Лаг1989 задача №15.1

A nickel band of thickness a = 0.2 mm and width b = 3 mm must be made of a rheostat with resistance R = 2.5 Ohm. How long is L need to take a tape and what maximum voltage U can be applied to this rheostat, if the permissible current density for nickel is j = 0.2 A / mm²?

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