Most Current Travels 4 Inches per Second

[Globemaker]

Electrons in a wire commonly travel much more slowly than most people
expect. A simple calculation will show that in many common wires in
houses, radios, and computers, the average speed of current flow is
less than one meter per second. That slow current carries signals at
more than 20% of the speed of light in a vacuum. Details at 11...

 

[Bob Masta]

On Sun, 8 May 2011 08:05:43 -0700 (PDT), Globemaker
<alanfolmsbee@cabanova.com> wrote:

Electrons in a wire commonly travel much more slowly than most people
expect. A simple calculation will show that in many common wires in
houses, radios, and computers, the average speed of current flow is
less than one meter per second. That slow current carries signals at
more than 20% of the speed of light in a vacuum. Details at 11...

.... and in AC circuits, the electrons just go back and forth
and never make net progress down the wire!

The teaching analogy I like best for the slow drift velocity
but high information speed is " marbles in a pipe". I made
such a model to demonstrate to my (then) young nephew, using
a foot of 7/8 PVC pipe, filled with same-colored marbles.

Use a long rubber band from one end of the pipe to the other
to hold the marbles in place when you turn it vertical.
Prepare this ahead of time, so the subject(s) don't know
what you've done, and present it like magic trick: You
gently push a (same-colored) marble into the bottom of the
pipe (past the rubber band) and it appears to instantly pop
out of the top! (Shoots up in the air a bit, when it
overcomes the tension of the rubber band.)

Do this a few times, then push a different-colored marble in
the bottom. Hmm, an original-colored marble pops out the
top. Keep pushing in new marbles, until finally the odd one
pops out.

Explain that this is like electricity, where one electron
going into a wire pushes all the others along so that a
different electron "instantly" pops out the other end.
Since all electrons are interchangeable, it only *seems*
that they move with great speed through the wire.

(Follow up: Years later, my nephew is now preparing to
become an auto mechanic... so maybe this great teaching tool
didn't stick. But at the time, he sure seemed to enjoy all
the marbles bouncing around the room!)

Best regards,


Bob Masta

DAQARTA v6.01
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
Frequency Counter, FREE Signal Generator
Pitch Track, Pitch-to-MIDI
Science with your sound card!

 

[Globemaker]

On May 8, 11:05 am, Globemaker <alanfolms...@cabanova.com> wrote:

Electrons in a wire commonly travel much more slowly than most people
expect. A simple calculation will show that in many common wires in
houses, radios, and computers, the average speed of current flow is
less than one meter per second. That slow current carries signals at
more than 20% of the speed of light in a vacuum. Details at 11...

1 amp DC = 1 coulomb per second = 6.2 x 10 ^ 18 electrons / sec = Q/
sec

Q= 6.2 x 10 ^ 18 electrons in a coulomb

copper density of conduction electrons = 8.5 x 10 ^22 / cc = d

wire segment .1 cm x .1 cm x 10 cm (4 inch wire length of 17 gauge
wire)

average speed of each electron in the current = 10 cm/sec = 4 inches/
sec

volume of wire segment .1 cc = b

n = number of electrons in wire segment = bd

f = fraction of an amp flowing = n/ Q = bd/Q

f = (.1cc x 8.5 x 10 ^22 electrons / cc) / 6.2 x 10 ^ 18 electrons

8.5/6.2 x 10^3 = 1400 amps flowing at 4 inches per second, DC

or if 14 amps are flowing, the speed is 100 times slower = .04 inches
per second

 

[George Herold]

On May 8, 11:05 am, Globemaker <alanfolms...@cabanova.com> wrote:

Electrons in a wire commonly travel much more slowly than most people
expect. A simple calculation will show that in many common wires in
houses, radios, and computers, the average speed of current flow is
less than one meter per second. That slow current carries signals at
more than 20% of the speed of light in a vacuum. Details at 11...

OK, What's the rms velocity of an electron in a wire. (assume room
temperature.)

George H.

