The product of (voltage) times (current, in Amperes) is POWER.
Answer:
The new voltage between the parallel plates of the capacitor is 18V, because for a constant electric field, doubling the space between the parallel capacitor plates, will also double the potential difference (voltage) between the plates.
Explanation:
ΔV = E*Δd
Where;
ΔV is the change in potential difference
Δd is the change in the distance between the parallel plates
E is the electric field potential.
Assuming a constant electric field; 
when the spacing between the capacitor plates is doubled, d₂ = 2d₁
v₂ = (v₁*d₂)/(d₁)
v₂ = (v₁*2d₁)/(d₁)
v₂ = 2v₁
v₂ = 2(9) = 18 V
Therefore, for a constant electric field, doubling the space between the parallel capacitor plates, will also double the potential difference (voltage).
Longer the air column is the more harmonics are created. due to the longer column the waves have more space to bounce off of the sides of the column to create more harmonics.