Two lasers are shining on a double slit, with slit separation d. laser 1 has a wavelength of d/20, whereas laser 2 has a wavelength of d/15. the lasers produce separate interference patterns on a screen a distance 5.00 m away from the slits. part a which laser has its first maximum closer to the central maximum?

We know that separation between bright spots in a double slit experiment is:

Smaller the spacing is smaller the distance from the central maximum will be.
From the formula, we can see that spacing is proportional to the wavelength. 
Therefore bigger wavelength would give you bigger separation.
Knowing all this we can conclude that laser 1 will have its first maximum closer to the central maximum because its wavelength is smaller.

The correct answer is c

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