 

[Globemaker]

On May 9, 11:05 am, George Herold <gher...@teachspin.com> wrote:

On May 8, 11:05 am, Globemaker <alanfolms...@cabanova.com> wrote:

Electrons in a wire commonly travel much more slowly than most people
expect. A simple calculation will show that in many common wires in
houses, radios, and computers, the average speed of current flow is
less than one meter per second. That slow current carries signals at
more than 20% of the speed of light in a vacuum. Details at 11...

OK, What's the rms velocity of an electron in a wire.  (assume room
temperature.)

George H.
Geo. asked:

"What's the rms velocity of an electron in a wire?"

http://www.funtrivia.com/askft/Question62273.html

The rms (root mean square) thermal speed of electrons is given by
Vrms = (3kT/m)^(1/2)
where k is Boltzmann's constant, T is the temperature, and m is the
electron mass...
Vrms = 1.15 x 10^5 m/s at 20 degrees C.
or rather.... 100,000 m/s.

The speed of light in a vacuum (c) is 300,000,000 meters per second or
3000 times as fast an that electron.

The speed of a signal in a wire (transmission line) is 1/(c(sqrt(LC))
where L and C are calculated here:

http://www.rfcafe.com/references/electrical/coax.htm

C is commonly 67 pf / meter

 

[Globemaker]

correction
the speed of a signal on a wire : v= 1/sqrt(LC)
the speed of light in an insulator v = 1/sqrt(permeability times
permittivity)
see the similarity?
http://en.wikipedia.org/wiki/Permittivity

 

[Bret Cahill]

Kind of like a train changing acceleration [jerk] when the velocity is
only 5 mph. The slack in the couplings is only about an inch or so so
the clatter up or down the train moves at 400 mph.

This phenomenon is easy to quantify intellectually but is still
emotionally surprising, at least more than what might be expected.

Someone needs to make a list of this stuff.


Bret Cahill

On Sun, 8 May 2011 08:05:43 -0700 (PDT), Globemaker

alanfolms...@cabanova.com> wrote:
Electrons in a wire commonly travel much more slowly than most people
expect. A simple calculation will show that in many common wires in
houses, radios, and computers, the average speed of current flow is
less than one meter per second. That slow current carries signals at
more than 20% of the speed of light in a vacuum. Details at 11...

... and in AC circuits, the electrons just go back and forth
and never make net progress down the wire!

The teaching analogy I like best for the slow drift velocity
but high information speed is " marbles in a pipe".  I made
such a model to demonstrate to my (then) young nephew, using
a foot of 7/8 PVC pipe, filled with same-colored marbles.

Use a long rubber band from one end of the pipe to the other
to hold the marbles in place when you turn it vertical.
Prepare this ahead of time, so the subject(s) don't know
what you've done, and present it like magic trick:  You
gently push a (same-colored) marble into the bottom of the
pipe (past the rubber band) and it appears to instantly pop
out of the top!  (Shoots up in the air a bit, when it
overcomes the tension of the rubber band.)

Do this a few times, then push a different-colored marble in
the bottom.  Hmm, an original-colored marble pops out the
top.  Keep pushing in new marbles, until finally the odd one
pops out.  

Explain that this is like electricity, where one electron
going into a wire pushes all the others along so that a
different electron "instantly" pops out the other end.
Since all electrons are interchangeable, it only *seems*
that they move with great speed through the wire.

(Follow up:  Years later, my nephew is now preparing to
become an auto mechanic... so maybe this great teaching tool
didn't stick.  But at the time, he sure seemed to enjoy all
the marbles bouncing around the room!)

Best regards,

Bob Masta

              DAQARTA  v6.01
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
    Frequency Counter, FREE Signal Generator
           Pitch Track, Pitch-to-MIDI
          Science with your sound card!

 

[Rich Grise]

Bret Cahill wrote:

when the velocity is
only 5 mph. The slack in the couplings is only about an inch or so so
the clatter up or down the train moves at 400 mph.

This phenomenon is easy to quantify intellectually but is still
emotionally surprising, at least more than what might be expected.

Someone needs to make a list of this stuff.

OK, go ahead! ;-)

Cheers!
Rich

 

[Phil Hobbs]

Rich Grise wrote:

Bret Cahill wrote:

Kind of like a train changing acceleration [jerk] when the velocity is
only 5 mph. The slack in the couplings is only about an inch or so so
the clatter up or down the train moves at 400 mph.

