A parallel plate capacitor of capacitance $C$ is as shown. A thin metal plate A is placed between the plates of the given capacitor in such a way that its edges touch the two plates as shown. Find the capacitance across $P$ and $Q$.
I think the answer is $0$ as the current literally passes through the capacitor since metal is touching both the plates.
But the answer given is infinity, "because $d$ becomes zero". What does this mean? Why is my answer wrong?