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# Require help with electron flow in a circuit, and when the wavelength is much longer than the size of the circuit.

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#### linuscomex

##### Junior Member level 3
electron flow in circuit, when wavelength is very longer than size of circuit ?

1--My first question is: when signal with low frequency such as 100khz the wavelength of that is 5 kikometer that means between high and low voltage must be 5 kilometer .so when signal propagate by electron in short circuite (size of circuit is very small than wavelenght)how does electron flow in circuit and 5 kilometer space between the hight and low voltage produce in short circuit???is it true the wavelength of the signal that means:distance of electron travel to reach the first point? If it is true so the signal with 5 kilometer wave lenght produce complete when electron travel 5 kilometer and thus structure repeat.

2-when the size of circuit very small than if wavelength ghen for analysis the circuit we use Kirchhoff's circuit laws Whay the voltage and current in this circuit not change?but in high frequency change I guess in low frequency that wavelength very big than size of circuit the electron have Enough time to reach end of wire and Enough to produce a cycle of signal Because the electron move is very fast and wavelength is very long that the cgarge of electron Enough time to travel on circuit and produce a cycle of wave before next cycle produced. I guess this 2 reason for not change current in length of wire and voltage in first and end of wire is same.is it true?

I know transmission line theory how work. but I dont undrstand whay voltage and current is same in all of the wire lenght,when frequency low and wavelength is very long of size of circuite? in transmission line and maxwell theory happen stand wave because the wave length in antenna and transmission line is proportional lenght of conductor and electron charge not enough time to reach end of conductor befor a cycle if sine wave ended so the electron charge reflected back and stand wave happen this reason of whay antenna work like resonator and radiate with high amplitude. In transmission line and antenna the voltage and charges electron in 1cm and 3cm of wire length is difference because the frequency is very high and wavelength proportional to size of length wire and when electron charge flow in wire because of wavelength the cgarge if electron difrrent in length of wire and no time to reach end of wire and this reason the voltage in length of wire is difference unlike lumbd circuit that voltage same in all length of wire. I dont undrestand this phenomenon how to happen in low frequency and very long wavelength which makes voltage not changed in lenght of wire? is it true the sentence Thanks bro.

When wavelenght is very long that length of circuit and open clos loop the current is zero because all voltage in length is same and no potential make in circuit .
But when wavelenght is short and length of circuit or electrical length same it in open wire have current.
whay diffrence between this state?

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

Welcome linuscomex,

You've asked some great questions. The difference between electrical circuits that are electrically small as compared to those which are electrically large is the reason why the fields of microwave or "RF" engineering exist.

The basic, unfortunate truth is that circuit theory as taught in introductory courses is only correct at DC (0 Hz). When a time-varying source is introduced, the approximation is usually made that the speed of propagation through the circuit is infinite. In this case, an excitation at one port can instantaneously effect a change at other ports, no matter what is in between them. However, from Maxwell's equations, we know that AC voltages and currents travel as waves, whose values change as a function of space and time, and have a finite propagation velocity.

1) The wavelength of a signal in an unbounded medium can be 5 km. If an electrical circuit (lets say 10 cm long) is being excited by this frequency, you can imagine placing this circuit beside an image of this wave (which, for the sake of argument let's say represents a voltage wave). The value of this wave will not change much over the length of this circuit, since the circuit is so small compared to the wavelength. Therefore, we say that the circuit is electrically small, and you can most likely safely analyze the circuit without taking into account propagation velocity (phase change over distance). The electrons in this circuit see effectively the same voltage everywhere (as they would at DC), such that the electrons at any point in the circuit are moving in the same direction. However, this direction is still oscillating at the exciting frequency.

2) The circuit laws are correct, at any given point. The approximation of a "point" just becomes larger with decreasing frequency, such that at DC we can refer to any conductor as a "point" on a circuit diagram. In high frequency (small wavelength) systems, if we were to superimpose the voltage wave on the circuit, we would see that there are now multiple wavelengths inside the circuit. This means that electrons at different points are now moving in different directions. As such, the circuit needs to be analyzed taking into account phase shift (voltage change) with distance. I'm sorry, I don't understand what you're asking about the wire in this case.

Hope this helps!

linuscomex

### linuscomex

Points: 2
Re: how electron flow in circuite, when wavelenght is very longer than size of circui

Thanks for response.
Doease it my reason true??

I explain my reason for 2 question in first post is it true?

In your response you tell in short electrical circuit voltage and current not change because wave lenght very big buy can you tell me how electron flow in circuit if ac current.???
if ac current flow in circuit the electron carry charge in circuit .
Please tell me how ac current not change in lenght of circuit in short circuit?
How a period of ac current produced and flow by electron in circuit While we know the period of ac current wave have 5 kilometer because frequency is 100 khz while the length of circuit 10 cm????

Witch part of my questions not understand?

