What is the resistance between the ends of the welded bar at 20°C?
Two cylindrical bars, each with diameter of 2.40 cm, are welded together end to end. One of the original bars is copper and is 0.400 m long. The other bar is iron and is 0.200 m long. What is the resistance between the ends of the welded bar at 20°C?
Update:4.339e-5 was incorrect
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Verified answer
** The end -to-end resistance is 5.906 *10^ -5 Ω = 59.06 μΩ
Worked out for you,
To use R = ρL/A for each bar,
ρ for copper = 1.68 *10^-8 Ω.m, L =0.4m
ρ for copper = 1.0 * 10^-7 Ω.m, L = 0.2m
Bars have same area = π r² = π 0.012² . . . 2.40 cm Diam = 0.012m radius
Rtotal
= ρL/A for copper bar + ρL/A for iron bar
= [ ρL for copper + ρL for iron ] A . . .
=[1.68 *10^ -8 * 0.4m + 1.0 * 10^ -7 * 0.2] / ( π * 0.012² )
= 5.906 *10^ -5 = 59.06 μΩ = Answer
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