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In Young’s double-slit experiment, blue light of wavelength 4360 Å and green light of wavelength 5460 Å are used separately. If x denotes the distance of the fourth bright fringe from the central bright fringe, then which statement is correct?

1. x for blue light is equal to x for green light
2. x for blue light is greater than x for green light
3. x for blue light is less than x for green light
4. x(blue) / x(green) = 5460 / 4360

Correct answer: x for blue light is less than x for green light

Solution

Fringe position x = n*lambda*D/d is proportional to wavelength. Green (5460 A) exceeds blue (4360 A), so x for blue light is less than x for green light.

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