Đáp án:
a) hình vẽ
b) 5
Giải thích các bước giải:
b) Ta có:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{{12}}{{OA'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' - OF'}} = \dfrac{{10}}{{OA' - 10}}\\
\Rightarrow \dfrac{{12}}{{OA'}} = \dfrac{{10}}{{OA' - 10}} \Rightarrow OA' = 60m\\
\Rightarrow \dfrac{{A'B'}}{{AB}} = 5
\end{array}\)
c) TH1: Ảnh thật
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{d}{{d'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' - OF'}} = \dfrac{f}{{d' - f}}\\
\Rightarrow \dfrac{d}{{d'}} = \dfrac{f}{{d' - f}} \Rightarrow \dfrac{1}{f} = \dfrac{1}{d} + \dfrac{1}{{d'}}
\end{array}\)
TH2: Ảnh ảo:
\(\begin{array}{l}
\dfrac{{AB}}{{A'B'}} = \dfrac{{OA}}{{OA'}} = \dfrac{d}{{d'}}\\
\dfrac{{AB}}{{A'B'}} = \dfrac{{OI}}{{A'B'}} = \dfrac{{OF'}}{{OA' + OF'}} = \dfrac{f}{{d' + f}}\\
\Rightarrow \dfrac{d}{{d'}} = \dfrac{f}{{d' + f}} \Rightarrow \dfrac{1}{f} = \dfrac{1}{d} - \dfrac{1}{{d'}}
\end{array}\)
