-
A plano convex lens fits exactly into a plano concave lens. Their plane surfaces are parallel to each other. If lenses are made of different materials of refractive indices µ1 and µ2 and R is the radius of curvature of the curved surface of the lenses, then the focal length of the combination is
-
-
R 2(µ1 - µ2) -
R (µ1 - µ2) -
2R (µ2 - µ1) -
R 2(µ1 + µ2)
-
Correct Option: B
| = | + | ||||
| f | f1 | f2 |
| = (μ1 - 1) |  | - |  | + (μ2 - 1) | | - | | ||||
| ∞ | -R | ∞ | R |
| = | - | ⇒ | = | ||||
| R | R | f | R |
| ⇒ f = | ||
| μ1 - μ2 |
| Hence, focal length of the combination is | ||
| μ1 - μ2 |
