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प्रश्न
A nearsighted person cannot see beyond 25 cm. Assuming that the separation of the glass from the eye is 1 cm, find the power of lens needed to see distant objects.
उत्तर
Given:
As the person wears spectacles at a distance of 1 cm from the eyes.
Distance of the image from the glass, v = Distance of the image from the eye − Separation between the glass and the eye
v = 25 − 1 = 24 cm = 0.24 m
For the near-sighted person, u = ∞.
The lens formula is given by
`1/v -1/u = 1/f`
On substituting the values in the above formula, we get:
`1/f = 1/((-0.24))-1/∞ = -42`
Power of the lens, P = `1/f` = − 4.2 D
Thus, the power of the lens required to see distant objects is − 4.2 D.
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संबंधित प्रश्न
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A man wearing glasses of focal length +1 m cannot clearly see beyond 1 m
When we see an object, the image formed on the retina is
(a) real
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(c) erect
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(a) If the far point goes ahead, the power of the divergent lens should be reduced.
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A person looks at different trees in an open space with the following details. Arrange the trees in decreasing order of their apparent sizes.
| Tree | Height(m) | Distance from the eye(m) |
| A | 2.0 | 50 |
| B | 2.5 | 80 |
| C | 1.8 | 70 |
| D | 2.8 | 100 |
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