I know the answer is [MATH]12[/MATH].
My question is what if they asked, what is the charge on the capacitor [MATH]C_2[/MATH]?
This is my answer.
Since [MATH]Q_1[/MATH] and [MATH]Q_2[/MATH] (charges) are in series, the same current will flow in both capacitors (my assumption).
[MATH]Q_2 = V\left(\frac{1}{C_1} + \frac{1}{C_2} \right)^{-1} = 4\left(\frac{1}{2 \cdot 10^{-6}} + \frac{1}{4 \cdot 10^{-6}} \right)^{-1} = 5.3 \ \mu C[/MATH]
Is my answer correct? I have a doubt because [MATH]C_1[/MATH] and [MATH]C_2[/MATH] have different dielectric materials. Shouldn't they have different currents or charges (even if they are in series)? Or that violates the rules of electric circuits?