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Conduction and Current. Polarization vs. Conduction Batteries, Current, Resistance Ohm’s Law and Examples Resistivity and Examples Power and Examples. Electrical Properties of Materials. Materials can do 2 things:. Store charge Initial alignment of charge with applied voltage

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Presentation Transcript
conduction and current
Conduction and Current
  • Polarization vs. Conduction
  • Batteries, Current, Resistance
  • Ohm’s Law and Examples
  • Resistivity and Examples
  • Power and Examples
materials can do 2 things
Electrical Properties of MaterialsMaterials can do 2 things:
  • Store charge
    • Initial alignment of charge with applied voltage
    • Charge proportional to voltage
    • Temporary short-range alignment
  • Conduct charge
    • Continuous flow of charge with applied voltage
    • Current proportional to voltage
    • Continuous long-range movement
charge storage vs conduction
Charge Storage vs Conduction
  • Storage
  • Q = CV
  • Charge in Coulombs
  • Energy stored in Joules
  • Conduction
  • V= IR (I=GV G=1/R)
  • Charge flow in Coulombs/second (amps)
  • Power created or expended in Watts
batteries
Batteries
  • Battery
    • Electrochemical
    • Source of voltage
    • Positive and negative
    • 1.5 volt, 3 volt, 9 volt, 12 volt
    • Circuit symbol
current
Current
  • Current
    • Coulombs/second = amps
    • I = ΔQ / Δt
    • Example 18-1
    • Requires complete circuit
    • Circuit diagram
    • Positive vs. negative flow
resistance
Resistance
  • Resist flow of current (regulate)
  • Atomic scale collisions dissipate energy
  • Energy appears in other forms (heat, light)
  • Applications
    • Characterize appliance behavior
      • Heater (collisions cause heat)
    • Regulate current/voltage on circuit board
  • Resistors and color code
resistance and ohm s law
Resistance and Ohm’s Law
  • Storage vs. Conduction
    • Q = CV (storage)
    • I = GV (conduction)
    • Current proportional to voltage
    • Proportionality is conductance
  • Use inverse relation
    • V = IR
    • Resistance
    • Units volts/amps = ohms
  • Ohm’s law
    • If V proportional to I, ohmic
    • Otherwise non-ohmic
  • Example 18-3
ohm s law examples1
Ohm’s Law Examples

OK, but do not touch the other wire!

(heat of vaporization of squirrel)

resistivity vs resistance
Resistivity vs. Resistance
  • Property of material vs. property of device
  • Similar to dielectric constant vs. capacitance
  • Becomes resistance vs. resistivity
  • We use reciprocals, resistance and resistivity
  • ρ published for materials, like K.
  • High ρ poor conductor, σ good conductor (similar to K for storage)
resistivity example
Resistivity Example
  • Area of wire from resistivity and length
  • Radius of wire
  • Voltage Drop along wire
resistivity example1
Resistivity example
  • Along x
  • Along y
  • Along z
power
Power
  • Work done/ loss of PE for (+) going with field
  • No ½ because voltage is constant
  • Alternate forms

P=IV = I2R = V2/R

V

+

0

power example
Power example
  • Calculate current
  • Calculate Resistance
  • In one step
power example1
Power example
  • Power
  • Electric Company charges for energy not power
  • But instead of using Joules, they use kW-hours
power examples
Power examples
  • Problems 31, 32, 33, 38,
power transmission
Power transmission
  • All customer cares about to run his home or factory:
    • Can do low voltage at high current
    • High voltage at low current
    • Transformers can switch back and forth
power transmission 12 000 v
Power transmission – 12,000 V
  • At 12,000 V current must be
  • Voltage drop along wire will be
  • Power wasted in wire will be
power transmission 50 000 v
Power transmission – 50,000 V
  • At 50,000 V current must be
  • Voltage drop along wire will be
  • Power wasted in wire will be
power transmission 2 000 v
Power transmission – 2,000 V
  • At 2,000 V current must be
  • Voltage drop along wire will be
  • Power wasted in wire will be

<< Half the voltage and power are wasted!

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