Answer:
L = 6.032 m
Explanation:
The resistance of a wire is given by
R = ρ L / A
done ρ is the resistivity of matter, L is the length and A is the area
L = R A /ρ
the area of a circle is
A = π r² = π d² / 4
L = R π d² / 4ρ
in the problem they indicate the resistance of 240 Ω, the diameter of 0.040 mm and the resistivity of 5 10⁻⁷ Ω / m
Let's reduce the diameter to SI units
d = 0.040 mm (1 m / 1000 mm) = 4 10⁻⁵ m
let's calculate
L = 240 π (4 10⁻⁵) 2 / (4 5 10⁻⁷)
L = 6.0319 m
L = 6.032 m
