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प्रश्न
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
उत्तर
The person is suffering from an eye defect called myopia. In this defect, the image is formed in front of the retina. Hence, a concave lens is used to correct this defect of vision.
Object distance, u = infinity = ∞
Image distance, v = – 80 cm
Focal length = f
According to the lens formula,
`1/"v" - 1/"u" = 1/"f"`
`1/(-80) - 1/(-∞) = 1/"f"`
`1/(-80) = 1/"f"`
f = −80 cm = −0.80 m ...(concave lens)
∴ power of modified lens,
P = `1/"f"`
= `1/(-0.80 "m")`
= −1.25 D
A concave lens of power −1.25 D is required by the person to correct his defect.
संबंधित प्रश्न
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Observe the figure and answer the following questions:
- Name the defect of vision represented in the above figure.
- State the reasons for this defect.
- How is it corrected?
- Draw the diagram to show the correction of this defect.
Complete the following table by observing the given figures:
| Figure → |  |
 |
| Points ↓ | ||
| (a) Name of the defect | ______ | ______ |
| (b) Position of the image | ______ | ______ |
| (c) Lens used to correct the defect | ______ | ______ |
