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प्रश्न
Name the type of lens whose power is positive.
The image of an object formed by a lens is real, inverted and of the same size as the object. If the image is at a distance of 40 cm from the lens, what is the nature and power of the lens ? Draw ray diagram to justify your answer.
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उत्तर
The power of a convex lens is positive.
It is given that the image of the object formed by the lens is real, inverted and of the same size as the object. Also, we know that only convex lens can form a real and inverted image. Thus, the given lens is a convex lens. In the given case, the object is placed at 2F1 and the image is formed at 2F2.
It is clear from the figure that the focal length of the lens (f) is 40 cm.
Now, power (P) is given by
\[P = \frac{1}{f}\]
\[\Rightarrow P = \frac{1}{20 \times {10}^{- 2} m}\]
\[ \Rightarrow P = + 5 D\]
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संबंधित प्रश्न
Define 1 dioptre of power of a lens.
Consider two statements A and B given below:
A: real image is always inverted
B: virtual image is always erect
Out of these two statements:
Name the physical quantity whose unit is dioptre.
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What is the nature of a lens having a power of + 0.5 D?
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Consider the situation described in the previous problem. Where should a point source be placed on the principal axis so that the two images form at the same place?
Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?
A point object is placed at O in front of a glass sphere as shown in figure.
Show the formation of the image by the sphere.
In what unit is the power of a lens expressed?
