A portable electric heater uses 23.8 A of current. The manufacturer recommends that an extension cord attached to the heater receive no more than 2.60 W of power per meter of length. What is the smallest radius of copper (resistivity 1.72 x 10-8 Ω·m) wire that can be used in the extension cord? (Note: An extension cord contains two wires.)

Answer 1

P =I²R
R =ρL/A= ρL/πr²

P =I² ρL/πr²
r=sqrt(I² ρL/πP)=...

L=2 m, I=23.8 A, P=2.6 W,
ρ= 1.72 x 10 ⁻⁸ Ω