For a 20 ohm rheostat, you need to take a 5 m long nickel wire. What cross section should the wire be?

These tasks: R (calculated resistance of the rheostat) = 20 Ohm; l (length of used nickel wire) = 5 m.
Reference values: ρ (nickelin resistivity) = 0.4 Ohm * mm2 / m.
The value of the cross-sectional area of the wire is determined by the formula for calculating the resistance: R = ρ * l / S and S = ρ * l / R.
Let’s calculate: S = 0.4 * 5/20 = 0.1 mm2.
Answer: Nickel wire should have a cross-sectional area of 0.1 mm2.