
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
In the Cartesian coordinate system $xOy$, the parametric equation of the straight line $l$ is $\begin{cases} x=- \dfrac {1}{2}t \\ y=3 \sqrt {3}+ \dfrac { \sqrt {3}}{2}t\end{cases}$ (where $t$ is a parameter). A polar coordinate system is established with the origin $O$ as the pole and the non-negative half-axis of $x$ as the polar axis. The polar equation of the circle $C$ is $\rho=2\cos \theta$. The ray $OM: \theta= \dfrac {\pi}{3} (\rho \geqslant 0)$ intersects the circle $C$ at points $O$ and $P$, and intersects the straight line $l$ at point $Q$.
   
(Ⅰ) Find the polar equation of the straight line $l$;  
(Ⅱ) Find the length of the line segment $PQ$.

Present the answer in LaTex format: \boxed{Your answer}
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