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Physics - Geometrical Optics Question with Solution | TestHub

PhysicsGeometrical OpticsRefraction at curved surface/LensEasy2 minPYQ_2020

PhysicsEasysingle choice

A thin lens has a focal length $f_{1}$ and its aperture has a diameter $d$ . If forms an image of intensity $I$ . Now, the central part of the aperture up to diameter $\frac{d}{2}$ is blocked by an opaque paper. The focal length and image intensity will change to

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Answer:

Solution:

The focal length of the lens remains unchanged by changing its aperture.
The intensity of the image is proportional to the uncovered area.

$\frac{I_{f}}{I_{i}} = \frac{A_{f}}{A_{i}} = \frac{\frac{π}{4} [d^{2} - \frac{d^{2}}{4}]}{\frac{π}{4} d^{2}} = \frac{3}{4}$

$I_{f} = \frac{3}{4} I_{i} = \frac{3}{4} I$

Stream:NTA_ABHYAS_NEETSubject:PhysicsTopic:Geometrical OpticsSubtopic:Refraction at curved surface/Lens

⏱ 2mℹ️ Source: PYQ_2020

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