# Solving parallel RL circuit

**URL:** <https://community.freefem.org/t/solving-parallel-rl-circuit/1977>\
**Category:** General Discussion\
**Created:** [August 31, 2022, 8:49am UTC](https://community.freefem.org/t/solving-parallel-rl-circuit/1977 "2022-08-31T08:49:58Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![gael](https://avatars.discourse-cdn.com/v4/letter/g/a698b9/32.png) [@gael](https://community.freefem.org/u/gael)\
**Post date:** [August 31, 2022, 8:49am UTC](https://community.freefem.org/t/solving-parallel-rl-circuit/1977/1 "2022-08-31T08:49:58Z")

</div>

Hi! I am a material science major so my question about electricity may be trivial:  
I am trying to get a graph voltage Vs current with a current loading according to a function of time.  
let’s say Iop = t\*1 t in sec until 50 A.

 ![image](https://canada1.discourse-cdn.com/flex030/uploads/freefem/original/2X/b/be44da7b51bfeaf1f7d143a8c9354d1a5481c27b.png)

From what I know of electricity, here I cannot use complex numbers so I get this:

Iop(t) = Ir(t) + Il(t)

Iop(t) = \frac{V(t)}{R} + \int\_t\frac{V(t)}{L}dt

or another thing I could use:

Iop(t) = \frac{L}{R}\frac{dIl(t)}{dt} + Il(t)

Il being the current going through the inductor and Ir the current going through the resistor.

From there I am a bit lost:  
I thought about using part of the code taken from there [FreeFem++ users | Main \>\> ExampleBySilvainAuliac](https://www.um.es/freefem/ff++/pmwiki.php?n=Main.ExampleBySilvainAuliac) :

```auto
int np=100;
mesh Th = square(np,1,[x,y/50]); //transformation for viewing comfort
plot(Th,wait=1,aspectratio=1);
fespace Vh(Th,P1);
Vh u,v;
func f=1.;
solve Laplace1D(u,v) = int2d(Th)(dx(u)*dx(v)) - int2d(Th)(v*f) + on(2,4,u=0.);
plot(u,wait=1,dim=3,fill=1);

```

To have a 1D time axis and calculate the Iop and V on it.

Would this work? if yes how should I solve the problem and if not how should I proceed?

---

<div class="post-metadata">

**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [September 20, 2022, 4:03pm UTC](https://community.freefem.org/t/solving-parallel-rl-circuit/1977/2 "2022-09-20T16:03:54Z")

</div>

FreeFEM is no a good tools to solve you problem!

---

<div class="post-metadata">

**Author:** ![asadmath18](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/asadmath18/32/3744_2.png) [@asadmath18](https://community.freefem.org/u/asadmath18)\
**Post date:** [June 7, 2026, 8:15am UTC](https://community.freefem.org/t/solving-parallel-rl-circuit/1977/3 "2026-06-07T08:15:01Z")

</div>

Hi, have you solved this circuit problem? I am going to code FSEI problem with similar circuit. If it is feasible, i will try. Thank you