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
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Energy

• Pair of Charges

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Electric Potential

• 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.

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Potential Difference
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Potential Difference
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Potential Difference

• Back to the zero point?A convenient zero point
  to chose 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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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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Circuit Analogy
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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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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

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Reading and Homework

• Read Chapter 17
• pp 593 - 625

• HW due on test day
• p 599 1-3 p 601 2, 3, 5-9
• p 607 1 4 (B) p609 1 5
• p 615 1 6 p 616 2-4, 7,9
• p 621 1 5
• Extra Practice
• p 626 628 11, 20 54