Find an Expression For the Voltage

AI Thread Summary
The discussion revolves around finding an expression for voltage in a capacitor circuit. The original poster calculated the equivalent capacitance and derived the voltage across one capacitor, but sought confirmation on their approach. Other participants clarified that the voltage across the capacitors can also be derived using voltage division principles and complex impedance. They emphasized that the original formula for charge (Q = CV) is correct and provided alternative methods to arrive at the same voltage expression. Overall, the calculations were validated, and additional methods were suggested for clarity.
mmmboh
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Hey, so I have an assignment and this is one of the questions on it, I did it but I am not sure if what I did is right.
2chpe38.jpg


What I did was find Ceq=(C1C2)/(C1+C2))

So then Q=CV(t)=(C1C2)/(C1+C2))V(t)

Then I found the voltage across C2=Q/C2=(C1C2)/(C1+C2))V(t)/C2=(C1)/(C1+C2))V(t)

And then V0=V(t)-(C1)/(C1+C2))V(t)

Can anyone tell me if what I did is right or if I am completely off?
 
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mmmboh said:
Hey, so I have an assignment and this is one of the questions on it, I did it but I am not sure if what I did is right.
2chpe38.jpg


What I did was find Ceq=(C1C2)/(C1+C2))

So then Q=CV(t)=(C1C2)/(C1+C2))V(t)
For starters, shouldn't it be Q = CVT = (C1C2VT)/(C1+C2)?
 
mmmboh said:
Hey, so I have an assignment and this is one of the questions on it, I did it but I am not sure if what I did is right.
2chpe38.jpg


What I did was find Ceq=(C1C2)/(C1+C2))

So then Q=CV(t)=(C1C2)/(C1+C2))V(t)

Then I found the voltage across C2=Q/C2=(C1C2)/(C1+C2))V(t)/C2=(C1)/(C1+C2))V(t)

And then V0=V(t)-(C1)/(C1+C2))V(t)

Can anyone tell me if what I did is right or if I am completely off?
You could have just found the voltage across c_1 like you did for c_2 and stopped there.: \frac{q}{c_1}=v_o=v(t) \frac{c_2}{c_1+c_2}
Your expression you found simplifies to that anyway:
v_o=v(t)[1 - \frac{c_1}{c_1+c_2}]
v(t)[\frac{c_1+c_2}{c_1+c_2} - \frac{c_1}{c_1+c_2}]= v(t) \frac{c_1+c_2 - c_1}{c_1+c_2}=v(t) \frac{c_2}{c_1+c_2}
I don't know if you know about complex impedance yet but you can also use that to arrive to the same answer:
Z_T = Z_C_1 + Z_C_2
Z_T = \frac{1}{\omega c_1}+\frac{1}{\omega c_2}
These impedances work like resistance with v = IR. Therefore,voltage division works too.
v_o = v(t) \frac{ Z_C_1}{Z_T}
v_o = v(t) \frac{ \frac{1}{\omega c_1}}{\frac{1}{\omega c_1}+\frac{1}{\omega c_2}}
Omegas cancel and you come to the same answer.
 
Last edited:
Leptos said:
For starters, shouldn't it be Q = CVT = (C1C2VT)/(C1+C2)?
Just for the record: no, Q=CV for a capacitor, as the OP said.
 
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