# Conductor replaced by an inductor.

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#### alphacat

##### New Member
Hey,

I'm trying to figure out two things.

1. Why a single conductor is considered as an inductor?

2. Why two parallel plates form an inductor which its inductance depends on the distance between them?

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#### Chippie

##### Member
when a current passes through it generates a magnetic field...when a further conductor is placed parallel to it a voltage is generated....Michael Faraday....the father of transformers...

The magnitude of the currents is determined by the proximity...
how welding transformers work........

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#### crutschow

##### Well-Known Member
All wires have inductance (see Inductance of a Straight Wire: A Calculator). It's small but has an effect at higher frequencies.

Parallel plates form a capacitor, not an inductor (perhaps that's what you meant?).

Capacitance is caused by the electric field between two conductors attracting charges from the opposite side. The larger and closer together the plates are, the more charge that's attracted for a given voltage, giving a larger capacitance.

#### alphacat

##### New Member
Thanks guys,

Regarding the parallel plates, I did mean that parallel plates form an inductor, I read it in the book and summarize it in the following picture: This is the book by the way, if its interesting you (chapter 10):
http://www.ece.rutgers.edu/~orfanidi/ewa/

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#### crutschow

##### Well-Known Member
The inductance goes down as the plates become closer together because the magnetic field, caused by the current in the top conductor, is better canceled by the magnetic field from the current (going in the opposite direction) in the bottom conductor. It's the changing magnetic field around a conductor carrying an AC current that causes the inductance. The more this field is canceled, the lower the inductance.

#### Tesla23

##### Member
The inductance goes down as the plates become closer together because the magnetic field, caused by the current in the top conductor, is better canceled by the magnetic field from the current (going in the opposite direction) in the bottom conductor. It's the changing magnetic field around a conductor carrying an AC current that causes the inductance. The more this field is canceled, the lower the inductance.
Actually the field from the top conductor adds to the one from the bottom in the area between the conductors. The reason the inductance decreases when the gap reduces is that the area reduces, hence the flux linkage reduces.

alphacat, you need to understand a simple inductor first, for example a single loop of wire. For low frequencies, the shorted transmission line is like a long skinny loop, and as you increase the area of the loop you increase the inductance.

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#### alphacat

##### New Member
Thanks fellows.

As you said, its like a Cylindrical coil, which its inductance equals to µ*N²*A/L, and in our case, the width of the plates is the lenght of the coil, and the plates are like one big turn (N=1).

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#### alphacat

##### New Member
All wires have inductance (see Inductance of a Straight Wire: A Calculator). It's small but has an effect at higher frequencies.
It is said there that a straight wire has an inductance, but as far as i know, magnetic field is not enough to create inductance, but a magnetic flux thourgh a closed area is.

Meaning, there has to be a closed area where the magnetic field goes through.

So how come a straight line could have an inductance, unless it somehow forms a closed area?

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#### MrAl

##### Well-Known Member
Hi,

A moving electron can produce a magnetic field, the magnetic field can
oppose the movement of the electron, hence even space has inductance,
you dont even need a wire.

#### crutschow

##### Well-Known Member 