# 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 Senior Member

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
214
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 Senior Member

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 Senior Member

May 26, 2009
1,146
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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
20
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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