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

December 30, 2020 | education

| 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.

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