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Standard XII

Physics

Image in Thin Lens by Ray Tracing

A point objec...

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

10 cm

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5 cm

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20 cm

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15 cm

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Solution

The correct option is D 15 cm
Image will be formed at infinity if object is placed at focus of the lens i.e., at 20 cm from thelens. Hence,
Shift = $25 - 20 = (1 - \frac{1}{μ}) t$
or $5 = (1 - \frac{1}{1.5}) t$
or $t = \frac{5 \times 1.5}{0.5} = 15 c m$

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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

The correct option is D 15 cmImage 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=15 cm

The correct option is D 15 cm
Image will be formed at infinity if object is placed at focus of the lens i.e., at 20 cm from thelens. Hence,
Shift = $25 - 20 = (1 - \frac{1}{μ}) t$
or $5 = (1 - \frac{1}{1.5}) t$
or $t = \frac{5 \times 1.5}{0.5} = 15 c m$