Current Electricity

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Current Electricity
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How is current produced?

• When a high potential is connected by a
  conductive material to a low potential.
• Flow of electrons is called electric current.
• Units C/s Amperes (Amps)

High Potential
Low Potential
Equal Potential
Equal Potential
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High Potential
Low Potential
Electron Pump

• When the potentials are equal, the current stops
  flowing
• To increase the potential of the electrons an
  electron pump must convert (do work) another form
  of energy into electrical potential energy.
• Electron pump examples
• Voltaic or galvanic cell (dry cell)
• Several cells connected (Battery)
• Photovoltaic cell (solar cell)
• Generator

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Two types of current

• Direct Current (D.C.) Flow of electrons in only
  one direction
• Battery
• Alternating Current (A.C.) Flow of electrons at
  first in one direction and then the other
  direction.
• Generator
• In your House
• 60 Hertz

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What affects current flow?

• Potential Difference Voltage
• Resistance - slowing or reduction of the flow of
  current
• Resistance depends on the material, length of
  material, and the cross sectional area of the
  material through which the current is moving.

R is resistance, r is resistivity, L is
length, A is the cross sectional area
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Ohms Law

• Ohms Law stated The ratio of V/I is a
  constant, where V is the voltage applied across a
  piece of material (such as wire) and I is the
  current through the material. R is the
  resistance of the piece of material.
• Units Ohms (W) Volt/amp

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Electric Power

• When there is current (I) in a circuit as a
  result of a voltage (V), the electric power (P)
  delivered to the circuit is
• Units watts amp x volt J/s

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Electric Power

• Many electrical devices become hot when provided
  with sufficient electric power. Toasters, irons,
  space heaters, heating elements in electric
  stoves, and incandescent light bulbs. In such
  cases it is possible to obtain two equivalent
  power equations
• When electric energy is transferred into thermal
  energy in a resistor, the increase in thermal
  energy is
• units Kilowatt hour or Joules

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Current in electric Circuits

• An electric Circuit is a closed loop.
• Basic Circuits consist of three things
• Electron pump (Battery)
• Device that reduces potential. (User)
• Conducting connections (Wires)

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Direct Current Circuits

• Circuit closed loop in which current can flow
• Basic simple circuit
• Voltage source
• Voltage uses
• conducting connections (wire)
• Diagrams for electric circuits
• Describe in words
• use photographs/drawings
• Use symbols (schematics)

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Schematic Symbols
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Drawing Schematic Circuits

• Draw symbol for battery and indicate and -
  terminals
• Draw wire from to the voltage user and draw
  its symbol.
• If a point where there are two current paths,
  draw connection symbol and follow one path to the
  user. Return to the second path and draw to its
  user and continue until paths join.
• Follow path to the - terminal
• Check work
• Connect ammeter in series
• Connect voltmeter in parallel

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Objectives

• Describe the configuration of a working circuit
• Interpret circuit diagrams
• Describe the characteristics of series
  connections
• Determine equivalent resistance of circuits
  having two or more resistors.
• Explain the cause of short circuits
• Homework
• Read Pages 531-541
• Pg 534 1-3, Pg 537 6-9

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Series Circuits

• Only one path for current to follow
• User followed by another user (ie. Resistor
  followed by a light)

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Series Circuit Rules

• Current is the same for each user
• The effective resistance is the sum of all
  resistors in the series
• The sum of the voltage drop is equal to the total
  voltage drop

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Parallel Circuits

• Two or more paths for current to follow

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Parallel Circuit Rules

• Total current in the circuit is the sum of the
  current in all its paths (branches)
• The equivalent resistance decreases with more
  parallel resistors
• Voltage is the same in each path.

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Objectives

• Describe the configuration of a working circuit
• Distinguish between series and parallel circuits
• Describe the characteristics of series
  connections and of parallel connections.
• Interpret circuit diagrams
• Determine equivalent resistance of circuits
  having two or more resistors.
• Explain the cause and prevention of overloading
  household circuits.
• Homework
• Read Pages 531-541
• Pg 534 1-3, Pg 537 6-9