Sixteen Electricity

• 16.1 Charge and Electric Circuits
• 16.2 Current and Voltage
• 16.3 Resistance and Ohms Law
• 16.4 Types of Circuits

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Chapter 16.4 Learning Goals

• Build and analyze series and parallel circuits.
• Apply Ohms law to calculate the current in a
  circuit.
• Compare and contrast series and parallel circuits.

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Investigation 16C
Electric Circuits

• Key Question
• What are the different types of circuits?

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16.4 Types of circuits

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

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16.4 Series circuits

• Inexpensive strings of holiday lights are wired
  with the bulbs in series.
• If you remove one of the bulbs from its socket,
  the whole string of mini bulbs will go out.

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16.4 Current and resistance in series circuits

• Everything has some resistance, even wires.

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16.4 Current and resistance in series circuits

• If you know the resistance of each device, you
  can find the total resistance of the circuit by
  adding up the resistance of each device.

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16.4 Current and resistance in series circuits

• Think of adding resistances like adding pinches
  to a hose.
• Each pinch adds some resistance.

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Solving Problems

• A series circuit contains a 12-V battery and
  three bulbs with resistances of1O, 2 O, and 3 O.
• What is the current in the circuit?

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Solving Problems

• Looking for
• current (amps)
• Given
• Voltage 12V resistances 1O, 2 O, 3 O.
• Relationships
• Rtot R1R2R3
• Ohms Law I V R
• Solution
• Rtot 6 O
• I 12 V 6 O 2 amps

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16.4 Voltage drop

• As each device in series uses power, the power
  carried by the current is reduced.
• As a result, the voltage is lower after each
  device that uses power.
• This is known as the voltage drop.

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16.4 Voltage drop

• The law of conservation of energy also applies to
  a circuit.
• In this circuit, each bulb has a resistance of 1
  ohm, so each has a voltage drop of 1 volt when 1
  amp flows through the circuit.

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16.4 Voltage drop and Ohms law

• The voltage drop across a resistance is
  determined by Ohms law in the form V IR.
• The voltage drop (V) equals the current (I)
  multiplied by the resistance (R) of the device.

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16.4 Kirchhoffs Voltage Law

• Kirchhoffs voltage law states that the total of
  all the voltage drops must add up to the
  batterys voltage.

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Solving Problems

• The circuit shown contains a 9-volt battery, a
  1-ohm bulb, and a 2-ohm bulb.
• Calculate the circuits total resistance and
  current.
• Then find each bulbs voltage drop.

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Solving Problems

• Looking for
• total resistance voltage drop each bulb
• Given
• Voltage 9V resistances 1O, 2 O.
• Relationships
• Rtot R1R2R3
• Ohms Law I V R
• Solution- part 1
• Rtot 3 O
• I 9 V 3 O 3 amps

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Solving Problems

• Solution- part 2
• Use resistance to find current
• I 9 V 3 O 3 amps
• Solution- part 3
• Rearrange Ohms law to solve for voltage
• Use current to find each voltage drop
• V I x R
• V1 (3 A) x (1 O) 3 volts
• V2 (3 A) x (2 O) 6 volts (3 6 ) 9 V

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16.4 Parallel Circuits

• In parallel circuits the current can take more
  than one path.

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16.4 Kirchhoffs Current Law

• All of the current entering a branch point must
  exit again.
• This is known as Kirchhoffs current law.

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16.4 Voltage and parallel circuits

• If the voltage is the same along a wire, then the
  same voltage appears across each branch of a
  parallel circuit.

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16.4 Voltage and parallel circuits

• Parallel circuits have two advantages over series
  circuits.
• Each device in the circuit has a voltage drop
  equal to the full battery voltage.
• Each device in the circuit may be turned off
  independently without stopping the current in the
  other devices in the circuit.

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16.4 Current and parallel circuits

• Each branch works independently so the total
  current in a parallel circuit is the sum of the
  currents in each branch.

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16.4 Calculating in circuits

• In a series circuit, adding an extra resistor
  increases the total resistance of the circuit.
• In a parallel circuit, more current flows so the
  total resistance decreases.

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Solving Problems

• All of the electrical outlets in Jonahs living
  room are on one parallel circuit.
• The circuit breaker cuts off the current if it
  exceeds 15 amps.
• Will the breaker trip if he uses a light (240 O),
  stereo (150 O), and an air conditioner (10 O)?

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Solving Problems

• Looking for
• whether current exceeds 15 amps
• Given
• resistances 240 O 150 O 10 O
• Relationships
• Assume voltage for each branch 120 V
• Ohms Law I V R
• Kirchhoffs Current Law Itotal I1 I2 I3
• Solution
• Ilight 120 V 240 O 0.5 amps
• Istereo 120 V 150 O 0.8 amps
• Ia/c 120 V 10 O 12 amps

0.5 0.8 12.0 13.3
Breaker will not trip
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You are Wired!

• Your nervous system uses specialized cells called
  neurons to transfer electrical signals from one
  part of your body to another. A neuron has three
  basic parts the cell body a long, thin portion
  called the axon and fingerlike projections
  called dendrites.