JEE Main · 2024 · 27 Jan 2024 · Shift 1 · Modern Physics

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A convex lens of focal length 40 cm forms an image of an extended source of light on a photoelectric cell. A current I is produced. The lens is replaced by another convex lens having the same diameter but focal length 20 cm. The photoelectric current now is :

(A) $\frac{I}{2}$
(B)4 I
(C)2 I
(D)I✓ Correct

Answer: (D)

Solution

The photoelectric current depends on the total light power collected by the lens, which is set by its aperture (diameter), not its focal length. Since both lenses share the same diameter, they collect the same light flux from the source; only the image size changes. The current stays

I

JEE Main · 2024 · 27 Jan 2024 · Shift 1 · Single correct option

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