A person needs a lens of power –4.5 D for correction of her vision.
(a) What kind of defect in vision is she suffering from?
(b) What is the focal length of the corrective lens?
(c) What is the nature of the corrective lens?
a) Myopia (nearsightedness)- A person who is suffering from this eye defect cannot see the distant objects clearly. The normal vision of the eye is 25 cm. In this eye ball is longer than usual and light rays converge in front of the retina which forms the blurred image.
b) Formula, P= 1/f
In this, power of lens is given i.e. – 4.5 D and now put the value of P in this formula; then we will find Focal length of the corrective lens.
P= 1/f where, P is the power of the lens and, f is the focal length
F = 1/P = 1/ -4.5 = -0.22 m
c) Nature of the lens is Diverging lens (it spreads out light rays that have been refracted).
You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table 10.3.
| Material medium |
Refractive index |
Material medium |
Refractive index |
| Air | 1.0003 | Canada Balsam |
1.53 |
| Ice | 1.31 | ||
| Water | 1.33 | Rock salt | 1.54 |
| Alcohol | 1.36 | ||
| Kerosene | 1.44 | Carbon disulphide |
1.63 |
| Fused quartz |
1.46 | ||
| Turpentine oil |
1.47 | Ruby | 1.71 |
| Benzene | 1.50 | Sapphire | 1.77 |
| Crown glass |
1.52 | Diamond | 2.42 |
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Welcome to the NCERT Solutions for Class 10 Science - Chapter . This page offers a step-by-step solution to the specific question from Excercise 0 , Question 18: A person needs a lens of power –4.5 D for correction of her vision. (a) What kind of defect i....
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