How Do You Calculate Interference Fringes in a Double Slit Experiment?

[roam]

Homework Statement

A laser beam ( λ = 694 nm) is incident on two slits 0.100 mm apart. Approximately how far apart (in m) will the bright interference fringes be on the screen 5.00 m from the double slits?

Homework Equations

[tex]y=L\left( \frac{m \lambda}{d} \right)[/tex]

The Attempt at a Solution

[tex]y_{m+1}-y_m = L \left(\frac{(m+1)\lambda}{d} \right) - L \left( \frac{m \lambda}{d}\right)[/tex]

[tex]= L\frac{\lambda}{d}= 5 \left( \frac{694}{1 \times 10^{-4} m} \right)[/tex]

=34700000

So I got the distance between adjacent fringes to be 34700000 which is a very huge number. But the right answer must be 3.47 × 10^–2. Any help is appreciated.

 

[Doc Al]

For one thing, the wavelength is 694 nm, not 694 m. (nm = nanometer)