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Kernul
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Homework Statement
Three capacitors ##C_a = C, C_b = 2C, C_c = 3C## are positioned like in the figure. The A capacitor's electrode has a ##V_a = 20 V##, while the B capacitor's electrode has a ##V_b = 80 V##. What is the electric potential ##V_3## of the C capacitor's electrode?
Homework Equations
##Q = C \Delta V##
The Attempt at a Solution
So, since ##Q = C \Delta V = C (V_1 - V_2)## we can write the electric charge for all three the capacitors.
##Q_a = C_a (V_a - V_c) = C (20 - V_c)##
##Q_b = C_b (V_b - V_c) = 2C (80 - V_c)##
##Q_c = C_c (V_c - 0) = 3C V_c##
Knowing from the picture that A and B are parallel we have a total electric charge as:
##Q = Q_a + Q_b = C (20 - V_c) + 2C (80 - V_c) = C (180 - 2V_c)##
What we end up with is a series so the total electric charge doesn't change. This means that:
##Q = Q_c##
so
##C (180 - 2V_c) = 3C V_c##
##V_c = 36 V##
Is this correct? Or did I mess up something/my method wasn't correct?