Find an Expression For the Voltage

In summary, the conversation is about finding the voltage across different capacitors in a circuit, and the OP has correctly calculated it using the formula Q=CV and voltage division.
  • #1
mmmboh
407
0
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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  • #2
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)?
 
  • #3
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 [tex]c_1[/tex] like you did for [tex]c_2[/tex] and stopped there.: [tex]\frac{q}{c_1}=v_o=v(t) \frac{c_2}{c_1+c_2}[/tex]
Your expression you found simplifies to that anyway:
[tex]v_o=v(t)[1 - \frac{c_1}{c_1+c_2}][/tex]
[tex]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}[/tex]
I don't know if you know about complex impedance yet but you can also use that to arrive to the same answer:
[tex]Z_T = Z_C_1 + Z_C_2[/tex]
[tex]Z_T = \frac{1}{\omega c_1}+\frac{1}{\omega c_2}[/tex]
These impedances work like resistance with v = IR. Therefore,voltage division works too.
[tex]v_o = v(t) \frac{ Z_C_1}{Z_T}[/tex]
[tex]v_o = v(t) \frac{ \frac{1}{\omega c_1}}{\frac{1}{\omega c_1}+\frac{1}{\omega c_2}}[/tex]
Omegas cancel and you come to the same answer.
 
Last edited:
  • #4
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.
 

1. What is an expression for voltage?

An expression for voltage is a mathematical representation of the potential difference between two points in an electrical circuit. It is usually denoted by the symbol V and measured in volts (V).

2. How is voltage calculated?

Voltage is calculated by dividing the amount of energy transferred (measured in joules) by the electric charge (measured in coulombs). This can be represented by the formula V = E/Q, where V is voltage, E is energy, and Q is charge.

3. What is the unit of measurement for voltage?

The unit of measurement for voltage is the volt (V). Other common units for voltage include millivolts (mV) and kilovolts (kV).

4. What factors can affect the voltage in a circuit?

The voltage in a circuit can be affected by factors such as the type of power source, the resistance of the circuit components, and the presence of other electrical devices connected to the circuit.

5. How does voltage relate to current and resistance?

According to Ohm's law, voltage (V) is directly proportional to current (I) and resistance (R). This means that an increase in voltage will result in an increase in current, while an increase in resistance will result in a decrease in current.

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