A converging lens of focal length f is split along its principal axis into two semicircular halves and the halves are separated by 1 mm perpendicular to the axis. The resulting system, for a small object on the axis, behaves as
A{'text': 'one image, with intensity halved', 'label': 'A'}
B{'text': 'two real images displaced perpendicular to the axis', 'label': 'B'}
C{'text': 'no image at all', 'label': 'C'}
D{'text': 'an image with the same magnification but on the optical centre', 'label': 'D'}
Answer & Solution
Correct answer: B. {'text': 'two real images displaced perpendicular to the axis', 'label': 'B'}
1. Each semicircular half acts as an independent thin lens whose optical centre is offset from the original axis.
2. Each half forms a real image of the on-axis object; the two images are displaced equal-and-opposite perpendicular to the axis.
3. This is the classical 'Billet split-lens' arrangement used as an interferometer demonstration.
_Source: NCERT Class 12 Physics Part II, Ch 9 §9.5.2 (extends to split-lens setup discussed in NCERT exercise)_
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