Capacitance, Inductance, Reactance, Resistance, Impedance

Think of inductance or reactance as a frequency dependant resistance. Or AC resistance if you like.
You just need to understand the effects, calculations and relationships.
The actual fundamentals of how and why these things work aren't actually fully understood (IMHO) they can be calculated and described and that's enough for all practical purposes. Interaction of electric & magnetic fields is probably a good place to start...
If you delve into the physics of it you can just question each layer of explanation and end up at the quantum level and probably ask question beyond our current understanding.
Is explanation and understanding the same thing? Discuss.

If you want a better explanation then you must ask a more concise question, E.G what is inductance.
Del

A good mechanical analogy is perhaps inertia?
To change or move anything requires energy, inductance and capacitance have extra 'inertia'.
AC being constant change is subject to these effects.
Del

Del, Glad that you've responded. The confusing part is understanding the nature and actions of X,R,L,C,Z. From what i understand about R is that it is inbuilt in an element. Every element has some resistance, some more than others. So a conductor wire would naturally have resistance. Hence the current passing the conductor would be affected. Is X also inbuilt in the conductor wire???

Can you also provide easy to understand info which I might read on the WWW.

From what you've just stated can i assume that inductance does not incur on a single conducting wire (in straight physical condition - assume a straight line). But rather on a coil of wire (circular twisting of wire). If that single wire is wound in to a coil and current is passed through such a wire coil (present physical condition) Then the inductance would be present. How?? I have assumed that due to storage of electromagnetic field. Inductance is basically storage of electromagnetic field within the coil. In fact inductance is a good thing. Right. It protects the conductor from Short circuits and also acts as an opposing force.

Is my understanding correct? if so What about capacitance and the rest?

Del Kindly disregard this point "From what you've just stated can i assume that inductance does not incur on a single conducting wire (in straight physical condition - assume a straight line)."

Infact there would be inductance in a straight wire as well but not as much compared to a coiled wire.

From what you've just stated can i assume that inductance does not incur on a single conducting wire .
I that case you didn't read my post very carefully.
Re-read line one s-l-o-w-l-y

Oh then dissregard this response...
Del

Simple Explanation

Inductance:- It is a "Characteristic" of an "Electrical Circuit/conductor". Hope were clear up till now. . Now then. The inductance is a characteristic of an electrical circuit/conductor "WHICH OPPOSES" the "Starting", "Stopping" or or or any "CHANGE" in the "Value" of the "CURRENT".

Now let me us assume that you are pushing a car. OKAY. The initial or Starting push is the HARDEST and so is the Stopping Push. Mean while pushing a moving car is easy. This property is called INERTIA. Intertia is a property of mass which opposes change in VELOCITY. This is what inductance does to the Current. What INERTIA does to a CAR is SIMILAR to what INDUCTANCE does to the CURRENT.

When talk about Inductance and Current together. Inductance is storage of energy in magnetic field.

BTW unit of Inductance is L (Henry)

Capacitance:-

Similar to Inductance. Opposes change in VOLTAGE. storage of energy in electric field.

The electrons are lazy snobs and it takes a bit to get them moving. Once they get moving they hate to stop.

READ ELECTRICAL TECHONOLOGY TEXT BOOK OF -EDWARD HUGES,OR HENRY COTTON-

ELECTRICAL TECHONOLOGY IS TAUGHT IN THE FIRST YEAR CLASSES,IF YOU READ THIS BOOK PROPERLY AND HAVE BASIC KNOWLEDGE OF MATHS AND CALCULUS YOU WILL UNDERSTAND .

Dear guest,

Inductance is the property of opposing a change in current passing through a conductor . 1. The first thing to understand is that a conductor subjected to a voltage difference and carrying current generates a magnetic field around it (discovered by Faraday). As long as the current is constant the magnetic field measured at various points around it remains constant. The magnitude of the field is proportional to the current and also reduces with the distance of the point from the conductor according to a law. 2. When the current changes with time in a wave form such as in an AC supply, the magnetic field also changes with time. The changing magnetic field generates a voltage in the conductor which opposes the change. Thus it's effect is similar to inertia. In other words it creates a resistance in the circuit through creation of a voltage that is opposite to the applied voltage. This resistance is maximized in a coil form with a soft iron core.

When a current flows in a conductor, it creates a magnetic field round the conductor. This magnetic field will be changing as the current is building up to its normal peak value. due to this variation, a voltage/current is induced in the conductor and in the opposite direction from the original flow. When the current becomes steady, there will be no more induced opposit current because the magnetic field is no longer changing or varying. This is the DC status where ther is no more Inductance to take care of but pure resistance.

