MHT CET202611 April 2026Evening ShiftPhysicsWave OpticsActual
Converging lens of telescope 5 cm in diameter has focal length 25 cm. In the focal plane of the lens the distance between the centres of the Fraunhofer diffraction pattern is (wavelength of light used = 5000 Å, Rayleigh's criterion is satisfied)
Options
- A25000 Å
- B28000 Å
- C30500 Å
- D32000 Å
Correct answer
C. 30500 Å
Step-by-step solution
According to Rayleigh's criterion, the angular separation between two point sources just resolved by a telescope is given by = 1.22 D , where is the wavelength of light and D is the diameter of the objective lens. The linear distance x between the centres of their diffraction patterns in the focal plane of the lens is given by: x = f = 1.22 f D Given: D = 5 cm f = 25 cm = 5000 Substituting the given values: x = 1.22 5000 25 cm 5 cm x = 1.22 5000 5 x = 6.1 5000 x = 30500 Answer: 30500 Å