We need to find how long a 0.1 mm ^ 2 nickel wire is required to make a 180 Ohm rheostat.
Let’s start by writing it down:
S = 0.1mm ^ 2;
R = 180 ohms;
we also need for calculations:
pnik = 0.4 * 10 ^ -6 (Ohm * m ^ 2) / m.
We need to find the length of the wire:
Let’s remember the formula for calculating resistance:
R = pnik * l / S.
We express the length from the formula:
S * R = pnik * l;
l = S * R / pnik.
It remains to substitute the values into the formula and perform calculations:
l = (180 * 0.1 * 10 ^ -6) / (0.4 * 10 ^ -6) = 45 meters.
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