Before You Begin
Question #43738
The Question
A uniform cylindrical telescope of mass and length is suspended vertically from a frictionless pivot at its upper end in a uniform gravitational field . The telescope has an objective lens of diameter and observes light of wavelength . A horizontal impulse is applied to the lower end of the telescope, causing it to oscillate as a physical pendulum. A long-exposure photograph of a distant binary star system is taken. Due to the oscillation, the time-averaged image of each star is broadened into a line segment. Assume the effective angular width of a single star's image is , where is the peak-to-peak angular sweep of the telescope's optical axis, and is the static Rayleigh resolution limit. The binary stars are considered just resolved when their actual angular separation equals . Calculate the minimum angular separation required to resolve the binary star system.
Options
- A.
- B.
- C.
- D.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Intuition_Breaker
Train your brain to resist "obvious" answers that are designed to deceive your intuition.
Concepts Behind This Question
Angular Resolution Limit|Physical Pendulum Inertia|Small Angle Approximation
Why This Question Is Tricky
Common Mistakes
This question tests the synthesis of rigid body dynamics (physical pendulum) with wave optics (Rayleigh criterion).
The primary trap lies in the 'Oscillatory Aperture Modulation' concept: students often fail to recognize that the motion blur of an oscillating system spans the peak-to-peak amplitude (), not just the single-sided amplitude ().
Additionally, students may incorrectly calculate the moment of inertia by using the center-of-mass formula () instead of the parallel axis theorem for a pivot at the end (), or they may incorrectly add the linear motion blur and diffraction limits in quadrature rather than linearly as explicitly defined by the problem's convolution model.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Wave Optics - Class 12 |
| Concept | Angular Resolution Limit |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |