My Math Forum  

Go Back   My Math Forum > College Math Forum > Differential Equations

Differential Equations Ordinary and Partial Differential Equations Math Forum

LinkBack Thread Tools Display Modes
March 16th, 2011, 08:07 AM   #11
Senior Member
Joined: Feb 2011

Posts: 150
Thanks: 0

Re: Differential equations

ahh for god sake. cheers

Last question today its another Electronics orientated problem, which i hate. but ive attempted

In a LR circuit with applied voltage E=10(1-e^-0.1t) the current i is given by L di/dt + Ri =10(1-e^0.1t).

If the initial current is i0m derive the result :

i=10/R - (100/10R-L) e^-0.1t + [ i0 + 10L/R(10R-L) ] e^-Rt/L.

My working.

L di/dt + Ri = 10 (1-e^-0.1t)

di/dt + (R/L)i = 10(1-e^-0.1t) / L

?(x)=e^?R/L dt = e^Rt/L Multiply by integrating factor

e^Rt/L di/dt + R/L e^Rt/L i = 10(1-e^-0.1t)/L e^Rt/L

d/dt (e^Rt/L i) = 10(1-e^-0.1t)/L e^Rt/L

?d/dt (e^Rt/L i) dt =?10(1-e^-0.1t)/L e^Rt/L dt

e^Rt/L i = ?10-10e^-0.1t/L e^Rt/L dt

e^Rt/L i = 10t +100e^-0.1t + L/R

thats as far as i got as i was digging a deep whole i feared
jakeward123 is offline  
March 16th, 2011, 08:45 AM   #12
Senior Member
MarkFL's Avatar
Joined: Jul 2010
From: St. Augustine, FL., U.S.A.'s oldest city

Posts: 12,211
Thanks: 521

Math Focus: Calculus/ODEs
Re: Differential equations

You did well until you integrated the right side of the equation. You did not distribute the integrating factor.

You have the IVP:


Put the linear ODE into standard form:

Calculate integrating factor

Now use initial conditions to determine C:

Thus the solution satisfying initial conditions is:

MarkFL is offline  

  My Math Forum > College Math Forum > Differential Equations

differential, equations

Search tags for this page
Click on a term to search for related topics.
Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
Partial Differential Differential Equations rishav.roy10 Differential Equations 0 August 21st, 2013 05:59 AM
Need help differential equations? Antuanne Differential Equations 2 June 6th, 2013 08:10 AM
Differential Equations giga.chalauri Differential Equations 2 April 3rd, 2013 10:34 AM
differential equations thebigbeast Differential Equations 2 September 11th, 2012 09:27 AM
Three differential equations _TJ_ Differential Equations 1 August 29th, 2009 06:08 PM

Copyright © 2019 My Math Forum. All rights reserved.