Question

Answer 1

Đổi: \(0,4mm^2=4.10^{-7}m^2\)

\(\rho_1=\rho_2\\ \Leftrightarrow\dfrac{R_1S_1}{l_1}=\dfrac{R_2S_2}{l_2}\\ \Leftrightarrow R_1S_1l_2=R_2S_2l_1\\ \Leftrightarrow S_2=\dfrac{R_1S_1l_2}{R_2l_1}=\dfrac{60.4.10^{-7}.30}{30.150}=1,6.10^{-7}\left(mm^2\right)\)

Answer 2

\(l_1=l_2\\ \Leftrightarrow\dfrac{R_1S_1}{\rho}=\dfrac{R_2S_2}{\rho}\\ \Leftrightarrow R_1S_1=R_2S_2\\ \Leftrightarrow S_2=\dfrac{R_1S_1}{R_2}=\dfrac{8,5.0,5}{127,5}=\dfrac{1}{30}\left(mm^2\right)\)