Câu 1:
Điện trở là:
\(R = \rho \dfrac{l}{S} = 1,{7.10^{ - 8}}.\dfrac{{10000.1000}}{{0,{{5.10}^{ - 6}}}} = 340000\Omega \)
Công suất hao phí:
\({P_{hp}} = {\left( {\dfrac{P}{U}} \right)^2}R = {\left( {\dfrac{{{{10.10}^6}}}{{{{500.10}^3}}}} \right)^2}.340000 = 136000000W\)
Câu 2:
Hình vẽ 1 + 2
Câu 3:
Hình 1
Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{8}{{OA'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' + OF'}} = \dfrac{{12}}{{OA' + 12}}\\
\Rightarrow \dfrac{8}{{OA'}} = \dfrac{{12}}{{OA' + 12}} \Rightarrow OA' = 24cm\\
\Rightarrow \dfrac{{AB}}{{A'B'}} = \dfrac{1}{3} \Rightarrow A'B' = 3cm
\end{array}\)
Câu 4:
Hình 3
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{{15}}{{OA'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' - OF'}} = \dfrac{{10}}{{OA' - 10}}\\
\Rightarrow \dfrac{{15}}{{OA'}} = \dfrac{{10}}{{OA' - 10}} \Rightarrow OA' = 30cm
\end{array}\)
