It is necessary to make a 6.0 ohm rheostat from a nickel wire with a diameter of 0.80 mm.

It is necessary to make a 6.0 ohm rheostat from a nickel wire with a diameter of 0.80 mm. How long should you take the conductor?

Initial data: R (required resistance of the manufactured rheostat) = 6 Ohm; d (nickel conductor diameter) = 0.8 mm.

Reference data: ρ (specific resistance of nickelin at 20 ºС) = 0.4 Ohm * mm2 / m.

The required length of the nickelin conductor is determined from the formula: R = ρ * l / S = 4 * ρ * l / (Π * d ^ 2), whence l = R * Π * d ^ 2 / 4ρ.

Let’s make a calculation: l = 6 * 3.14 * 0.8 ^ 2 / (4 * 0.4) = 7.536 m.

Answer: It is necessary to take a nickeline conductor with a length of 7.536 m.