# Physics Question help

I have to calculate the voltage across a 50 uF (micro Farad) capacitor. The circuit voltage supply is 20V the capacitor is in series. There's an 100uF capacitor and 70uF capacitor parallel in the same circuit. I know that V=Charge/Capacitance however I don't know how to work out the charge to find the voltage. The capacitance of the circuit is 38.6uF
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Original post by ToonLegend_
I have to calculate the voltage across a 50 uF (micro Farad) capacitor. The circuit voltage supply is 20V the capacitor is in series. There's an 100uF capacitor and 70uF capacitor parallel in the same circuit. I know that V=Charge/Capacitance however I don't know how to work out the charge to find the voltage. The capacitance of the circuit is 38.6uF

Let C1 =50 μF, C2 = 100 μF and C3 = 70 μF.

Knowing that C2 and C3 are in parallel, so let's call the effective capacitance to be C23.

The p.d. across C1 and C23 is V1 and V23, respectively.
Since the power supply is in series with C1 and C23, we have
20 = V1 + V23 ---- Eqn(1)
Knowing that V = Q/C, rewrite eqn(1)

$\dfrac{Q_{\text{tot}}}{C_{\text{tot}}} = \dfrac{Q_1}{C_1} + \dfrac{Q_{23}}{C_{23}}$

Ctot = 38.6 μF
Do you know how are Qtot, Q1 and Q23 related?
Once you know their relationship, you can work out the p.d. across C1.