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Using the displacement method, a convex lens placed between a fixed…
Question
Using the displacement method, a convex lens placed between a fixed object and a screen 100 cm apart forms a sharp image at two distinct lens positions. The two positions are separated by 40 cm. Find the focal length of the lens in cm.
✓ Verified answer: 21checked by our engine — not a guess
Step-by-step solution
In the displacement method, f = (D^2 - d^2)/(4D), where D is the object-screen distance and d is the separation between the two lens positions.
f = (100^2 - 40^2)/(400) = (10000 - 1600)/400 = 8400/400 = 21 cm.
Final answer21
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