MHT CET · Physics · Ray Optics
Two lenses of power \(-15 \mathrm{D}\) and \(+5 \mathrm{D}\) are in contact with each other. The focal length of the combination is
- A \(-0.1 \mathrm{~cm}\)
- B \(-10 \mathrm{~cm}\)
- C \(-20 \mathrm{~cm}\)
- D \(+10 \mathrm{~cm}\)
Answer & Solution
Correct Answer
(B) \(-10 \mathrm{~cm}\)
Step-by-step Solution
Detailed explanation
\(P=\frac{1}{f}\)
For combination of lenses,
\(\mathrm{P}=\mathrm{P}_1+\mathrm{P}_2\)
Given: \(P_1=-15 \mathrm{D}\) and \(P_2=+5 F\)
\(\begin{array}{ll}
\therefore \quad & P=-10 D \\
& \Rightarrow f=-\frac{1}{10} \mathrm{~m} \\
\therefore \quad & f=-10 \mathrm{~cm}
\end{array}\)
For combination of lenses,
\(\mathrm{P}=\mathrm{P}_1+\mathrm{P}_2\)
Given: \(P_1=-15 \mathrm{D}\) and \(P_2=+5 F\)
\(\begin{array}{ll}
\therefore \quad & P=-10 D \\
& \Rightarrow f=-\frac{1}{10} \mathrm{~m} \\
\therefore \quad & f=-10 \mathrm{~cm}
\end{array}\)
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