Calculating Wavelength from Double-Slit Interference Pattern

[cupcakequeen]

Homework Statement

A double-slit interference pattern is created by two narrow slits spaced 0.21mm apart. The distance between the first and the fifth minimum on a screen 60cm behind the slits is 6.2mm. What is the wavelength of the light used in this experiment?

Homework Equations

gamma = d/L * Delta y

The Attempt at a Solution

delta y = 6.2mm/5 = 1.24*10 ^-3m
gamma = d/L delta y
= (2.1*10^-4m)/0.6m * 1.24*10^-3
= 434nm
but this is incorrect. Where did I go wrong?

 

[vela]

If the 6.2 mm was the distance between the first and second minima, would you say the distance between the minima is Δy = 6.2 mm/2?