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प्रश्न
What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:
(a) the electric bulb
(b) a piece of white paper
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उत्तर
We cannot see anything in a dark room as there is no light present.
(a) We see the electric bulb because it produces light that reaches our eyes directly.
(b) We see a piece of white paper due to the diffused reflection of light from the surface of the paper.
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संबंधित प्रश्न
What is meant by a power of a lens? Define its SI unit.
How unit of power related to focal length of a lens?
Find the power of a concave lens of focal length 2m.
What is the focal length of a convex lens of focal length 30 cm in contact with a concave lens of focal length 20 cm? Is the system a converging or a diverging lens? Ignore thickness of the lenses.
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
The lens A has a focal length of 25 cm whereas another lens B has a focal length of 60 cm. Giving reason state, which lens has more power: A or B.
Which type of lens has (a) a positive power, and (b) a negative power?
Which of the two has a greater power: a lens of short focal length or a lens of large focal length?
Which has more power : a thick convex lens or a thin convex lens, made of the same glass? Give reason for your choice.
What is the nature of a lens having a power of + 0.5 D?
Fill in the following blank with suitable word:
For converging lenses, the power is __________ while for diverging lenses, the power is ___________.
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On reducing the focal length of a lens, its power ______.
A double convex lens has two surfaces of equal radii R and refractive index \[m = 1 \cdot 5\]
A stick partly immersed in water appears to be bent. Draw a ray diagram to show the bending of the stick when placed in water and viewed obliquely from above.
Complete the diagram to show the formation of the image of the object AB.
(i) Name the Lens LL’.
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(iii) State three characteristics of the image.
If focal length of a convex lens is 20 cm at what is the power of the lens?
When monochromatic red light is used instead of blue light in a convex lens, its focal length will ______.
The power of convex lens of focal length 20 cm is ______.
