In a single slit diffraction pattern, a light of wavelength 6000 $\mathop A\limits^o$ is used. The distance between the first and third minima in the diffraction pattern is found to be $3 \mathrm{~mm}$ when the screen in placed $50 \mathrm{~cm}$ away from slits. The width of the slit is $\underline{\hspace{2cm}}$$\times 10^{-4} \mathrm{~m}$.