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A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperature of diameter d/2 in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively:
Options
(a) f and I/4
(b) 3f/4 and I/2
(c) f and 3I/4
(d) f/2 and I/2
Correct Answer:
f and 3I/4
Explanation:
By covering aperture, focal length does not change. But intensity is reduced by 1/4 times, as aperture diameter d/2 is covered.
I’ = I – I / 4 = 3I / 4
New focal length = f and intensity = 3I / 4
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Topics: Ray Optics
(94)
Subject: Physics
(2479)
Important MCQs Based on Medical Entrance Examinations To Improve Your NEET Score
- A milli ammeter of range 10 mA has a coil of resistance 1 ohm
- A solid sylinder of mass 3 kg is rolling on a horizontal surface with velocity 4 ms⁻¹
- The amplitude of S.H.M. y=2 (sin 5πt+√2 cos 5πt) is
- A solid which is transparent to visible light and whose conductivity increases
- A person can see clearly objects only when they lie between 50 cm and 400 cm from
Topics: Ray Optics (94)
Subject: Physics (2479)
Important MCQs Based on Medical Entrance Examinations To Improve Your NEET Score
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