A section of superconducting wire carries a current of 90 A and requires 1.10 L

Question

A section of superconducting wire carries a current of 90 A and requires 1.10 L of liquid nitrogen per hour to keep it below its critical temperature. For it to be economically advantageous to use a superconducting wire, the cost of cooling the wire must be less than the cost of energy lost to heat in the wire. Assume that the cost of liquid nitrogen is $0.30 per liter, and that electric energy costs $0.10 per kW·h. What is the resistance in of a normal wire that costs as much in wasted electric energy as the cost of liquid nitrogen for the superconductor?

Explanation / Answer

Here the the two costs per hour are same,

1.10*0.30 = 90^2 *R*0.10/1000

1.1*0.3*1000/(0.1*90^2) =R

R = 0.4074 ohm answer

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