Go Back   Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum > General Science Forums > Physics Forum
Register Search Today's Posts Mark Forums Read

Physics Forum Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Direct current "frequency"?

Direct current "frequency"? - Physics Forum

Direct current "frequency"? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 11-13-2007, 02:21 PM
Jeff
Guest
 
Posts: n/a
Default Direct current "frequency"?



I was reading some alternate physics information recently and came
across something that didn't quite sound right. The author was
quoting
from an article where the author of that article talked about
applying
a direct current of "high frequency but low pulses, in the auditory
range."

Correct me if I'm wrong, but you can only talk about frequence of
current when referring to alternating current, correct? I know you
can
pulse DC current but is there something I'm missing when the author
talked about the frequence of the direct current??

Reply With Quote
  #2  
Old 11-13-2007, 02:57 PM
PD
Guest
 
Posts: n/a
Default Direct current "frequency"?

On Nov 13, 8:21 am, Jeff <[Only registered users see links. ]> wrote:

Well, it's poor language, to be sure.
But on the other hand, AC specifically refers to a case where the
voltage and the current *change sign* during a cycle. But a pulse
which is always of one polarity can be considered DC, and so a
sequence of pulses can be DC and still have a frequency.

Reply With Quote
  #3  
Old 11-13-2007, 02:57 PM
PD
Guest
 
Posts: n/a
Default Direct current "frequency"?

On Nov 13, 8:21 am, Jeff <[Only registered users see links. ]> wrote:

Well, it's poor language, to be sure.
But on the other hand, AC specifically refers to a case where the
voltage and the current *change sign* during a cycle. But a pulse
which is always of one polarity can be considered DC, and so a
sequence of pulses can be DC and still have a frequency.

Reply With Quote
  #4  
Old 11-13-2007, 07:48 PM
dlzc
Guest
 
Posts: n/a
Default Direct current "frequency"?

Dear Jeff:

On Nov 13, 7:21 am, Jeff <[Only registered users see links. ]> wrote:

Like to your PC speaker, for example.


PD has the right response. Your entire computer runs on pulsed DC,
and all frequency means in "cycles per second". It does not have to
reverse (the definition of AC) current flow direction to have a
frequency. You could have an AC sine wave impressed on a DC bias, or
just switched DC. Describing how often the waveform repeats is all
that is required to describe it with a frequency.

You can even describe how often you change your oil with
"frequency"... ;>)

David A. Smith

Reply With Quote
  #5  
Old 11-13-2007, 07:48 PM
dlzc
Guest
 
Posts: n/a
Default Direct current "frequency"?

Dear Jeff:

On Nov 13, 7:21 am, Jeff <[Only registered users see links. ]> wrote:

Like to your PC speaker, for example.


PD has the right response. Your entire computer runs on pulsed DC,
and all frequency means in "cycles per second". It does not have to
reverse (the definition of AC) current flow direction to have a
frequency. You could have an AC sine wave impressed on a DC bias, or
just switched DC. Describing how often the waveform repeats is all
that is required to describe it with a frequency.

You can even describe how often you change your oil with
"frequency"... ;>)

David A. Smith

Reply With Quote
  #6  
Old 11-13-2007, 08:04 PM
Jeff
Guest
 
Posts: n/a
Default Direct current "frequency"?

On Nov 13, 1:48 pm, dlzc <[Only registered users see links. ]> wrote:

Thanks David and PD. I *think* that clears it up. What confused me was
his description of DC having a frequency AND a separate "pulse" rate
(which I assumed was the frequency when defined in terms of pulses per
second).

But if you can have an AC sine wave impressed on the DC bias, that
might be what he was describing, in addition to the pulse rate.

Thanks,
Jeff

Reply With Quote
  #7  
Old 11-13-2007, 08:04 PM
Jeff
Guest
 
Posts: n/a
Default Direct current "frequency"?

On Nov 13, 1:48 pm, dlzc <[Only registered users see links. ]> wrote:

Thanks David and PD. I *think* that clears it up. What confused me was
his description of DC having a frequency AND a separate "pulse" rate
(which I assumed was the frequency when defined in terms of pulses per
second).

But if you can have an AC sine wave impressed on the DC bias, that
might be what he was describing, in addition to the pulse rate.

Thanks,
Jeff

Reply With Quote
  #8  
Old 11-13-2007, 10:31 PM
dlzc
Guest
 
Posts: n/a
Default Direct current "frequency"?

On Nov 13, 1:04 pm, Jeff <[Only registered users see links. ]> wrote:
....
....

Yes, that is a problem when a reporter says "this is what this guy
said".


Actually, my guess is that only selected pulses from a high frequency
pulse train were "duplicated" on this other circuit, giving actually
an audible frequency with a very short rise and drop time.

In other words, I think the quote is pure technobabble, and you were
right to be confused. But I am just a MechE.

David A. Smith

Reply With Quote
  #9  
Old 11-13-2007, 10:31 PM
dlzc
Guest
 
Posts: n/a
Default Direct current "frequency"?

On Nov 13, 1:04 pm, Jeff <[Only registered users see links. ]> wrote:
....
....

Yes, that is a problem when a reporter says "this is what this guy
said".


Actually, my guess is that only selected pulses from a high frequency
pulse train were "duplicated" on this other circuit, giving actually
an audible frequency with a very short rise and drop time.

In other words, I think the quote is pure technobabble, and you were
right to be confused. But I am just a MechE.

David A. Smith

Reply With Quote
Reply

Tags
current , direct , frequency


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
what is peptide direction of migration in direct current? mohamed Peptide Forum 0 07-19-2009 01:17 AM
Direct current "frequency"? Jeff Physics Forum 0 11-13-2007 02:21 PM
Proposition for performing a series of electromagnetic experiments Hamid.V.Ansari@gmail.com Physics Forum 22 09-16-2007 02:52 AM
Proposition for performing a series of electromagnetic experiments Hamid.V.Ansari@gmail.com Physics Forum 0 09-05-2007 05:41 AM
Logical justification of the Hall effect h_v_ansari@yahoo.com Physics Forum 1 10-19-2006 07:23 PM


All times are GMT. The time now is 12:47 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 2005 - 2012 Molecular Station | All Rights Reserved
Page generated in 0.16274 seconds with 16 queries