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प्रश्न
Find the power of a convex lens of focal length of + 25 cm.
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उत्तर
Given: Focal length (f) = 25 cm = 0.25 m
To find: Power of the lens (P)
Formula: P = `1/("f"("m"))`
Calculation: From formula, P = `1/0.25` = 4 D
The power of the convex lens is 4 D.
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संबंधित प्रश्न
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(b) What is the magnification in this case?
(c) Is the magnification equal to the magnifying power in this case? Explain.
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Kavita from 10th is using spectacles. The power of the lenses in her spectacles is –2.5 dioptre. Answer the following questions:
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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(a) the electric bulb
(b) a piece of white paper
Which type of lens has (a) a positive power, and (b) a negative power?
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Fill in the following blank with suitable words :
The reciprocal of the focal length in metres gives you the _________ of the lens, which is measured in ___________.
Two lenses A and B have focal lengths of +20 cm and, −10 cm, respectively.
(a) What is the nature of lens A and lens B?
(b) What is the power of lens A and lens B?
(c) What is the power of combination if lenses A and B are held close together?
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Answer the following questions from the given information:
- Identify the type of lenses used in her spectacle.
- Identify the defect of vision Surabhi is suffering from.
- Find the focal length of the lenses used in her spectacle.
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| 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 |
Assertion and reasoning type
- Assertion: Myopia is due to the increase in the converging power of eye lens.
- Reason: Myopia can be corrected with the help of concave lens.
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