Intensity, I∝A2 ⇒I1I2=[ A1A2]2=πr2πr2−4πr2=43 ⇒I2=43I1 and focal length remains unchanged.
A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperture of diameter 2d in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively
Held on 30 Apr 2010 · Verified 9 Jul 2026.
f and 41
43f and 2I
f and 43I
2f and 2I
Sign in to track your attempts and accuracy.
Sign in to keep a private note on this question. Nothing you write is ever public.
The refractive index of glass is 1.5. The speed of light in glass is:
Two thin lenses of focal lengths f₁ = +20 cm and f₂ = -10 cm are in contact. The power of the combination is:
In a certain camera, a combination of four similar thin convex lenses are arranged axially in contact. Then the power of the combination and the total magnification in comparison to the power $(p)$ and magnification $(m)$ for each lens will be, respectively
The intensity of transmitted light when a polaroid sheet, placed between two crossed polaroids at $22.5^{\circ}$ from the polarization axis of one of the polaroid, is ( $\mathrm{I}_0$ is the intensity of polarised light after passing through the first polaroid):
A microscope has an objective of focal length 2 cm , eyepiece of focal length 4 cm and the tube length of 40 cm . If the distance of distinct vision of eye is 25 cm , the magnification in the microscope is :
Work through every NEET UG Optics PYQ, year by year.