F = B * I * L * sina
R = ρ*L/S => L = R*S/ρ
I = U/R
F = (B*U*R*S*sina)/(ρ*R)
F*ρ = B*U*S*sina
S = (F*ρ)/(B*U*sina)
S = (5*0,017)/(0,01*8,5*1) = 1 (мм в квадрате)