i(t) = 40sin(60pitheta-pi)

Question

t represents time, what is the least amount of time used for 20 amperes? 

Answer 1

i(t)=-40 = i(theta) find theta=t

40sin(7pi/2 -pi) = 40sin(5pi/2) =-40 at

as 60pit= 5pi/2 so t=120/5= 24 seconds to reach minimum -40

40sin(60pi(24) -pi) = 40sin(144pi-pi)= 40sin143pi = 40sin((1,5)pi) =40(-1)=-40