# What is the number of bright fringes appearing between the two minima of the diffraction pattern?

A double-slit system with individual slit widths of 0.0250 mm and a slit separation of 0.150 mm is illuminated with 480 nm light directed perpendicular to the plane of the slits. What is the number of complete bright fringes appearing between the two first order minima of the diffraction pattern?
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Given:
Individual slit width:

Slit separation:

Wavelength of light:

In the double slit experiment, there will be interference due to difference in the phase of two paths and diffraction (bending of light) in the single slit.
Now, the first minima will be given as:
$a\mathrm{sin}\theta =\lambda$
Now, the angular locations due to interference is:
From equation,
${m}_{2}=\frac{d}{a}$
Substituting the known values and solving,
${m}_{2}=\frac{0.15}{0.025}\phantom{\rule{0ex}{0ex}}{m}_{2}=6$
Therefore, there are 5 complete bright fringes in each side along with the central maximum. Hence, the number of complete bright fringes appearing between the two, first order minima of the diffraction pattern is 11.