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

no time to reach end of wire

Not an answer to your question, but the electrons travel slower than current propagation.
https://en.wikipedia.org/wiki/Speed_of_electricity

The change of voltage in AC (=> frequency) is not directly related to propagation delay on the line, so it is difficult to understand what your question is.

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

Not an answer to your question, but the electrons travel slower than current propagation.
https://en.wikipedia.org/wiki/Speed_of_electricity

The change of voltage in AC (=> frequency) is not directly related to propagation delay on the line, so it is difficult to understand what your question is.

whay in circuit that wavelenght very long than lenght of circuit AC current and voltage not change????
when you measure current of circuit by Oscilloscope show you complete AC current and you put probe on evry where of circuit the current not change. whay current not change and how electron propagate that the Oscilloscope can show full wavelenght of ac current (ac signal frequency 100khz and wavelenght 5 kmeter) and how 5kilometer wavelenght show by Oscilloscope?

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

Wavelength of 100kHz signal is 3000m. Comparing 10cm of circuit dimension and wavelength of 3km you will need extraordinary oscilloscope whose precision maybe compared to a crystal oscillator precision of 3.333333e^-5 to just notice anything. Impossible because oscilloscopes are 1% precise. At high enough frequencies where this problems occur we use other instruments to check or tune circuits.
BTW 1% precision satisfies usual circuit electrical tolerances more than enough.

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Re: how electron flow in circuite, when wavelenght is very longer than size of circui

If it is true so the signal with 5 kilometer wave lenght produce complete when electron travel 5 kilometer and thus structure repeat.

No. Somehow you misunderstand things, and mix different topics. You can generate very low frequency signals with very small circuits. No long lines (or time delay) needed.

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

No. Somehow you misunderstand things, and mix different topics. You can generate very low frequency signals with very small circuits. No long lines (or time delay) needed.
how do you generate a sin wave 100khz in small circuit?
in 100 khz wavelenght is 5 kilometer(do you know what is wavelenght?)( the wavelenght is distance between two point of maximum the sine wave ) how 5kolometer distance generate in 10cm circuit??????

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

how do you generate a sin wave 100khz in small circuit?

Using an LC oscillator.

in 100 khz wavelenght is 5 kilometer(do you know what is wavelenght?)

Yes, I am a professional RF engineer for 25 years. You seem to be confused what wavelength is and when/where it matters.

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

Wavelength is just another term describing frequency.

wave length=speed of light/frequency

Which term you will use depends on need to present physical dimensions. Usually at microwave frequencies where wavelengths are in order of decimeter or smaller. Ham operators cal 144MHz frequency band a two meter band(less words).

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

Using an LC oscillator.

Yes, I am a professional RF engineer for 25 years. You seem to be confused what wavelength is and when/where it matters.

the wavelenght is distance between two point of maximum the sine wave ) how 5kolometer distance generate in 10cm circuit??????
do you know whay in short circuit that diameter of circuit is very small than wavelength, the voltage not change in circuit an you can use Kirchhoff's law???

Re: electron flow in circuit, when wavelength is very longer than size of circuit ?

While you are generating 5km signal in 1cm circuit all 5km is in your imagination and circuit outputs 60.000kHz sinewave signal.
When you whistle 1kHz tone it's wave length is about 0.333m.

Re: how electron flow in circuite, when wavelenght is very longer than size of circui

the wavelenght is distance between two point of maximum the sine wave

If you have a wave in free space, the period is one wavelength.

how 5kolometer distance generate in 10cm circuit??????

You do not generate any distance in the circuit. You do not need to create a standing wave. Your understanding of the meaning of the wavelength is totally confused. If your computer soundcard generates a 1kHz tone, it just changes the voltage with 1kHz frequency. This is about changing voltage levels/polarities, not about sending electrons to a long journey on long wires and waiting until they come back. Just change the voltage and here's your frequency.

It is true, you will not see wavelength effects on a small circuit. You are very near the DC case, where all voltages at different points in the circuit change with almost no delay (=in phase).

The wavelength can be calculated, but has no practical meaning because all circuit length is small, and standing wave effects and transmission line effects are too small to notice.

do you know whay in short circuit that diameter of circuit is very small than wavelength, the voltage not change in circuit an you can use Kirchhoff's law???

There is no exact limit. We start to see transmission lines effects when the line is NOT short compared to the wavelength. Or speaking about time domain signals (pulses), we start to see transmission line effects when the travel time on the line is NOT short compared to the pulse rise/fall time.

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Re: how electron flow in circuite, when wavelenght is very longer than size of circui

If you have a wave in free space, the period is one wavelength.

You do not generate any distance in the circuit. You do not need to create a standing wave. Your understanding of the meaning of the wavelength is totally confused. If your computer soundcard generates a 1kHz tone, it just changes the voltage with 1kHz frequency. This is about changing voltage levels/polarities, not about sending electrons to a long journey on long wires and waiting until they come back. Just change the voltage and here's your frequency.

