A microscope is focused on a mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?
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Question

A microscope is focused on a mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over the mark. How should the microscope be moved to get the mark in focus again?

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G1 Physics · Accepted Answer

Step 1: Apparent depth through glass t/μ instead of actual depth t. Step 2: Apparent upward shift Δ = t − t/μ = t(1 − 1/μ). Step 3: Δ = 3(1 − 1/1.5) = 3(1/3) = 1 cm. Step 4: Raise microscope by 1 cm to focus apparent position. Final answer: (B) 1 cm upward.