Question

7.9. Ba đoạn dây dẫn làm bằng đồng có cùng tiết diện,có chiều dài ll là l₁,l₂=2l₁,l₃=2l₂.Khi mắc nt chúng vào U 21V thì U mỗi dây dẫn là?

Answer 1

\(\Rightarrow\left\{{}\begin{matrix}\dfrac{R1}{R2}=\dfrac{l1}{l2}=\dfrac{l1}{2l1}=0,5\Rightarrow R1=0,5R2\\\dfrac{R2}{R3}=\dfrac{l2}{l3}=\dfrac{l2}{2l2}=0,5\Rightarrow R2=0,5R3\\\dfrac{R1}{R3}=\dfrac{l1}{l3}=\dfrac{l1}{2l2}=\dfrac{l1}{4l1}=0,25\Rightarrow R1=0,25R3\end{matrix}\right.\)

\(R1ntR2ntR3\Rightarrow Im=\dfrac{U}{R1+R2+R3}=\dfrac{21}{R1+\dfrac{R1}{0,5}+\dfrac{R1}{0,25}}=\dfrac{21}{\dfrac{0,5R1+R1+2R1}{0,5}}=\dfrac{10,5}{3,5R1}\left(A\right)\Rightarrow\left\{{}\begin{matrix}U1=Im.R1=\dfrac{10,5.R1}{3,5R1}=3V\\U2=Im.R2=\dfrac{10,5}{3,5R1}.\dfrac{R1}{0,5}=6V\\U3=U-U1-U2=12V\\\end{matrix}\right.\)