\(R=\rho\dfrac{l}{S}\Rightarrow S=\dfrac{\rho.l}{R}=\dfrac{0,4.10^{-6}.15}{5}=1,2.10^{-6}\left(m^2\right)\)

Bạn tự làm tóm tắt nhé!

R = p(l : S) => l = (R.S) : p

a. Chiều dài dây dẫn: l = (R.S) : p = (20.1,2.10^-6) : 3.10^-7 = 80 (m)

b. Chièu dài dây dẫn: l = (R.S) : p = (3,4.8.10^-7) : 1,7.10^-8 = 160 (m)

\(R=p\dfrac{l}{S}\Rightarrow l=\dfrac{R.S}{p}=\dfrac{10,2\cdot0,8\cdot10^{-6}}{1,7.10^{-8}}=480\left(m\right)\)

a. \(R=p\dfrac{l}{S}=0,4.10^{-6}\dfrac{15}{1.10^{-6}}=6\Omega\)

b. \(U=U1=U2=12V\)(R1//R2)

\(\Rightarrow\left\{{}\begin{matrix}I1=U1:R1=12:6=2A\\I2=U2:R2=12:12=1A\end{matrix}\right.\)

c. \(I'=I12=I3=1A\left(R12ntR3\right)\)

\(U12=I12.R12=1.\left(\dfrac{6.12}{6+12}\right)=4V\)

\(\Rightarrow U3=U-U12=12-4=8V\)

\(\Rightarrow R3=U3:I3=8:1=8\Omega\)

Ta có:

Chiều dài sợi dây:

\(l=\dfrac{Rs}{\text{ρ}}=\dfrac{15.\dfrac{0,1}{1000000}}{0,4.10^{-6}}=\dfrac{15}{4}\left(m\right)\)

\(R=p\dfrac{l}{S}\Rightarrow S=\dfrac{p\cdot l}{R}=\dfrac{0,4\cdot10^{-6}\cdot5}{10}=2\cdot10^{-7}\left(m^2\right)=0,2\left(mm^2\right)\)

\(S=\pi\dfrac{d^2}{4}\Rightarrow d=\sqrt{\dfrac{4S}{\pi}}=\sqrt{\dfrac{4\cdot0,2}{\pi}}\approx0,51\left(mm\right)\)

\(R=\dfrac{U}{I}=\dfrac{220}{2}=110\left(\Omega\right)\)

\(R=\rho\dfrac{l}{S}\Rightarrow S=\dfrac{\rho.l}{R}=\dfrac{0,4.10^{-6}.5,5}{110}=2.10^{-8}\left(m^2\right)\)

\(R=\rho\dfrac{l}{S}=0,1.10^{-6}.\dfrac{30}{0,03.10^{-6}}=100\left(\Omega\right)\)

\(R=p\dfrac{l}{S}=0,1.10^{-6}\dfrac{30}{0,03.10^{-6}}=100\left(\Omega\right)\)

a)Điện trở của dây: \(R=\dfrac{U}{I}=\dfrac{220}{2}=110\Omega\)

b)Tiết diện dây: 

\(R=\rho\cdot\dfrac{l}{S}=0,4\cdot10^{-6}\cdot\dfrac{0,5}{S}=110\)

\(\Rightarrow S=1,82\cdot10^{-9}m^2=0,182mm^2\)