Answer: plane wavefront.
- A plane wavefront
- B spherical wavefront
- C cylindrical wavefront
- D converging wavefront
Correct answer: A. plane wavefront
Explanation: Rays from a source at the focus emerge parallel after the lens, so the emerging wavefront is plane.
Two coherent slits S₁ and S₂ act as secondary sources; at each point on the screen, the path difference between light from S₁ and S₂ determines whether the waves arrive in phase (bright fringe) or out of phase (dark fringe), producing the characteristic alternating fringe pattern.
Concept context
Huygens principle, Young's double slit, diffraction, polarization. Essential for JEE.