QuestionOptics / lens combinations
The eyepiece of a telescope is a system of two biconvex lenses L1 and L2, of focal length 30 cm and 20 cm respectively, with a separation of 2 cm between them. Lens L2 faces the eye. This eyepiece is to be replaced by a single bi-convex lens L. Which one among the following is the correct combination of the focal length (F in cm) of the lens L and its distance from the position of lens L1 (δ in cm) ?
- (a) F = 12·5 and δ = 1·17
- (b) F = 12·5 and δ = 1·15
- (c) F = 11·5 and δ = 1·17
- (d) F = 11·5 and δ = 1·15
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