In a Young’s double slit experiment, slits
are separated by $0.5\; mm$, and the screen
is placed $150\; cm$ away. A beam of light
consisting of two wavelengths, $650 \;nm$ and $520\; nm$, is used to obtain interference
fringes on the screen. The least distance from the common central maximum to the
point where the bright fringes due to both the wavelengths coincide is :
