Answer / 7anoter4

Magnetic energy is W=B*H =miuo*H^2=K*i^2
Wmax=K*Imax^2 ¼*Wmax=K*Imax^2/4 i=Imax/2
The current equation it is: i=Imax*[1-e^(-t*L/R)] . If
i=1/2*Imax then : e^(-t*L/R)=1/2 and t=-LN(1/2)*R/L R=10
ohm L=0.250 H t=27.73 sec.

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