What happens to electrons in the filament?

 

 

Is resistance in a wire always bad?

School blocks YouTube? Use the file below.

bulbResistance.mp4

 

Show Me The Physics
YouTube Channel

 

 

Fill in the Blank Notes

 

 

2) The resistance in a wire depends on:

 

 

a) resistivity - ρ  a metals structural resistance to electron flow

p. 4 Reference

 

b) Length (L) of the wire

 

 

 

c) Thickness (Cross Sectional Area) of the wire (A)

 

Why do powerful

speakers require

thick speaker wire?

[ Flash ]

 

"Large speakers draw a lot

of current. Thick wires have

lower resistance"

 


 

R = ρL/A 

Ex) R, A relationship?

 

 

 

Inverse relationship

4 

 

R = ρL/A 

 

 

Ranking Task

Rank the resistance of the wires below from smallest to largest.

 

 

 

 

 

 

 

AP Physics B


Giancoli p. 516) 16

 

 

L and R are direct

L + 4L = Total Length = 5 L

Cut the wire at 20 % of total length

 

Since wire R = 10 ohms

 

R1 = 2 ohms, R2 = 8 ohms

 

 

 

 

[ Flash ]

 

 

 

 

3) Resistance and Temperature

(Double Click on Picture above to start video)

Full Size Video

 

Scientific Advisors: Dr. Saul Dushman; Dr. Roman Smoluchowski; Dr. David Harker

Prelinger Archives

Production Company: Wolff (Raphael G.) Studios, Inc. Audio/Visual: sound, color
Creative Commons license: Public Domain

 

 

 

Metals

 

T down, R down

 

T up, R up

 

 

 

 

(many electrical devices
 have fans to decrease T)

 

 


 

Nonmetals – When temperature increases, resistance decreases 

 

Superconductor - conductor with no resistance

 

Achieved only at very low temperatures
(expensive now)

 

 

 

 

 

 

 

 

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