Welcome to the NCERT Solutions for Class 10 Science - Chapter Light - Reflection and Refraction. This page offers a step-by-step solution to the specific question from Exercise 4, Question 2: . With detailed answers and explanations for each chapter, students can strengthen their understanding and prepare confidently for exams. Ideal for CBSE and other board students, this resource will simplify your study experience.
A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
The image formed is inverted and of the same size as the object. When an object is placed at the centre of curvature, 2F1, of a convex lens, its image is formed at the centre of curvature, 2F2, on the other side of the lens.
Given,
The image of the needle is formed at a distance of 50 cm from the convex lens. Hence, the needle is placed in front of the lens at a distance of 50 cm.
Object distance, u = −50 cm
Image distance, v = 50 cm
Focal length = f
Putting values to the lens formula,
Hence, the power of the given lens is +4 D.
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 |
Find out, from Table 10.3, the medium having highest optical density. Also find the medium with lowest optical density.
| 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 |
Table 10.3 Absolute refractive index of some material media
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Read MoreWelcome to the NCERT Solutions for Class 10 Science - Chapter . This page offers a step-by-step solution to the specific question from Excercise 4 , Question 2: A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is t....
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