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NEET 2008
Exam
NEET
Year
2008
Subject
Physics
Chapter
Ray Optics

NEET 2008 · Physics · Ray Optics

Two thin lenses of focal lengths f_1 and f_2 are in contact and...

Two thin lenses of focal lengths f1f_1 and f2f_2 are in contact and coaxial. The power of the combinations is

Options

  1. Af1+f2f1f2\frac{f_1+f_2}{f_1 f_2}
  2. Bf1f2\sqrt{\frac{f_1}{f_2}}
  3. Cf2f1\sqrt{\frac{f_2}{f_1}}
  4. Df1+f22\frac{f_1+f_2}{2}

Correct answer

A. f1+f2f1f2\frac{f_1+f_2}{f_1 f_2}

Step-by-step solution

1f=1f1+1f2⇒P=f1+f2f1f2\begin{aligned}& \frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}\\ \Rightarrow \quad P & =\frac{f_1+f_2}{f_1 f_2} \end{aligned}
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