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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

• Polarization vs. Conduction

• Batteries, Current, Resistance

• Ohm’s Law and Examples

• Resistivity and Examples

• Power and Examples

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

• 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

• Battery

• Electrochemical

• Source of voltage

• Positive and negative

• 1.5 volt, 3 volt, 9 volt, 12 volt

• Circuit symbol

• Current

• Coulombs/second = amps

• I = ΔQ / Δt

• Example 18-1

• Requires complete circuit

• Circuit diagram

• Positive vs. negative flow

• 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

• 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

OK, but do not touch the other wire!

(heat of vaporization of squirrel)

• 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)

• Area of wire from resistivity and length

• Voltage Drop along wire

• Along x

• Along y

• Along z

• Work done/ loss of PE for (+) going with field

• No ½ because voltage is constant

• Alternate forms

P=IV = I2R = V2/R

V

+

0

• Calculate current

• Calculate Resistance

• In one step

• Power

• Electric Company charges for energy not power

• But instead of using Joules, they use kW-hours

• Problems 31, 32, 33, 38,

• 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

• At 12,000 V current must be

• Voltage drop along wire will be

• Power wasted in wire will be

• At 50,000 V current must be

• Voltage drop along wire will be

• Power wasted in wire will be

• 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!