Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
BITSAT 2016
Exam
BITSAT
Year
2016
Subject
Physics
Chapter
Ray Optics

BITSAT 2016 · Physics · Ray Optics

A lens having focal length f and aperture of diameter d forms an...

A lens having focal length ff and aperture of diameter dd forms an image of intensity II. Aperture of diameter d2\frac{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

  1. Aff and I4\frac{I}{4}
  2. B3f4\frac{3 f}{4} and I2\frac{I}{2}
  3. Cff and 3I4\frac{3 I}{4}
  4. Df2\frac{f}{2} and I2\frac{I}{2}

Correct answer

C. ff and 3I4\frac{3 I}{4}

Step-by-step solution

Bycovering aperture, focal length does not change. But intensity is reduced by 14\frac{1}{4} times as aperture diameter d2\frac{d}{2} is covered. ∴I′=I−I4=3I4∴ New focal length =f and intensity =3I4.\begin{array}{l} \therefore \quad I^{\prime}=I⁻\frac{I}{4}=\frac{3 I}{4}\\ \therefore \quad \text{ New focal length }=\mathrm{f} \text{ and intensity }=\frac{3 I}{4}. \end{array}
Practice Ray Optics on Quantrex Academy →

More from Ray Optics

Power of biconvex lens is P diopter. When it is cut into two symmetrical halves by a… BITSAT 2024The magnifying power of a telescope is 9. When it is adjusted for parallel rays, the… BITSAT 2024In normal adjustment, for a refracting telescope, the distance between objective and eye… BITSAT 2024If the distance between object and its two times magnified virtual image produced by a… BITSAT 2024A thin prism P_1 with an angle 6^ ^ ∘ and made of glass of refractive index 1.54 is… BITSAT 2023In a reflecting telescope, a secondary mirror is used to: BITSAT 2023A mosquito O is sitting infront of a glass rod having spherical end of radius of… BITSAT 2022An achromatic convergent doublet of two lense in contact has a power of +5 D . The power… BITSAT 2022 Full Ray Optics list All BITSAT PYQs