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

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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 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

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
- Radius of wire
- 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!

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