Math Is Fun Forum

CIV

Member

Registered: 2014-11-09

Posts: 74

The Algebra involved with Ohms and Joules Law.

I'm a bit confused here. I'm pretty decent with my Algebra, but there's something that is confusing me here. I have these problems to do in my electronics class that is nothing more than something for values that involves Ohm and Joules law. I'm given just enough info to solve for some value, but I must comprise a formula to do it, using what I know about these two laws. Im a bit confused with the algebra involved with assembling these formulas.

An example problem...

I have to solve for I, knowing that that:

The Laws:
V=IR
P=VI

This is what I did:

Now I come to this point...

... and naturally want to do this:

But this solves for voltage not current. After messing around with it some I learned that it's:

This confuses me:( What's the deal here? There was another scenario where I did the same thing and the result was wrong.

Is it because this:

and this are not the same?

Because I would technically be replacing the V with a 1? Is that wrong? Well, I mean it's wrong because it obviously doesn't work. I remember from Algebra 2 with complex fractions that a 1 was added in there somewhere and then the fraction were reciprocated and then multiplied.

zetafunc

Moderator

Registered: 2014-05-21

Posts: 2,432

Website

Re: The Algebra involved with Ohms and Joules Law.

Now I come to this point...

... and naturally want to do this:

That isn't right. What you mean to do is this:

.

You can now substitute for P and R, to solve for I.

CIV

Member

Registered: 2014-11-09

Posts: 74

Re: The Algebra involved with Ohms and Joules Law.

You multiply both sides by I, oh OK. Before reading this I came to this:

... and you get where I'm going with that. Your way look more correct than mine though, because your way makes more sense than mine. Thanks.