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प्रश्न
Define the term focal length of a lens.
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उत्तर
The distance from the optical centre O of the lens to its second focal point is called the focal length of the lens.
संबंधित प्रश्न
State the power of a lens S.I. unit.
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
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:
The power of a combination of two lenses X and Y is 5 D. If the focal length of lens X be 15 cm :
(a) calculate the focal length of lens Y.
(b) state the nature of lens Y.
On reducing the focal length of a lens, its power ______.
A diverging lens of focal length 20 cm and a converging lens of focal length 30 cm are placed 15 cm apart with their principal axes coinciding. Where should an object be placed on the principal axis so that its image is formed at infinity?
Surabhi from std. X uses spectacle. The power of the lenses in her spectacle is 0.5 D.
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.
In what unit is the power of a lens expressed?
A greater numerical value of the power of a lens means:
When a lens is placed in a liquid, light refracts at:
