What Is an INDUCTOR??

[rag's]

Hi,
How does an INDUCTOR AND A STRAIGHT WIRE differ?how come the resistance offered by an inductor changes with frequency??

 

[Willbe]

Hi,
How does an INDUCTOR AND A STRAIGHT WIRE differ?how come the resistance offered by an inductor changes with frequency??

Even a short piece of straight wire has a few nanohenries of inductance.

The reactance changes with frequency and the skin effect changes the resistance with freq.

These are "properties" of inductance, just as mass is one property of material.

There are four undefinables: mass, length, time and charge, and since the "dimension" of inductance can be expressed as one or more of these, I guess it is also indefinable.

The "dimension" of "speed" is L/T or L(T^-1).
For inductance, it is
M(L^2)(Q^-2)
The Farad has all of them: M, L, T and Q.

 

[Googlyhead]

Inductor - Wikipedia, the free encyclopedia

See 'hydraulic model...' for a starting point.

It differs from a straight wire as one coil induces a current in the next (electric current causes magnetic field, which in turn causes electric current)

 

[rag's]

Thank you guys..I also found information related to this later.. i'd like to share it with u..The original extract was
When a current flows into an inductor, it doesn't go round and round and round the turns, taking its time to get to the other end. An inductor wound with 100 feet of wire behaves nothing like a 100 foot wire. Why? It's because when the current begins flowing, it creates a magnetic field. This field couples to, or links with, the other turns. The portion of the field from one turn that links with the others is the measurable quantity called the coefficient of coupling. For a good HF toroid, it's commonly 99% or better; solenoids are lower, and vary with aspect ratio. The field from the input turn creates a voltage all along the wire in the other turns which, in turn, produce an output current (presuming there's a load to sustain current flow). Consequently, the current at the input appears nearly instantaneously at the output. Those who are physics oriented can have lots of fun, I'm sure, debating just how long it takes. The field travels at near the speed of light, but the ability of the current to change rapidly is limited by other factors.

So please flush your minds of the image of current whirling around the coil, turn by turn, wending its way from one end to the other. It doesn't work at all like that. The coupling of fields from turn to turn or region to region is what brings about the property of inductance in the first place.
So from this it will also be easy to understand why the resistance of an inductor increases with frequency..

 

[john1]

https://www.w8ji.com/inductor_operation.htm

 

[crutschow]

The resistance of an inductor does not change with frequency (expect for that part affected by the skin effect at high frequencies). It's the reactance that changes. The reactance goes up with frequency and provides an impedance to AC current flow but, unlike resistance, it does not dissipate power.

 

[rag's]

Yup..i meant the reactance only..Sorry..

 

[MrAl]

Hello folks,

Some good points already have been mentioned and i was online so i
thought i would add a little to this thread...

Inductance and capacitance are both properties of the universe.
What this means more or less is that inductance is present even
in space itself, even when you dont have any wire at all.

But i think your question was more aimed at finding the difference between
a straight plain ol' wire and a coil of wire (inductor) and it's a good question
because both the wire that makes the straight wire AND the wire that makes
the coil could both be the same length, so why is the coil considered so
different?

The main reason i think has been already given, but i'd like to do a comparison
of the straight wire that is say 3 feet long and a coil of wire wound on
a 5/16 inch diameter wooded dowel but uses the exact same length of wire,
which is also 3 feet exactly.

This means we have two constructions: one is 3 feet of perfectly straight
wire and the other is 3 feet of coiled wire, wound on a 5/16 inch coil form.
We choose 5/16 inch diameter because the circumference is roughly
1 inch which is a nice round number to work with later.

When the straight wire is energized with a current, a magnetic field is created
around the wire and this field exists out away from the wire to some distance.
The field density around the first inch of the wire is about the same as the field
around the second inch of wire too. Thus, whatever field we find within the
first inch we find within the second inch too, and third inch and so on.
Now when the coiled wire is energized, the first inch works almost like
the straight wire, except because the wire is in a circle here it forces
the field to have a different shape around the wire. The new shape
compacts the field inside the center of the loop and so forces the field
to reach farther out the front and back of the loop rather than out
from the sides as with the straight wire. It's like squeezing a round
balloon with both hands...the ends bulge out more.
Now we come to the next inch of the coiled wire. This does the same thing,
and because its field also bulges out the ends it interacts with the
field from the first inch of coiled wire that also has the bulging field.
It just so happens that because the two loops are oriented side by side
with the current flowing in the same direction in both inches of the coil
the two fields reinforce each other which creates a stronger field.
Thus, the two turns of wire at the first two inches of the coil have a
stronger field than the first two inches of the straight wire.
With the coil, this action takes place for each turn of wire.
With the straight wire, there is no reinforcement of fields so the
field strength is less in the straight wire.

Now when the fields in both contructions collapse, a current is
induced into the wires, and this is what induction is. The current is
higher when the initial field intensity is higher, or to put it another way,
the higher the field the more induction takes place.

In this way we have more induced current in the coil then in the straight
wire so the whole idea turns out to be that we wanted to make a
bigger value inductor with the same amount of wire!
This lowers the cost considerably, so inductors are made with coils
rather than straight wires.
As a side effect, it seems easier to house a small coil of wire than a
very long straight piece of wire.

Another way of looking at the coil as compared to the straight wire is this...
The induced current in the wire is subject to a distance as well as the
field itself. The closer the wire is to the source of the field the higher
the current induced. Since a wire that is three feet long is, after all,
three feet long, its field is SPREAD OUT over a fairly great distance.
When the field collapses, each inch of field can only work on that one
inch of wire. But when the field in the coil collapses, all the coils are bunched up
very close to each other so that when the field collapses each turn of
wire is very close to the source of the field, so the induced current
is higher, which again means the coil of wire has a much higher
value of inductance than the straight wire.