Question

Answer 1

Bài 10.

\(R=\rho\cdot\dfrac{l}{S}=2,8\cdot10^{-8}\cdot\dfrac{10}{\pi\cdot\left(\dfrac{0,3\cdot10^{-3}}{2}\right)^2}=3,96\Omega\approx4\Omega\)

Chọn A

Answer 2

Bài 11.

\(R=\rho\cdot\dfrac{l}{S}\)

\(\Rightarrow S=\rho\cdot\dfrac{l}{R}=0,4\cdot10^{-6}\cdot\dfrac{3}{4}=3\cdot10^{-7}m^2\)

Mà \(S=\pi\cdot\dfrac{d^2}{4}\Rightarrow d=\sqrt{\dfrac{4S}{\pi}}=\sqrt{\dfrac{4\cdot3\cdot10^{-7}}{\pi}}=6,18\cdot10^{-4}m\approx0,6mm\)Chọn A