What cross section do you need to take a steel wire 5 km long so that its resistance is 60 Ohm?

Initial data: l (length of steel wire) = 5 km; R (required resistance of the steel wire) = 60 ohms.

Reference data: ρ (resistivity of steel) = 0.13 Ohm * mm ^ 2 / m.

SI system: l = 5 km = 5000 m.

We express the cross-section of the steel wire from the following formula: R = ρ * l / S, whence S = ρ * l / R = 0.13 * 5000/60 = 10.83 mm ^ 2.

Answer: The cross-sectional area of the steel wire should be 10.83mm ^ 2.