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A point object is placed at a distance of 25 cm from a convex lens of focal length 20cm. If a glass slab of thickness t and refractive index 1.5 is inserted between the lens and the object, the image is formed at infinity. The thickness t isA. 10cmB. 5cmC. 20cmD. 15cm |
Answer» Correct Answer - d. Image will be formed at infinity if object is placed at focus of the lens, i.e., at 20cm form the lens. Hence, shift `=25-20=(1-(1)/(mu))mu` or `5=(1-(1)/(1.5))t ` or `t=(5xx1.5)/(0.5)=15cm` |
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