A thin lens has focal length f, and its aperture has diameter d. It forms an image of intensity

Name: Problem 2882, Chapter 35: JEE Physics
Uploaded: 2021-10-07T18:11:36-08:00
Duration: 2 min 18 s
Channel: Prem Bijarniya
Description: A thin lens has focal length f, and its aperture has diameter d. It forms an image of intensity I. Now, the central part of the aperture upto diameter (d / 2) is blocked by an opaque paper. The focal length and image intensity will change to …(A) f and (3 I / 4) (B) (3 f / 4) and (I / 2) (C) f and (I / 4) (D) (f / 2) and (I / 2)

step 1 according to question due to blocking of central part focal length does not change but intensity

Question

A thin lens has focal length $\mathrm{f}$, and its aperture has diameter d. It forms an image of intensity I. Now, the central part of the aperture upto diameter $(\mathrm{d} / 2)$ is blocked by an opaque paper. The focal length and image intensity will change to $\ldots$ (A) $\mathrm{f}$ and $(3 \mathrm{I} / 4)$ (B) $(3 \mathrm{f} / 4)$ and $(\mathrm{I} / 2)$ (C) $\mathrm{f}$ and $(\mathrm{I} / 4)$ (D) $(\mathrm{f} / 2)$ and $(\mathrm{I} / 2)$

   A thin lens has focal length $\mathrm{f}$, and its aperture has diameter
d. It forms an image of intensity I. Now, the central part of the aperture upto diameter $(\mathrm{d} / 2)$ is blocked by an opaque paper. The focal length and image intensity will change to $\ldots$
(A) $\mathrm{f}$ and $(3 \mathrm{I} / 4)$
(B) $(3 \mathrm{f} / 4)$ and $(\mathrm{I} / 2)$
(C) $\mathrm{f}$ and $(\mathrm{I} / 4)$
(D) $(\mathrm{f} / 2)$ and $(\mathrm{I} / 2)$

JEE Physics

StemEZ 1st Edition

Chapter 35, Problem 2882

Instant Answer

Solved by Expert Prem Bijarniya

10/07/2021

Step 1

Blocking part of the aperture does not change these properties, so the focal length remains the same, $\mathrm{f}$. Show more…

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A thin lens has focal length $\mathrm{f}$, and its aperture has diameter d. It forms an image of intensity I. Now, the central part of the aperture upto diameter $(\mathrm{d} / 2)$ is blocked by an opaque paper. The focal length and image intensity will change to $\ldots$ (A) $\mathrm{f}$ and $(3 \mathrm{I} / 4)$ (B) $(3 \mathrm{f} / 4)$ and $(\mathrm{I} / 2)$ (C) $\mathrm{f}$ and $(\mathrm{I} / 4)$ (D) $(\mathrm{f} / 2)$ and $(\mathrm{I} / 2)$

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Key Concepts

Aperture Area and Image Intensity

The aperture controls the amount of light that passes through the lens, which in turn affects the brightness or intensity of the image. When a part of the aperture is blocked, the effective area that gathers light is reduced, leading to a proportional decrease in the image intensity. Understanding the relationship between the area of the aperture and the light intensity is crucial to predicting how such modifications impact image brightness.

Thin Lens Focal Length

The focal length of a thin lens is determined solely by its lens properties (curvatures and refractive index) and is independent of the size or design of the aperture. Therefore, blocking part of the aperture, as long as the lens itself remains unchanged, does not affect the focal length.

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