A lens is a transparent medium bounded by two surfaces, with one or both surfaces being…
Physics · Class 12 · CBSE — Ray Optics & Optical Instruments
A lens is a transparent medium bounded by two surfaces, with one or both surfaces being spherical. The focal length of a lens is determined by the radii of curvature of its two surfaces and the refractive index of its medium with respect to that of the surrounding medium. The power of a lens is reciprocal of its focal length. If a number of lenses are kept in contact, the power of the combination is the algebraic sum of the powers of the individual lenses.
Two convex lenses of focal lengths 60 cm and 20 cm are held coaxially in contact with each other. The power of the combination is:
- 6.6 D
- 15 D
- \(\frac{1}{15}\) D
- \(\frac{1}{80}\) D
Answer
(A) 6.6 D
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