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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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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 Materials

Materials 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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