calculate resistance of copper wire 20m along and 0.05cm
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Neither. Resistance is in ohms, Ω.
What you're calling specific resistance, is, I believe, usually called resistivity.
And the resistance of a prism or cylinder of material with resistivity ρ, length L, and cross-sectional area A, is:
R = ρL/A
— — looks like you've multiplied twice by L, when it should be multiplied just once.
— — Or was that "*L=.." just supposed to be a footnote?
ρ = 1.678·10⁻⁶ Ω·cm = 1.678·10⁻⁶ Ω·cm(m/100cm) = 1.678·10⁻⁸ Ω·m
L = 20 m
A = ¼πD² = ¼π(0.05 cm)² = ¼π(0.0005 m)² = 0.78540·2.5·10⁻⁷ m² = 1.9635·10⁻⁷ m²
R = (1.678·10⁻⁸ Ω·m) (20 m) / (1.9635·10⁻⁷ m²)
= 1.71 Ω·m·m/m²
= 1.71 Ω
What you're calling specific resistance, is, I believe, usually called resistivity.
And the resistance of a prism or cylinder of material with resistivity ρ, length L, and cross-sectional area A, is:
R = ρL/A
— — looks like you've multiplied twice by L, when it should be multiplied just once.
— — Or was that "*L=.." just supposed to be a footnote?
ρ = 1.678·10⁻⁶ Ω·cm = 1.678·10⁻⁶ Ω·cm(m/100cm) = 1.678·10⁻⁸ Ω·m
L = 20 m
A = ¼πD² = ¼π(0.05 cm)² = ¼π(0.0005 m)² = 0.78540·2.5·10⁻⁷ m² = 1.9635·10⁻⁷ m²
R = (1.678·10⁻⁸ Ω·m) (20 m) / (1.9635·10⁻⁷ m²)
= 1.71 Ω·m·m/m²
= 1.71 Ω
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