Question
A point object is placed at a distance of 25 cm from a convex lens of focal length 20 cm. 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 is
Answer: Option D
:
D
Image will be formed at infinity if object is placed at focus of the lens i.e., at 20 cm from thelens. Hence,
Shift = 25−20=(1−1μ)t
or 5=(1−11.5)t
or t=5×1.50.5=15cm
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:
D
Image will be formed at infinity if object is placed at focus of the lens i.e., at 20 cm from thelens. Hence,
Shift = 25−20=(1−1μ)t
or 5=(1−11.5)t
or t=5×1.50.5=15cm
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