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प्रश्न
If there is a convex lens of focal length 75 cm and a concave lens of focal length 40 cm, then calculate their combined power and combined focal length.
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उत्तर
Power of convex lens = `100/("f"("cm"))`
= `100/75` = + 1.33 D.
Power of concave lens = `100/("f"("cm"))`
= `100/40` = − 2.5 D.
Their combined power P = + 1.33 D + (− 2.5 D)
P = − 1.17 D.
Their combined focal length F = `100/"P"=100/(-1.17)`
F = − 85.47 cm.
Negative sign indicates that the nature of their combination is concave.
संबंधित प्रश्न
State power of a lens S.I. unit.
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1) Which lenses are used in her spectacles?
2) State the defect of vision Kavita is suffering from.
3) Find the focal length of the lenses used in her spectacles
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Match the following:
| Column - I | Column - II | ||
| 1 | Retina | a | Path way of light |
| 2 | Pupil | b | Far point comes closer |
| 3 | Ciliary muscles | c | near point moves away |
| 4 | Myopia | d | Screen of the eye |
| 5 | Hypermetropia | e | Power of accommodation |
