The electronic tube current flows from the cylinder to the metal filament disposed axially therein. Determine the current density near the filament and adjacent to the cylinder under the following conditions: current is 3 mA, the length of the thread in the cylinder 2.5 cm, 0.02 mm diameter filament, the diameter of the cylinder of 1 cm.

Detailed solution shorthand terms, formulas and laws used in the decision, the withdrawal of the calculation formula and the response.
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