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bharat56
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Join Date: Jan 2011
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Basic Understanding of Electromagnetism

01/17/2011 10:17 AM

If I have a long insulated copper wire between a + and - terminal, there will be short as there is no resistance. However, if I wind the wire over a ferrous metal, there is no short. How does winding the same copper wire over a metal create a load? Is load also synonymous to resistance?
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TonyS
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#1

Re: Basic Understanding of Electromagnetism

01/17/2011 10:36 AM

You would be right with an AC supply where the reactance of the ferrous core restricts the current. With DC you have to rely on the resistance of the wire to limit the current.

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kvsridhar
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#2

Re: Basic Understanding of Electromagnetism

01/17/2011 10:40 AM

If I have a long insulated copper wire between a + and - terminal, there will be short as there is no resistance.

Not quite.Any length of wire will have resistance R = ρ*L/A.

However, if I wind the wire over a ferrous metal, there is no short.

If wound around a ferrous (or any) core, it will have Inductance in addition, a more complex formula that we will ignore for now. A ferrous core will give a far higher inductance to the coil than a core of non-magnetic material (or air). So the coil may or may not be a "short"

The inductance will become a "Reactance" only if the supply is AC. Not if it is DC as you say. In such an event, the current will rise exponentially with time, according to the formula I = Im*(1-e^-Rt/L). And I will be equal to E/R. No help from the inductance.

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#3
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Re: Basic Understanding of Electromagnetism

01/17/2011 11:14 AM

Thanks.
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electricalexpert65
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#4
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Re: Basic Understanding of Electromagnetism

01/18/2011 12:18 PM

Excellent KVS Sir! GA to you!
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kvsridhar
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#5
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Re: Basic Understanding of Electromagnetism

01/18/2011 9:48 PM

Hello, and thanks. You seem to be busy and aren't coming on CR4 often....we miss you

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electricalexpert65
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#6
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Re: Basic Understanding of Electromagnetism

01/19/2011 12:13 AM

Ya! I was on tour frm 25th December till 17th January. I don't have access to net while I am on tour. Only when I am back in my HQ I have access to net and hence the moment I am back at my HQ, I devour the CR4 contents. I too miss all of you during such periods of my absence.
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