giải tự từ 25-30 giúp em ạ

Câu 25: C

Ta có:

\(\begin{array}{l}
\omega  = \dfrac{1}{{\sqrt {LC} }} = \dfrac{1}{{\sqrt {{{10.10}^{ - 3}}{{.4.10}^{ - 6}}} }} = 5000\left( {rad/s} \right)\\
f = \dfrac{\omega }{{2\pi }} = \dfrac{{5000}}{{2\pi }} = 795,78Hz
\end{array}\)

Câu 26: A

Ta có: 

\(\begin{array}{l}
\omega  = \dfrac{1}{{\sqrt {LC} }} = \dfrac{1}{{\sqrt {{{250.10}^{ - 3}}{{.9.10}^{ - 6}}} }} = \dfrac{{2000}}{3}\left( {rad/s} \right)\\
T = \dfrac{{2\pi }}{\omega } = \dfrac{{2\pi }}{{\dfrac{{2000}}{3}}} = 3\pi {.10^{ - 3}}\left( s \right) = 9,42ms
\end{array}\)

Câu 27: A

Ta có:

\(\begin{array}{l}
\omega  = 2\pi f = 2\pi .500 = 1000\pi \left( {rad/s} \right)\\
 \Rightarrow \dfrac{1}{{\sqrt {LC} }} = 1000\pi \\
 \Rightarrow \dfrac{1}{{\sqrt {L.\dfrac{{{{10}^{ - 4}}}}{\pi }} }} = 1000\pi \\
 \Rightarrow L = 3,{18.10^{ - 3}}\left( H \right)
\end{array}\)

Câu 28: A

Ta có: 

\(\begin{array}{l}
\omega  = 2\pi f = 2\pi .5000 = 10000\pi \left( {rad/s} \right)\\
 \Rightarrow \dfrac{1}{{\sqrt {LC} }} = 10000\pi \\
 \Rightarrow \dfrac{1}{{\sqrt {0,{{318.10}^{ - 3}}.C} }} = 10000\pi \\
 \Rightarrow C = 3,{19.10^{ - 6}}\left( F \right)
\end{array}\)

Câu 29: B

Ta có: 

\(\begin{array}{l}
\omega  = \dfrac{1}{{\sqrt {LC} }} = \dfrac{1}{{\sqrt {{{10}^{ - 6}}{{.10}^{ - 8}}} }} = {10^7}\left( {rad/s} \right)\\
f = \dfrac{\omega }{{2\pi }} = \dfrac{{{{10}^7}}}{{2\pi }} = 1,6MHz
\end{array}\)

Câu 30: A

Ta có: 

\(\begin{array}{l}
\omega  = {10^5}\pi  \Rightarrow \dfrac{1}{{\sqrt {0,{{318.10}^{ - 9}}.L} }} = {10^5}\pi \\
 \Rightarrow L = 0,0318H = 31,8mH
\end{array}\)

Câu 31: B

Ta có:

\(f = \dfrac{\omega }{{2\pi }} = \dfrac{{{{2.10}^4}.\pi }}{{2\pi }} = {10^4}Hz = 10kHz\)