Задача 30976.

The current in the solenoid varies according to the equation = 4e ^ -500t A. The length of the solenoid is 0.5 m, the area of one turn is S = 100 cm ^ 2, the number of turns is N = 1000. Find: the time for which the energy of the magnetic field of the solenoid will decrease by a factor of 10 ; The value of this energy and its bulk density after this time interval (the time is counted from the instant t = 0).

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