How long would a nickel wire with a cross-sectional area of 0.1 mm ^ 2

How long would a nickel wire with a cross-sectional area of 0.1 mm ^ 2 be required to make a rheostat with a maximum resistance of 180 ohms?

Initial data: S (cross-sectional area of nickel wire) = 0.1 mm2; R (maximum resistance of the manufactured rheostat) = 180 ohms.

Reference data: ρ (specific resistance of nickelin) = 0.4 Ohm * mm2 / m.

We calculate the required length of nickel wire from the formula for calculating the resistance: R = ρ * l / S, whence l = R * S / ρ.

Let’s make the calculation: l = 180 * 0.1 / 0.4 = 45 m.

Answer: To manufacture a rheostat, you need a 45 meter long nickelin wire.