In the ideal double-slit experiment, when a glass-plate (refractive index 1.5) of thickness t is introduced in the path of one of the interfering beams (wave-length λ), the intensity at the position where the central maximum occurred previously remains unchanged. The minimum thickness of the glass-plate is
Answer & explanation
Correct answer: option 1
Path difference = $(μ - 1)t = nλ$;
For minimum t, n = 1;
$∴ t = 2λ$