The ratio of intensities at two points $P$ and $Q$ on the screen in a Young's double slit experiment where phase difference between two waves of same amplitude are $\frac { \pi } { 3 }$ and $\frac { \pi } { 2 }$, respectively are\\
(1) $2 : 3$\\
(2) $1 : 3$\\
(3) $3 : 1$\\
(4) $3 : 2$