Question
Download Solution PDFFind the focal length of a convex lens of focal length 50 cm in contact with a concave lens of focal length 40 cm? Also find the correct lens system?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFConcept:
- The focal length of a combination of lenses is calculated by:
\(\frac{1}{f} = \frac{1}{f_1} +\frac{1}{f_2}\)
Calculation:
Given f1 = + 50 cm (For convex lens) and f2 = - 40cm (For concave lens)
\(\frac{1}{f} = \frac{1}{50} + \frac{1}{-40}\)
\( ⇒\frac{1}{f} = \frac{4-5}{200}\)
\( ⇒ \frac{1}{f} = -\frac{1}{200}\)
⇒ \(f = - 200\ cm\)
- Since focal length is negative therefore the combination of the lens is a diverging lens of 200 cm focal length.
Additional Information
Power is reciprocal to focal length.
\(P = \frac{1}{f}\)
Last updated on May 26, 2025
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