What cross section do you need to take a 10 m long constantan wire to have a resistance of 50 ohms?

Initial data: l (length of constantan wire) = 10 m; R (the resistance that a constantan wire should have) = 50 ohms.

Reference data: ρ (resistivity constantan) = 0.5 Ohm * mm2 / m.

We calculate the cross section that a constantan wire should have from the formula: R = ρ * l / S, whence S = ρ * l / R.

Let’s make a calculation: S = 0.5 * 10/50 = 0.1 mm2.

Answer: You will need to take a constantan wire with a cross section of 0.1 mm2.