For AC current, the field is constantly varying and therefore the phenomena of the induced voltage/current carries on. This is what causes the inductance to be present and of significant value in any AC and the higher the frequency the higher the inductance value because of the speed at which the field if varying.

In a coil, the effect is enhanced and amplified because of the density of the field in a smaller volume (winding, compact...).

For Capacitance, a similar reasoning can be adopted but now the phenomenon is in opposite direction: Instead of a magnetic field creating an opposed voltage, the capacitor acts as a short circuit at the beginning of the establishment of the current until it gets full. For DC, it becomes like an open circuit but for AC it will start to contribute to the receding current value when it changes direction of flow. Then again acts as a short when the AC reverses. For a single conductor, the capacitance value depends on its proximity to other conducting surfaces that will form a natural capacity... In a coil, there will be a capacity value due to the compactness of the different layers...

To go further, you need to get a specialised book on the subject or a course in basic Electricity...

If you want a mechanical simulation to the phenomena, you imagine 2 springs anchored at one end, opposite each other, and linked on the other end (center point of both). Now try to move the center joined point towards either end (anchored), then try to go the opposite way. keep doing that: One spring will be opposing while the other will try to enhance. This gives an idea (even if not 100% correct at least a feeling) of the reactance which is due to a combination of a coil (Inductance) and a Capacitor (Capacitance) in a circuit. An Impedance will also take in consideration the pure resistance.

RLC Circuits are either inductive or capacitive. They have a resonant frequency. Electronic texts have all the formulas to derive the values for R, L, C, F, and their impedences (X or Z). A wire has inductance, which comes into play at higher frequencies, and that is why inductors are made from them - due to the magnetic field created in a conductor when current goes through it. When a voltage is applied to an RLC circuit, voltage lags current in the capacitor, and current lags voltage in the inductor, hence the impedence and reactance formulas used to calculate the above values. The formula you are using above is incorrect - consult a textbook. The reactance (X) in the conductor is dependent on the frequency. It is the result of outer valence electrons in the conductor transferring from one atom to the next, typically at the speed of light. I hope this helps.

"It is the result of outer valence electrons in the conductor transferring from one atom to the next, typically at the speed of light."

The speed electrons move is nothing even close to the speed of light in any conductor even a super conductor.

In a super conductor the electric field moves at the speed of light but as soon as you start adding the resistance, capacitance and inductance you have in a real conductor the propagation speed can be as slow as half the speed of light.

In fact, anything that has a rest mass, which an electron has, can never travel at the speed of light because its mass would become infinite and therefore require an infinite amount of energy to accelerate it to light speed.

Sorry, but the propagation speed of the field or current etc is at the speed of light even though the electrons are not travelling at that speed!

I know they taught you in school that electricity travelled at the speed of light but in the real world it doesn't.

An electromagnetic field will propagate at speed of light along a superconductor. However, when you start to add in the effect the capacitance between the conductor and ground, the inductance along the conductor, the resistance along the conductor and the conduction to ground, the speed at which the effect propagates is considerably less than the speed of light.

What you need to do is look at a piece of wire as a series of LRC circuits connected in a chain like that in the image below. I've only shown 5 LRC circuits but a roughn approximation of a cable can be modelled using 10. The more you add the more accurate the model.

When you send a signal in one end it gets modified by the first LRC circuit which then feeds into the second where it gets modified again and so on. The end result is that the signal not only doesn't propagate along the conductor at the speed of light but becomes distorted along the way.

The propagation speed depends very much on the type of conductor, for example solid polyethylene dielectric cables have a propagation speed of ⅔ c or 200,000 kms^-1, while really cheap telephone cables it can be less than ½ c.

The whole thing can become very complex, particularly when you start to look at multiple conductors, but it's worth having a look at the Wikipedia articles entitled Transmission Line and Wave Propagation Speed.

"I know they taught you in school that electricity..."

That is uncalled for since you do not know my credentials in the first place.

On the subject at ahnd: I think I can understand what you are saying even though I don't have to be an expert in "transmission Lines theories". BUT if you come to think about it YOu could say that the Propagation Speed is constant AND the PATH is the one being varied, getting longer due to the Capacitance / Reactance of the line... ? After all the Maths are a tool to try and match the realities with some theories to make life easier for the designers and problem solvers. It does not mean that we really can be ABSOLUTELY adamant about the phenomenae....

"That is uncalled for since you do not know my credentials in the first place."

