PYQ LensCBSE Class 12 Physics PYQs
Physics papers reward clear reasoning as much as correct formulas. Work through real CBSE questions from electrostatics to semiconductors, and see the reasoning behind each mark.
- 20Papers
- 5Years
- 670Questions
Chapters with the most questions
| Chapter | Questions |
|---|---|
| Semiconductor Electronics | 71 |
| Current Electricity | 68 |
| Ray Optics and Optical Instruments | 66 |
| Moving Charges and Magnetism | 65 |
| Dual Nature of Radiation and Matter | 58 |
| Wave Optics | 47 |
| Atoms | 46 |
| Electromagnetic Induction | 45 |
Counted across the 20 papers listed on this page.
Try a sample question
From the CBSE Class 12 Physics Sample Paper 2027.
If wave front from star in nearby galaxy is detected by a telescope at the top of some mountain in India then the shape of the wavefront detected will be
- diverging spherical
- converging spherical
- plane
- cylindrical
Answer
C. plane
Explanation
A small distant star acts approximately as a point source. Its emitted wavefronts spread out as spheres. A wavefront is a surface on which the wave has the same phase.
The telescope receives only a tiny part of a sphere whose radius is enormous compared with the telescope's size. A small patch of a very large sphere looks almost flat, just as a small patch of Earth's curved surface can look flat nearby.
Far from the source, the incoming rays across the telescope's aperture are nearly parallel. A plane perpendicular to these parallel rays is an approximately plane wavefront.
This does not mean the star suddenly stops emitting spreading waves. It is a local approximation at the detector, made possible by the very large source distance. The mountain's location does not turn a remote star into a nearby source.
Final answer: C, plane.
A describes the full diverging spherical wavefront near a point source but misses the local far-distance approximation asked here. B describes convergence towards a focus, not the wavefront arriving before the telescope focuses it. D would suit a cylindrical source arrangement, not the stated remote point-like star. Keep 'approximately plane at the telescope' in the explanation.