Answer: coherent, with a constant phase difference.
- A coherent, with a constant phase difference
- B of different frequencies
- C of equal amplitude only
- D of random phase
Correct answer: A. coherent, with a constant phase difference
Explanation: Sustained interference requires coherent sources maintaining a constant phase difference.
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.