Fair enough and it wasn't meant as an indictment of you so I apologize, but I would hazard to say that somebody eroneously taught you that electricity travells at the speed of light.

"the Propagation Speed is constant AND the PATH is the one being varied, getting longer due to the Capacitance / Reactance of the line... ?"

I don't think you can say that the length of a piece of wire is longer because it's not a superconductor and has capacitive, inductive and conductive properties. If you have a piece of wire that is 10 metres long then the signal needs to travel 10 metres.

If you can get hold of the following equipment:

• 300 m 2 pair telephone cable or something similar
• Square wave signal generator
• 2 channel oscilloscope
• 600 Ω resistor

you may like to try this experiment.

Using one pair of the cable connect the signal generator to one end and the 600 Ω resistor to the other end. The resistor acts as a load and prevents the signal from being reflected.

Now connect channel 1 of the oscilloscope to the signal generator end of the cable and channel 2 to the other end where the resistor is.

Now if the signal travelled at the speed of light which is 3 x 10⁸ ms^-1 then it should take

300 m / 3 x 10⁸ ms^-1 = 1 x 10^-6 seconds = 1 ms

to travel the length of the cable

So set up the signal generator so that it generates a 10 μs long pulse every 200 ms and the oscilloscope to 100 μs per division and trigger off channel 1.

What you should see is the input signal on the top channel and output at the bottom with the output delayed by the time it takes the signal to travel along the cable. If the channel 2 signal is more than 10 division later than the channel 1 signal then the signal is travelling slower than the speed of light.

It's going to depend on the cable but for the usual cheap 2 pair telephone cable I would hazard to say that the delay will be more like 20 divisions or 2 ms which corresponds to around half light speed.

You could try this with any multi core cable, for example CAT5 and you can increase the distance the signal needs to travel by sending it down one pair, back another and so on until you have run out of pairs.

It's worth doing this experiment for yourself because firsthand knowledge is always best but if you can't you will just have to believe that electricity doesn't travel along a piece of wire at the speed of light.

Thank you for the explanations.

What I was proposing is not that the length of wire physically extends but rather, since you can make it equivalent to a series of Capacitors in parallele..., that the wave will seem to have an equivalent longer distance to travel: filing a capacitor then moving to the next... looks like delays... and even if we assume for the maths that the propagation speed is constant, it takes longer because of the delays at each stage as put by you.

Any way, thanks.

That's precisely what's happening.

The LRC ladder is however an approximation that is used to physically model the cable and ten rungs is usually good enough to model a cable in the laboratory. However, you can build a more accurate mathematical model using calculus which is analogous to creating a ladder circuit with an infinite number of rungs.

All of you who have responded to my query. I thank you for your guidance.

After your words I have fully understood inductance and Capacitance.

If you are also willing,can you kindly explain about Impedance and Reactance as well.

Sincerely,

Biologist

Impedance is effectively, resistance to current and voltage flow, but in an AC circuit, and the unit of measure is OHMS.

In a DC circuit, it is simply called Resistance.It is also measured in OHMS.

Reactance comes in two types :Capacitive(Xc) and inductive (Xl).And, alas, it is also measured in ohms.

The difference is of course dependent on the circuit,with IMPEDANCE being the TOTAL resistance of the circuit due to ALL forms of resistance: resistive, capacitive, and inductive.

...a visualized vector analogy, just think "3-4-5 right-triangle," using the equation:

Z = SQR[ R² + (XL-XC)²]

...where:

R = DC resistance (Horizontal axis) ...no phase angle.

XL = AC inductive reactance (Vertical axis UP)...XL = 2ΩfL

XC = AC capacitive reactance (Vertical axis DOWN)...XC = 1/(2ΩfC)

Z = AC impedance (the vector combination of Horizontal (DC) and Vertical (AC) oppositions)

...for example, think "3-4-5 right-triangle," where: Z = 5 and R = 4 and (XL-XC) = 3, ie:

Z(5) = SQR[ R(4)² + X(3)² ]

HINT: associate the "DOWN" direction with the XC's "reciprocal" function, ie: below the vinculum.

In my quick read through I didn't notice the terms REAL and IMAGINARY. Resistor "resistance" has a mathematically real number and power is consumed. Reactive "resistance" has a mathematically imaginary number and power is not consumed (by the IDEAL reactive element). This all tends to get complicated as you get deeper into it. But, you will get to a point where you need to remember that ideal capacitors and ideal resistors do not consume power, but ideal resistors do.

If you keep going with this you will start to find the textbook not matching the real world. All "real world" components have resistance, capacitance and reactance. We normally don't like it, but that is the way it is.