Electricity Theory

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Electricity Theory

• VIR PIV and Capacitors!!!

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Energy
PEg

• When an object is at some height in a
  gravitational field it is said to have
  gravitational potential energy, PEg

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Energy

• Like gravitational fields causing masses to have
  potential energy, Electric Fields cause charges
  to have electric potential energy, PEE
• PEE is a type of mechanical energy
• MEtotal KE PEg PEs PEE

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Energy

• To give something PE you must do work (apply
  force over a distance) on the something (raising
  up in g-field)
• For PEE to occur a FE must be applied by either
• An E-Field (uniform)
• A pair of charges

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Energy

• Uniform E-field

A
B
Line Color Red E-Field Black Equipotential
lines Blue charge displacement
The negative sign indicates that the PEE will
increase if q is negative and decrease if q is
positive.
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Energy

• Pair of Charges

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Electric Potential, V

• Any point in an electric field is said to have
  Electric Potential, V.
• However, only a Difference in PE is measurable
  (remember zero point) so we talk of electric
  potential difference AKA potential difference,
  ?V. (see next slide)

1 C 6.2 X 1018 electrons
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Potential Difference, ?V
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Potential Difference, ?V (Zero point is
arbitrary)
1 C of charge moves through a ?V of 1.5 V to
produce 1.5 J of energy, which is used to run
electronic equipment.
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Potential Difference
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Potential Difference

• Back to the zero point?A convenient zero point
  to choose in a circuit or any electric system is
  the ground

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Battery (cells)

• A battery produces electricity by transforming
  chemical energy into electrical energy

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Ni-Cd Batteries

• http//go.hrw.com/resources/go_sc/phy/hf6neh_elc_i
  nt_c.pdf

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Battery
Carbon Electrode

Zinc Electrode
Sulfuric Acid
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Capacitor

• A capacitor is a storehouse of charge and energy
  that can be reclaimed when needed for a specific
  application
• A capacitor will only charge to the potential
  difference between the terminals of the battery

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Capacitance

• Capacitance, C The ability of a conductor to
  store energy in the form of electrically
  separated charges
• Capacitance is the ratio of charge to potential
  difference

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Capacitance

• Capacitance depends on size and shape

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Capacitor

• Energy stored in a capacitor

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Electric Current

• Movement of electric charge
• Rate of charge movement

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Charge Movement
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Charge Movement
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Types of Current

• AC ? Alternating current ? charges continuously
  change direction forward and back at 60 Hz
• Example outlets (approx 120 V)
• DC ? Direct current ? charges move in one
  direction
• Example batteries
• AC-DC Debate births the Electric Chair

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Circuit Analogy
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Resistance

• Resistance is the impedance of the motion of
  charge through a conductor
• The ratio of potential difference across a
  conductor to the current it carries

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Ohms Law
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Resistance

• Depends on Length, cross sectional area,
  material, and temperature

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Resistance and Temp
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Resistance and Thickness
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Resistor

• An electronic element that provides a specified
  resistance.
• A current or voltage REGULATOR

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Power (its Electric!)

• Power Rate at which work is done. OR Rate at
  which energy is transformed
• Electric Power The rate at which charge carriers
  convert PEE into non-mechanical energy