In Young's double-slit experiment, the distance between slits and...

When the angular fringe width in the interference pattern becomes less than the angular resolving power of the person's eye, the fringes will disappear.

The angular fringe width ${\theta}_{0} = \dfrac{\beta}{D} = \dfrac{\lambda}{{d}_{0}}$

${d}_{0} = \dfrac{\lambda}{{\theta}_{0}} = \dfrac{600 \times {10}^{- 9}}{( \dfrac{1}{60} \times \dfrac{\pi}{180} )}$

${d}_{0} = \dfrac{600 \times 60 \times 180 \times {10}^{- 9}}{\pi}m = 2\text{mm}$