Nodal analysis question -- circuit analysis

In summary, the conversation discusses using nodal analysis to find the current i in a circuit with given equations. The attempt at a solution involves writing node equations and solving for V, but the result does not match the expected answer. Possible mistakes include incorrect values for the left capacitor and the equation format used.
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Homework Statement


We have the circuit in the figure.I have to find the current i using nodal analysis
PPsWAsW.jpg


Homework Equations


1/6 F =-3j
1/2 F= -j
1/2 H= j

The Attempt at a Solution



So we have the equations
Node V1 : [(7-V1)/(4-3j) ]=[ V1/3 ]+ [(V1-V)/-j]
Node V : [(V1-V)/-j] =(V )+ (V/j)
In the V node we multiply by j each side so we have -(V1-V)=jV+V so -V1=jV
I place this in the first node so we have
In the first node we have [(7+jV)(4+3j)]/[(4-3j)(4+3j)] = -jV/3 + [(-jV-V)/-j]
We have 1.12 +0.84j-0.16jV-0.12V=-0.33JV+V-jV
Here I find V =0.1+0.85j
Now to find i I think I need to divide this by 1/2 H so by j
Problem is ,the result in my book is i=0.75 cos2t which I don't get here so where is my mistake?
 
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  • #2
Elaia06 said:

Homework Statement


We have the circuit in the figure.I have to find the current i using nodal analysis
PPsWAsW.jpg


Homework Equations


1/6 F =-3j
1/2 F= -j
1/2 H= j

The Attempt at a Solution



So we have the equations
Node V1 : [(7-V1)/(4-3j) ]=[ V1/3 ]+ [(V1-V)/-j]
Node V : [(V1-V)/-j] =(V )+ (V/j)
In the V node we multiply by j each side so we have -(V1-V)=jV+V so -V1=jV
I place this in the first node so we have
In the first node we have [(7+jV)(4+3j)]/[(4-3j)(4+3j)] = -jV/3 + [(-jV-V)/-j]
We have 1.12 +0.84j-0.16jV-0.12V=-0.33JV+V-jV
Here I find V =0.1+0.85j
Now to find i I think I need to divide this by 1/2 H so by j
Problem is ,the result in my book is i=0.75 cos2t which I don't get here so where is my mistake?

First, the value of the left capacitor looks to be 1/6 Farad, not 1/3 Farad, right? Does that change your first equation?

Second, I prefer to write the node equations as the sum of all currents leaving the node = 0. That way I don't have to worry about signs of currents.

Could you see if you want to change the first equation, and maybe re-write the equations in the form that I suggested? That will make it a lot easier to check your work. Thanks.
 

Related to Nodal analysis question -- circuit analysis

1. What is nodal analysis and how is it used in circuit analysis?

Nodal analysis is a method used in circuit analysis to determine the voltage and current at different points, or nodes, in a circuit. It involves creating equations based on Kirchhoff's Current Law and Ohm's Law to solve for the unknown variables.

2. How do you identify the nodes in a circuit for nodal analysis?

Nodes are points in a circuit where two or more components are connected. They are usually marked with a dot and can also be identified by looking for points where the wires intersect or branch out.

3. What is the difference between a supernode and a regular node in nodal analysis?

A supernode is a combination of two or more regular nodes in a circuit, formed when a voltage source is connected between two nodes. The voltage across a supernode is treated as an unknown variable in nodal analysis, while the voltage across a regular node is known.

4. What are the advantages of using nodal analysis in circuit analysis?

Nodal analysis allows for a systematic and efficient approach to solving circuits, as it reduces the number of equations needed to solve for the unknown variables. It also provides a better understanding of the circuit's behavior and can be applied to both linear and non-linear circuits.

5. Are there any limitations to using nodal analysis in circuit analysis?

Nodal analysis can become complex when dealing with circuits that have a large number of nodes or non-linear components. It also assumes that all components in the circuit are ideal, which may not always be the case in real-world circuits.

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