It is true, you will not see wavelength effects on a small circuit. You are very near the DC case, where all voltages at different points in the circuit change with almost no delay (=in phase).

The wavelength can be calculated, but has no practical meaning because all circuit length is small, and standing wave effects and transmission line effects are too small to notice.

There is no exact limit. We start to see transmission lines effects when the line is NOT short compared to the wavelength. Or speaking about time domain signals (pulses), we start to see transmission line effects when the travel time on the line is NOT short compared to the pulse rise/fall time.

thank you my friend.

when 300khz sine wave propagate in circuit a period of signal produce by electron carry charge is it a period of signal lenght 3 kilometer? like lenght of transmission line that propotional wavelenght

Re: electron flow in circuit, when wavelength is very longer than size of circuit ?

300kHz sine wave propagate in circuit with speed of light. In certain point of circuit all you can do is to count number of periods in a second of time. This is how frequency is measured.
300MHz sine wave signal through mismatched line will have voltage peaks distributed along line on distances exact wave length of that frequency. A sloted line was used for measuring voltage along line.
https://en.wikipedia.org/wiki/Slotted_line

Re: electron flow in circuit, when wavelength is very longer than size of circuit ?

300kHz sine wave propagate in circuit with speed of light. In certain point of circuit all you can do is to count number of periods in a second of time. This is how frequency is measured.
300MHz sine wave signal through mismatched line will have voltage peaks distributed along line on distances exact wave length of that frequency. A sloted line was used for measuring voltage along line.
https://en.wikipedia.org/wiki/Slotted_line

thank for response.
but i dont measure voltage and vswr in tranmission line.
i want to know real meaning of wavelenght. is that distance between two pint of sinewave ? in transmission line and antenna wavelenght very important and lenght of antenna is part of wavelenght because the lenght of wavelenght very important to propagate electron energy in antenna. a explain by example:

Suppose the sine wave (Asinwt) Placed in circuit.In the picture below you can see mode. pleause answer my questions

Re: electron flow in circuit, when wavelength is very longer than size of circuit ?

You have drawn a conductor. Now you apply a voltage to the conductor, with 300kHz frequency. This means that the voltage at the source changes over time. But there is only very small voltage difference to another location on the wire that is some meters away. Voltages at both locations is almost identical, because the distance is very small compared to the wavelength.

Now go to a much higher frequency, 300MHz for 1m wavelength. In this case, the wire is not short compared to the wavelength, and the voltage at each location on the wire is different. If you measure at the same time at two points that are 1/2 wavelength = 50cm away, you will see opposite polarity (180° phase shift). At t=0 the source has 1V * cos(0°) = 1V and the point 50cm away has 1V * cos(180°) = -1 Volt. Different volates at different locations, at the exact same point in time.

But at low frequency 300kHz = 1km wavelength, the difference in phase between two points that are 50cm away is only 360° x 0.5/1000 = 0.18° and there is almost no voltage difference. At t=0 the source has 1V * cos(0°) = 1V and the point 50cm away has 1V * cos(0.18°) = 0.999995 Volt. Almost exactly same voltages on the conductor at all locations, so very similar to the DC case.

linuscomex

### linuscomex

Points: 2
Re: electron flow in circuit, when wavelength is very longer than size of circuit ?

linuscomex, imagine you have MW receiver for 500m-200m wave lengths (600kHz-1500kHz). How big must be receiver according to your expectations? Are it's measures elastic to cover all wave lengths?

Re: electron flow in circuit, when wavelength is very longer than size of circuit ?

You have drawn a conductor. Now you apply a voltage to the conductor, with 300kHz frequency. This means that the voltage at the source changes over time. But there is only very small voltage difference to another location on the wire that is some meters away. Voltages at both locations is almost identical, because the distance is very small compared to the wavelength.

Now go to a much higher frequency, 300MHz for 1m wavelength. In this case, the wire is not short compared to the wavelength, and the voltage at each location on the wire is different. If you measure at the same time at two points that are 1/2 wavelength = 50cm away, you will see opposite polarity (180° phase shift). At t=0 the source has 1V * cos(0°) = 1V and the point 50cm away has 1V * cos(180°) = -1 Volt. Different volates at different locations, at the exact same point in time.

But at low frequency 300kHz = 1km wavelength, the difference in phase between two points that are 50cm away is only 360° x 0.5/1000 = 0.18° and there is almost no voltage difference. At t=0 the source has 1V * cos(0°) = 1V and the point 50cm away has 1V * cos(0.18°) = 0.999995 Volt. Almost exactly same voltages on the conductor at all locations, so very similar to the DC case.

thank you bro.

pleause show again my image and answer below question

hpw possible full period of sine wave produced in lenght 10 cm??? pleause show dot 1

full sine wave need 3 kilometer lenght to produced

Re: electron flow in circuit, when wavelength is very longer than size of circuit ?

full sine wave need 3 kilometer lenght to produced

No.

No.

No.

I give up, this makes no sense because you don't read answers.

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