Solving circuit using Laplace Transforms

Click For Summary
The discussion revolves around solving a circuit to find the voltage across an inductor using both differential equations and Laplace transforms. The user initially obtained a solution for the current in the inductor using Mathematica but struggled to replicate this result with Laplace transforms. A key insight was provided regarding the voltage drop across the inductor, which helped the user correct their approach and achieve the correct answer. The user expressed intent to further solve the circuit by hand using differential equations and plans to seek additional help if needed. The conversation highlights the importance of careful attention to circuit equations in obtaining accurate results.
perplexabot
Gold Member
Messages
328
Reaction score
5
Hi all. I need to find the voltage across the inductor. I begin by solving for the current in the inductor. I first solved a circuit using differential equations (with mathematica) and achieved an answer for current in inductor of: iL(t) = E^(-5 t) (-0.75 + 1.25 E^(4 t)

Later, I tried to solve the same circuit using Laplace transforms and was not able to yield the same answer (or anything close). The original circuit and my approach for solving the circuit using Laplace transforms is attached as a pdf file. In the pdf file, I am attempting to solve for the current in the inductor. I get an equation for iL(s), however, when I take the inverse laplace, the answer looks nothing like my diff-eq iL(t). Please let me know where I am going wrong. Hints are preferred over answers. Thank you.
 

Attachments

Engineering news on Phys.org
In your loop 2 equation the voltage drop across inductor should be (i2)sL.
 
the_emi_guy said:
In your loop 2 equation the voltage drop across inductor should be (i2)sL.

WOW, you are so right. I can't believe I didn't see that. Thank you so much. I will give it another go. Hopefully I will not run into another error. Thanks again.
 
Thanks the_emi_guy. That simple fix gave me the exact answer.
 
You're welcome
 
I am now trying to solve the circuit by hand using differential equations. I have attempted it twice and went over it many times but have not achieved the correct answer (i am close though). I may upload my attempt tonight and hopefully you (or someone else) may help me with that too.
 
I am trying to understand how transferring electric from the powerplant to my house is more effective using high voltage. The suggested explanation that the current is equal to the power supply divided by the voltage, and hence higher voltage leads to lower current and as a result to a lower power loss on the conductives is very confusing me. I know that the current is determined by the voltage and the resistance, and not by a power capability - which defines a limit to the allowable...

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 31 ·
2
Replies
31
Views
11K
Replies
13
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
5
Views
1K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 6 ·
Replies
6
Views
11K
  • · Replies 12 ·
Replies
12
Views
3K