Answer: 1000 nm.
- A 1000 nm
- B 500 nm
- C 200 nm
- D 100 nm
Correct answer: A. 1000 nm
Explanation: Each fringe corresponds to mirror movement of λ/2 (path difference changes by λ for each fringe). λ = 2 × mirror movement / fringe count = 2 × 0.1mm / 200 = 0.001 mm = 1000 nm.
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.