Conduction and Current

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# Conduction and Current - PowerPoint PPT Presentation

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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## PowerPoint Slideshow about 'Conduction and Current' - lukas

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Presentation Transcript
Conduction and Current
• Polarization vs. Conduction
• Batteries, Current, Resistance
• Ohm’s Law and Examples
• Resistivity and Examples
• Power and Examples
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
• 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
• Battery
• Electrochemical
• Source of voltage
• Positive and negative
• 1.5 volt, 3 volt, 9 volt, 12 volt
• Circuit symbol
Current
• Current
• Coulombs/second = amps
• I = ΔQ / Δt
• Example 18-1
• Requires complete circuit
• Circuit diagram
• Positive vs. negative flow
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
• 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 Examples

OK, but do not touch the other wire!

(heat of vaporization of squirrel)

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
• Area of wire from resistivity and length
• Voltage Drop along wire
Resistivity example
• Along x
• Along y
• Along z
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
• Calculate current
• Calculate Resistance
• In one step
Power example
• Power
• Electric Company charges for energy not power
• But instead of using Joules, they use kW-hours
Power examples
• Problems 31, 32, 33, 38,
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
• At 12,000 V current must be
• Voltage drop along wire will be
• Power wasted in wire will be
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
• 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!