MHT CET · Physics · Ray Optics
The focal length of combination of lenses formed with lenses having power of +2.50 D and -3.75 D , will be
- A -20 cm
- B -40 cm
- C -60 cm
- D -80 cm
Answer & Solution
Correct Answer
(D) -80 cm
Step-by-step Solution
Detailed explanation
\(\begin{aligned}
& P=P_1+P_2 \\
& =2.50+(-3.75) \\
& =2.50-3.75 \\
& =-1.25 \mathrm{D} \\
& \therefore \quad \mathrm{f}=\frac{1}{\mathrm{P}}=\frac{1}{-1.25}=-0.8 \mathrm{~m} \\
& \therefore \quad \mathrm{f}=-80 \mathrm{~cm}
\end{aligned}\)
& P=P_1+P_2 \\
& =2.50+(-3.75) \\
& =2.50-3.75 \\
& =-1.25 \mathrm{D} \\
& \therefore \quad \mathrm{f}=\frac{1}{\mathrm{P}}=\frac{1}{-1.25}=-0.8 \mathrm{~m} \\
& \therefore \quad \mathrm{f}=-80 \mathrm{~cm}
\end{aligned}\)
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