# Inductors

Discussion in 'Homework Help' started by alexander7, Oct 11, 2009.

1. ### alexander7 Thread Starter New Member

Oct 11, 2009
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How much potential energy is stored in a 5 μ H inductor that has a current of 2 ma flowing through it?

2. ### ELECTRONERD AAC Fanatic!

May 26, 2009
1,146
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Potential energy? I'm not accustomed to that term, I suppose you mean reactance? Then according to the equation:

$XL = 2 \pi f L$

Where:
• $f$ = Frequency
• $\pi$ = Pi, or approximately 3.14
• $L$ = Inductor value.
So, we can't really determine the reactance unless we know the frequency.

Last edited: Oct 11, 2009
3. ### ATM Member

Oct 8, 2009
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Use the equation, Energy = 0.5*L*I^2

0.5*(5X10^-6)*((2x10^-3)^2)

4. ### hgmjr Moderator

Jan 28, 2005
9,030
218
To put ATM's equation into math symbol notation:

$E_{\tiny L} =\frac{LI^2}{2}$

The corresponding equation for capacitors is:

$E_{\tiny C}=\frac{CV^2}{2}$

hgmjr

5. ### mik3 Senior Member

Feb 4, 2008
4,846
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E=0.5*L*I^2

Be careful of the units.

6. ### notxjack New Member

Sep 7, 2009
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potential energy is an unfancy word for voltage

7. ### ELECTRONERD AAC Fanatic!

May 26, 2009
1,146
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Of course! Now that I think of it, I remember...

8. ### Thav Member

Oct 13, 2009
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I don't think this is quite right. Energy is always referring to Joules (J), whereas voltage (or electric potential) is Joules per Coulomb J/C. This has always been a hazy subject for me, but what I think is that if you take an electron (1.6...E-19 Coulombs) and find its potential energy at one point in an electric field with respect to another point and then divide by the charge (that 1.6E-19) you get the voltage. So like the units hint we're talking about a potential energy per charge.

I'm being a little pedantic, but I feel voltage is such a difficult concept it's important to get the terminology straight to not obscure the physical basis.

9. ### ELECTRONERD AAC Fanatic!

May 26, 2009
1,146
16
In any case, potential energy is still denoted as "voltage", used by many. Even teachers use the termination in universities, and I've heard it a lot in the "self teaching" electronic guides.

People can think of the relationship between voltage, current, and resistance as the following:

Imagine a water pipe. More pressure will result in a higher potential of energy coming out; better known as voltage. The higher the pressure, the higher the potential. If we widen the pipe, we get more current. However, if we put a resistor in the pipe, it would lessen the current. That's how I've always found the relationships for ohms law.

10. ### Ratch New Member

Mar 20, 2007
1,068
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notxjack,

Not true. See the first post of the link below.

Thav,

Good for you. You are a "right thinker".

ELECTRONERD,

Why not "imagine" it the way it really is? As explained in the first post of the link below.

Ratch

11. ### notxjack New Member

Sep 7, 2009
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Yeah, my bad. Integrate work to get the 1/2 mv^2 dual for inductors, which I think is 1/2 LI^2