Ln object is placed at a distance of 12 cm from a anvex lens on its principal axis and a virtual image f certain size is formed. If the object is moved further cm away from the lens, a real image of the same ize as that of the virtual image is formed. Whi

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Q: 77 (NDA-II/2009)
Ln object is placed at a distance of 12 cm from a anvex lens on its principal axis and a virtual image f certain size is formed. If the object is moved further cm away from the lens, a real image of the same ize as that of the virtual image is formed. Which ne of the following is the focal length of the lens?

question_subject: 

Maths

question_exam: 

NDA-II

stats: 

0,2,9,2,2,3,4

keywords: 

{'focal length': [1, 0, 5, 7], 'anvex lens': [0, 0, 1, 0], 'lens': [0, 0, 0, 1], 'ln object': [0, 0, 1, 0], 'virtual image': [0, 0, 1, 1], 'distance': [0, 3, 3, 3], 'real image': [0, 0, 0, 1], 'object': [1, 0, 11, 43], 'principal axis': [0, 0, 1, 1], 'cm': [2, 0, 7, 20], 'certain size': [0, 0, 1, 0]}

In this question, we are given that an object is placed at a distance of 12 cm from a convex lens on its principal axis. We are also told that a virtual image of a certain size is formed.

When the object is moved further away from the lens, we observe that a real image of the same size as the virtual image is formed.

Based on this information, we can conclude that the object is being placed between the lens and its focal point. This is because when an object is placed between the lens and its focal point, a virtual image of a certain size is formed.

However, when the object is moved further away from the lens, beyond the focal point, a real image of the same size as the virtual image is formed.

From this, we can deduce that the focal length of the lens must be greater than 12 cm, but less than the distance at which the object is moved.

Among the given options, option 2, which is 16 cm, satisfies this condition. Therefore, the correct answer is option 2.

Alert - correct answer should be 14 cm.