In YDSE, wavelengths 600 nm and 480 nm are used simultaneously. The minimum order of the bright fringe of 480 nm that coincides with a bright fringe of 600 nm is:
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In YDSE, wavelengths 600 nm and 480 nm are used simultaneously. The minimum order of the bright fringe of 480 nm that coincides with a bright fringe of 600 nm is:

G1 Physics · Accepted Answer

Coincidence requires n₄₈₀(480)=n₆₀₀(600). Thus 4n₄₈₀=5n₆₀₀. Smallest integers are n₄₈₀=5 and n₆₀₀=4. Hence the 5th bright fringe of 480 nm coincides.