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May 20, 2016
Resistance of a Wire
1. What is the cause of resistance in a wire?
Collisions between conduction electrons and lattice ions
Symbol:
Factors
Units:
Symbol
Unit
Less
Resistance
More
Resistance
Relationship
Length
Cross-sectional
Area
Resistivity
Temperature
Resistance of a Wire
What type of wire is the best conductor (least resistance)?
Formula for a
conducting wire at a
constant temperature . . .
May 20, 2016
Resistance of a Wire
2. What are the properties of wire that is the best conductor (has
the least resistance)?
short, wide area, good conductor
3. What are the properties of wire that is the worst conductor
(has the most resistance)? long, thin, bad conductor
4. To make a wire with the lowest resistance, what material
would you use? Highest resistance?
silver - best conductor
5. What is the resistance of a copper wire 2.0 meters long with
a cross-sectional area of 6.4×10-8 m2?
6. a) What is the resistance of a nichrome wire 12 meters long
with a diameter of 2.7×10-4 meter?
b) if the diameter of the wire above is doubled, what is its
resistance?
May 20, 2016
Simple Circuits and Schematics
Schematic: diagram using symbols to represent circuit elements
For each circuit shown below, draw a corresponding schematic
diagram using appropriate Circuit Symbols
1. Actual Circuit
Schematic Diagram of Circuit
2. Actual Circuit
Schematic Diagram of Circuit
May 20, 2016
Water Analogy for a Simple Circuit
Electric Circuits
1. For the electric circuit shown, what is the potential (voltage) at:
2. For the electric circuit shown, what is the potential difference from:
May 20, 2016
Electromotive Force (emf): conversion from some other form of
energy into electrical energy voltage rise, potential increase
Potential difference (pd): conversion from electrical energy into
some other form of energy voltage drop, potential decrease
Resistance in an Electric Circuit
Variable:
V
I
R
Quantity:
Units:
Type:
Electrical resistance: ratio of applied potential difference to current
Formula:
May 20, 2016
Resistance in an Electric Circuit
3. What is the resistance of a small appliance that draws 3.00 A
at 120 Volts?