Copper wire has an electrical resistance of 4 ohms. What will be the resistance of this wire

Copper wire has an electrical resistance of 4 ohms. What will be the resistance of this wire if it is pulled through a special machine that increases the length by 3 times?

Resistance of a wire with cross-sectional area s, length l and resistivity ρ:

r = lρ / s.

The volume of the wire before elongation and after elongation is the same:

V = ls.

The length of the wire after lengthening l1 = 3l, and the section s1 must be found:

V = l1s1 = 3ls1;

ls = 3ls1;

s = 3s1;

s1 = s / 3;

Resistance of the wire after stretching:

r1 = l1ρ / s1 = (3lρ) / (s / 3) = 9 * lρ / s = 9r = 9 * 4 ohms = 36 ohms.

Answer: 36 ohms.