Answer: nλ (integer multiple of wavelength).
- A nλ (integer multiple of wavelength)
- B (2n-1)λ/2, the condition for destructive interference
- C nλ/2, half the integer-multiple condition
- D (2n+1)λ, an odd multiple offset from the true condition
Correct answer: A. nλ (integer multiple of wavelength)
Explanation: Constructive interference (bright fringes) occurs when path difference = nλ (0, λ, 2λ, ...). Destructive interference occurs at odd multiples of λ/2.
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.