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physics electric and current circuit

Physics
Tutor: None Selected Time limit: 0 Hours

A carbon rod with a radius of 1.4 mm is used 

to make a resistor. 
What length of the carbon rod should be 
used to make a 1.3 Ω resistor? The resistivity 
of this material is 3.9 × 10−5 Ω · m . 
Answer in units of mm.
Apr 11th, 2015

R = ρL/A 

ρ is resistivity of the material in Ω-m 

L is length in meters 

A is cross-sectional area in m² 

A = πr² = π(0.0014)² = 4.39e-3 m² 

1.3 = (3.9e-5) L / (4.39e-3) 

L = [ 1.3 * (4.39e-3) ] / (3.9e-5)

L = 146.33 mm or 0.14633 m

Apr 11th, 2015

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Apr 11th, 2015
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