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 6.00 m away from the slits. Which laser has its first maximum closer to the central maximum?

The first laser

Explanation:

Using the equation

ym = m*λ*L/d

so for the first max for each one m =1

so for laser 1

y = (d/20)*(6.0m)/d

the d cancel out so we have

y = 6.0m /20 = 0.3

for laser 2 we do the same thing

y = 6.0m/15 = 0.4

y ( laser1 ) < y ( laser2 )

(1) hence first maxima of laser1 is closest to central maxima

Δy = 0.4m -0 .3 m = 0.1m