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A converging beam of rays is incident on a diverging lens. Having passed through the lens the rays intersect at a point 15 cm from the lens on the opposite side. If the lens is removed the point where the rays meet will move 5 cm closer to the lens. The focal length of the lens is
-
- – 10 cm
- 20 cm
- –30 cm
- 5 cm
Correct Option: C
By lens formula,
| - | = | ||||
| v | u | f |
u = 10 cm
v = 15 cm
f = ?
Putting the values, we get
| - | = | ||||
| 15 | 10 | f |
| = | ||||
| 150 | f |
| ∴ f = - | = -30 cm | |
| 3 |
