Answer: Red.
- A Red
- B Violet
- C Blue
- D Green
Correct answer: A. Red
Explanation: In the visible spectrum, red light has the longest wavelength (~700 nm) and violet has the shortest (~400 nm). VIBGYOR order from short to long wavelength.
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.