JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
A thin convex lens and a thin concave lens are kept in contact and are co-axial. Which of the following statements is correct for this combination of two lenses ?
- A behaves as concave lens if \(|f_{\text{convex}}| > |f_{\text{concave}}|\)
- B behaves as concave lens if \(|f_{\text{convex}}| < |f_{\text{concave}}|\)
- C behaves as convex lens if \(|f_{\text{convex}}| > |f_{\text{concave}}|\)
- D Focal length of the lens system will change if the positions of two lenses are interchanged
Answer & Solution
Correct Answer
(A) behaves as concave lens if \(|f_{\text{convex}}| > |f_{\text{concave}}|\)
Step-by-step Solution
Detailed explanation
The equivalent focal length \(F\) of two thin lenses in contact is given by \(\dfrac{1}{F} = \dfrac{1}{f_1} + \dfrac{1}{f_2}\) For a convex lens, the focal length is positive, so \(f_1 = |f_{\text{convex}}|\) For a concave lens, the focal length is negative, so…
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