In a double-slit experiment, light from two monochromatic light sources passes through the same double slit. The light from the first light source has a wavelength of 646 nm. Two different interference patterns are observed. If the 9th order bright fringe from the first light source coincides with the 11th order bright fringe from the second light source, what is the wavelength of the light coming from the second monochromatic light source?

Question

Anton Gaines

Physics

4 September, 14:44

In a double-slit experiment, light from two monochromatic light sources passes through the same double slit. The light from the first light source has a wavelength of 646 nm. Two different interference patterns are observed. If the 9th order bright fringe from the first light source coincides with the 11th order bright fringe from the second light source, what is the wavelength of the light coming from the second monochromatic light source?

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Glenn Knapp · Answer 1

Let λ be the required wavelength.

Two fringe patterns will be formed on the screen which will overlap each other. Let 9 th bright fringe of first coincides with 11 th bright fringe of second.

position of 9 the bright fringe of first = 9x 646 x D/d nm

position of 11 th bright fringe of second pattern = 11 x λ x D/d

now, 9 x 646 = 11 x λ

λ = 9 x 646 / 11 = 528.54 nm.