What will be the position of the object, when a convex lens of focal length 20 cm, is used to form an erect image which is twice as large as the object.
Correct answer: A. 10 cm
- A. 10 cm
- B. 20 cm
- C. 30 cm
- D. 40 cm
Explanation
This is the correct answer. To form an erect image twice as large as the object using a convex lens, the object must be placed between the focal point and the optical center of the lens. Focal length (f): 20 cm Magnification (m): 2 (since the image is twice as large as the object)Using the lens formula:1/v - 1/u = 1/fWhere: v is the image distance u is the object distanceSince the magnification is positive for an erect image:m = v/u = 2Therefore: v = 2uSubstituting this into the lens formula: 1/(2u) - 1/u = 1/20 cmSolving for u:u = 10 cmTherefore, the object must be placed 10 cm from the lens to form an erect image twice as large as the object.
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