Bài 1:
a. \(R=p\dfrac{l}{S}\Rightarrow l=\dfrac{R\cdot S}{p}=\dfrac{10\cdot\left(\pi\dfrac{0,4^2}{4}\right)\cdot10^{-6}}{0,4\cdot10^{-6}}=3,14\left(m\right)\)
b. \(Q=A=I^2Rt\Rightarrow I=\sqrt{\dfrac{Q}{Rt}}=\sqrt{\dfrac{9000}{10\cdot5\cdot60}}=\sqrt{3}A\)