Is resistance in a wire always bad?

School blocks YouTube? Use the file below.

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

 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

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

Production Company: Wolff (Raphael G.) Studios, Inc. Audio/Visual: sound, color

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)