- #1
Pushoam
- 962
- 52
Theoretically speaking, does the frequency of em wave range from 0 to infinity?
Well it can't be zero. It can approach zero, though. It also can't be infinity (being that infinity is not a real number). It can approach infinity, though.Pushoam said:Theoretically speaking, does the frequency of em wave range from 0 to infinity?
jedishrfu said:I think its limited by the Planck length when you go toward 0 and limited by the size of the universe as you go toward infinity.
https://en.wikipedia.org/wiki/Electromagnetic_spectrum
In classical physics of the 19th century, it was believed to be continuous going from 0 to infinity.
Blop said:Do you mean that it's range is infinite from a whole numbers perspective? Because something's frequency can't literally be 'infinity'
Blop said:Do you mean that it's range is infinite from a whole numbers perspective? Because something's frequency can't literally be 'infinity'
If we uniformly accelerate an electron and then allow it to continue at constant velocity, the radiated E-field would seem to be unidirectional, and hence it must possesses a zero frequency component.anorlunda said:It is more of a question of semantics. Neither zero nor infinite wavelengths are practically possible. But there is no theoretically defined 0<limit or limit<infinity.
So I think the best way to say it is that the limits are practical, not theoretical.
tech99 said:If we uniformly accelerate an electron and then allow it to continue at constant velocity, the radiated E-field would seem to be unidirectional, and hence it must possesses a zero frequency component.
AlphaLearner said:Does a wave exist with 0 frequency? If so, should it be just a wave pulse?
Based on a picture in book 'Fundamentals of physics', wave pulse does not look like as you said.Drakkith said:No, a wave pulse consists of many frequencies that interfere with each other to form the pulse. A wave with zero frequency can't be called a wave at all because nothing is changing. There is no oscillation, no vibration, nothing.
Yea... the first one sounds like a wave can exist with 0 frequency (case of DC) I don't know the second.NTL2009 said:In electronics, a "zero frequency" signal would be considered DC. So for EM, would a stationary magnet be analogous?
AlphaLearner said:Based on a picture in book 'Fundamentals of physics', wave pulse does not look like as you said.
NTL2009 said:In electronics, a "zero frequency" signal would be considered DC. So for EM, would a stationary magnet be analogous?
Drakkith said:You can probably think of it like that, but I would still say that a wave with zero frequency isn't a wave at all.
NTL2009 said:Would a stationary magnet be analogous to that thought?
Thanks for clarification, so there is frequency even in wave pulse.Drakkith said:Sure it does. The different frequencies interfere with each other such that they sum to zero or near zero everywhere outside of the pulse.
AlphaLearner said:Is the frequency in electric current is caused due its patterned flow in a conductor, like in AC current, energy flow half - cycle up and then half cycle down creating to and fro motion treating as wave but not the actual frequency at which electrons vibrate when the disturbance/energy flow through conductor... Am I right anywhere?
AlphaLearner said:And what's the difference between a signal and a wave?
AlphaLearner said:Thanks for clarification, so there is frequency even in wave pulse.
Does that mean electrons literally displace and flow?Drakkith said:electrons are always whizzing about in all directions and current flow is the net flow of electrons in a direction.
Since particles in EM wave are too small and a wave of size of universe means each particle should show enormous displacement stably without disturbance, I think it is impossible.jedishrfu said:limited by the size of the universe as you go toward infinity.
AlphaLearner said:Does that mean electrons literally displace and flow?
AlphaLearner said:Rate of oscillation in what? The whole bunch of flowing electrons? That whole bunch move back and forth as they flow just like a ship sailing back and forth in harsh waters? Then some people say frequency as cycles/sec. Can it be anywhere linked to this?
Drakkith said:The electrons themselves aren't vibrating back and forth at this frequency.
Thanks for help, Understood what you have said and satisfied.Drakkith said:The electrons in the conduction band of a conductor are constantly moving about within the conductor in random directions and velocities. The electric field of an AC voltage source merely gives this random motion a small net velocity. In other words, more electrons move move one way past a point in a wire over time than in the other direction leading to a net flow of current in the circuit.
The net flow is the sum of all the different velocities and it is this net flow that oscillates in direction and magnitude. Any single electron is not oscillating back and forth.
davenn said:I have always understood that they are
and to confirm my thoughts I had to go google searching and found at least 4 sites that confirm that the electron/charge IS oscillating back and forward at the freq of concern
do you have something to the contrary ?
AlphaLearner said:In it he told to imagine flowing electric current as a people standing in a queue at box office for movie tickets and just told, If the person behind the queue pushes the person in front of him, he falls on another and like that whole queue gets knocked down. Does he mean electrons won't flow but that disturbance flow?
AlphaLearner said:And I think its a better idea to start a new thread and discuss much upon this.
On it.Drakkith said:I recommend make a new thread Indeed.![]()
Drakkith said:Well, my textbook, Semiconductor Physics and Devices, by Donald A. Neamen, gives a short explanation of electric current on pg. 74 and describes drift current as the summation of all the individual electrons velocities, each of which is much larger than the drift velocity that gives rise to current.
Several wikipedia articles also support this. See the following links:
https://en.wikipedia.org/wiki/Drift_velocity
https://en.wikipedia.org/wiki/Electric_current#Metals
Also, see page 3 here: http://alan.ece.gatech.edu/ECE3080/Lectures/ECE3080-L-7-Drift - Diffusion Chap 3 Pierret.pdf
The average instantaneous velocity is extremely large. One of wiki's articles gives a velocity of roughly 106 m/s. In comparison, drift velocity is on the order of cm/s or less.
This analogy is mainly given for studying wave motion in part one of his series.AlphaLearner said:In it he told to imagine flowing electric current as a people standing in a queue at box office for movie tickets and just told, If the person behind the queue pushes the person in front of him, he falls on another and like that whole queue gets knocked down.
davenn said:There may well still be a general drift of electrons in an AC (RF) circuit I'm not 100% sure, I have never seen anything to back that up
maybe some one can confirm or deny it. Even if there is, it doesn't mean that in an AC signal the electrons are not oscillating about a point
at a given freq be it 50/60Hz mains or in a 10 GHz microwave RF circuit