In a double-slit experiment light of 480 nm and 600 nm illuminates the slits together. The bright fringes first coincide at:

4th order of 480 nm with 5th order of 600 nm

6th order of 480 nm with 5th order of 600 nm

3rd order of 480 nm with 2nd order of 600 nm

In a double-slit experiment light of 480 nm and 600 nm…

Answer: 5th order of 480 nm with 4th order of 600 nm.

A 5th order of 480 nm with 4th order of 600 nm
B 4th order of 480 nm with 5th order of 600 nm
C 6th order of 480 nm with 5th order of 600 nm
D 3rd order of 480 nm with 2nd order of 600 nm

Correct answer: A. 5th order of 480 nm with 4th order of 600 nm

Explanation: Coincidence needs n₁λ₁ = n₂λ₂: 480 n₁ = 600 n₂ gives n₁:n₂ = 5:4, so the 5th order of 480 nm meets the 4th of 600 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.

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In a double-slit experiment light of 480 nm and 600 nm illuminates the slits together. The bright fringes first coincide at:

Concept context

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