# Double Slit Wave Interference - what is m?

Hi,
I'm doing a very simple problem, but I don't understand the diagram provided (see image below). What is m here?
I know that m is the order with respect to the central bright fringe, but there isn't a central bright fringe (assuming those circles are the bright fringes)?

## Homework Statement

Suppose the interference pattern shown in the figure is produced by monochromatic light passing through two slits, with a separation of 161 μm, and onto a screen 1.32 m away. What is the wavelength of light?

## Homework Equations

dsinθ = mλ (m = 0,1,2,3...) for constructive interference
dsinθ = (m + ½)λ (m = 0,1,2,3...) for destructive interference
tanθ = y/L

## The Attempt at a Solution

tanθ = (23mm)/(1.32m)
θ = 0.998°
λ = (dsinθ)/m = [(161μm)(sin(0.998))]/m

Thanks!

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gneill
Mentor
Hi snowcrystal42,

Welcome to Physics Forums!

From the diagram, what can you say about the separation between the individual maxima (or minima)? Can you concoct an expression for the distance between two successive maxima (or minima)?