... = 227 V/m 30 We use R ∝ L/A The diameter of a 22-gauge wire is 1/4 that of a 10-gauge wire Thus from R = ρL/A we find the resistance of 25 ft of 22-gauge copper wire to be R = (1.00 Ω) (25 ft/1000... absolute values of the slopes (for the straight-line segments shown in the graph of Fig 2 6-2 6(b)) are equal to the respective electric field magnitudes Thus, applying Eq 2 6-5 and Eq 2 6-1 3 to the three... where L is the length of the wire, ρ is the resistivity of copper, and A is the cross-sectional area of the wire Since each turn of wire has length 2πr, where r is the radius of the coil, then L