Resistance in a Wire | Show Me The Physics

Resistance in a Wire lesson illustration

What happens to electrons in the filament?

Is resistance in a wire always bad?

School blocks YouTube? Use the file below.

bulbResistance.mp4

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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

Resistance in a Wire lesson illustration

b) Length (L) of the wire

Resistance in a Wire lesson illustration

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

Resistance in a Wire lesson illustration

Why do powerful

speakers require

thick speaker wire?

Resistance in a Wire lesson illustration

[ Flash ]

"Large speakers draw a lot

of current. Thick wires have

lower resistance"

R = ρL/A

Ex) R, A relationship?

R v A hoices

Inverse relationship

R = ρL/A

Ranking Resistance in a Wire lesson illustration Task

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

Resistance in a Wire lesson illustration

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

Resistance in a Wire lesson illustration

[ Flash ]

Resistance in a Wire lesson illustration

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

Resistance in a Wire lesson illustration

Metals

T down, R down

T up, R up

Resistance in a Wire lesson illustration

(many electrical devices
have fans to decrease T)

Resistance in a Wire lesson illustration

Nonmetals – When temperature increases, resistance decreases

Superconductor - conductor with no resistance

Achieved only at very low temperatures
(expensive now)

Check Your Understanding

5 quick questions — pick an answer to see if you’re right.

1. A wire's length is doubled while its material and thickness stay the same. Its resistance:

2. Why do powerful speakers need thick speaker wire?

3. A uniform 10 Ω wire is cut into two pieces, one 20% and one 80% of the length. What are their resistances?

4. As a metal wire gets hotter, its resistance:

5. A superconductor is a material that:

Wire-Resistance Questions →