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Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of
20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filled
with oil of refractive index 1.7. The focal length of the combination is :
  • a)
    50 cm
  • b)
    -20 cm
  • c)
    -25 cm
  • d)
    -50 cm
Correct answer is option 'D'. Can you explain this answer?
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Given data:
- Refractive index of glass lenses (n1) = 1.5
- Radius of curvature of each lens (R) = 20 cm
- Refractive index of oil (n2) = 1.7

Formula to calculate the focal length of the combination:
1/f = (n2/n1 - 1)(1/R1 - 1/R2)

Calculation:
- Since the lenses are identical, both have the same radius of curvature (R1 = R2 = 20 cm).
- Substitute the given values into the formula:
1/f = (1.7/1.5 - 1)(1/20 - 1/20)
1/f = (0.2)(0)
1/f = 0

Conclusion:
- The focal length of the combination is 0, which indicates that the light rays passing through the lenses will be parallel to the optical axis after refraction.
- This means that the focal length of the combination is at infinity or practically very far away from the lenses.
- Therefore, the correct answer is option D) -50 cm.
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Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filledwith oil of refractive index 1.7. The focal length of the combination is :a)50 cmb)-20 cmc)-25 cmd)-50 cmCorrect answer is option 'D'. Can you explain this answer?
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Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filledwith oil of refractive index 1.7. The focal length of the combination is :a)50 cmb)-20 cmc)-25 cmd)-50 cmCorrect answer is option 'D'. Can you explain this answer? for NEET 2024 is part of NEET preparation. The Question and answers have been prepared according to the NEET exam syllabus. Information about Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filledwith oil of refractive index 1.7. The focal length of the combination is :a)50 cmb)-20 cmc)-25 cmd)-50 cmCorrect answer is option 'D'. Can you explain this answer? covers all topics & solutions for NEET 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Two identical thin plano-convex glass lenses (refractive index 1.5) each having radius of curvature of20 cm are placed with their convex surfaces in contact at the centre. The intervening space is filledwith oil of refractive index 1.7. The focal length of the combination is :a)50 cmb)-20 cmc)-25 cmd)-50 cmCorrect answer is option 'D'. Can you explain this answer?.
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