This phenomenon is easy to quantify intellectually but is still
emotionally surprising, at least more than what might be expected.

Someone needs to make a list of this stuff.

OK, go ahead! ;-)

Cheers!
Rich

Waves are almost all like that. Normal wave behaviour requires particle
velocities much less than the wave propagation velocity. A compression
wave moving faster than the speed of sound is called a 'shock wave'.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

 

[whit3rd]

On Monday, May 9, 2011 8:14:01 AM UTC-7, Globemaker wrote:

On May 9, 11:05 am, George Herold <ghe...@teachspin.com> wrote:
On May 8, 11:05 am, Globemaker <alanfo...@cabanova.com> wrote:

Electrons in a wire commonly travel much more slowly than most people
expect....

"What's the rms velocity of an electron in a wire?"

http://www.funtrivia.com/askft/Question62273.html

The rms (root mean square) thermal speed of electrons is given by
Vrms = (3kT/m)^(1/2)
where k is Boltzmann's constant, T is the temperature, and m is the
electron mass...

Well, nearly. That's only for a free electron gas, not for the highly
constrained electrons in a wire. The valence electrons are the only
free ones (other electrons in lower shells are stuck), and they have
an 'effective mass' that includes the electron's interaction with
all the surrounding matter.

 

[Rich Grise]

Phil Hobbs wrote:

Rich Grise wrote:
Bret Cahill wrote:

Kind of like a train changing acceleration [jerk] when the velocity is
only 5 mph. The slack in the couplings is only about an inch or so so
the clatter up or down the train moves at 400 mph.

This phenomenon is easy to quantify intellectually but is still
emotionally surprising, at least more than what might be expected.

Someone needs to make a list of this stuff.

OK, go ahead! ;-)

Waves are almost all like that. Normal wave behaviour requires particle
velocities much less than the wave propagation velocity. A compression
wave moving faster than the speed of sound is called a 'shock wave'.

Even the wave in a stadium follows the same principles. The wave itself

move much faster than a person being moshed would. ;-)

Cheers!
Rich

 

[Globemaker]

On May 10, 3:16 pm, whit3rd <whit...@gmail.com> wrote:

On Monday, May 9, 2011 8:14:01 AM UTC-7, Globemaker wrote:
On May 9, 11:05 am, George Herold <ghe...@teachspin.com> wrote:
On May 8, 11:05 am, Globemaker <alanfo...@cabanova.com> wrote:

Electrons in a wire commonly travel much more slowly than most people
expect....
"What's the rms velocity of an electron in a wire?"

http://www.funtrivia.com/askft/Question62273.html

The rms (root mean square) thermal speed of electrons is given by
Vrms = (3kT/m)^(1/2)
where k is Boltzmann's constant, T is the temperature, and m is the
electron mass...

Well, nearly.  That's only for a free electron gas, not for the highly
constrained electrons in a wire.  The valence electrons are the only
free ones (other electrons in lower shells are stuck), and they have
an 'effective mass' that includes the electron's interaction with
all the surrounding matter.

I see. If all electrons are considered, not just those in the
conduction band, then the kinetic statistical model cited is too
simple.

 

[Bret Cahill]

when the velocity is
only 5 mph.  The slack in the couplings is only about an inch or so so
the clatter up or down the train moves at 400 mph.

This phenomenon is easy to quantify intellectually but is still
emotionally surprising, at least more than what might be expected.

Someone needs to make a list of this stuff.

OK, go ahead! ;-)

Cheers!
Rich

Waves are almost all like that.  Normal wave behaviour requires particle
velocities much less than the wave propagation velocity.  A compression
wave moving faster than the speed of sound is called a 'shock wave'.

Cheers

That's not something that is intuitively obvious from childhood
experiences like most Newtonian physics.

The train coupling example is somewhere in between. It can get people
to think when they ordinarily wouldn't think.


Bret Cahill

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) nethttp://electrooptical.net- Hide quoted text -

- Show quoted text -

 

[George Herold]

On May 10, 5:23 pm, Globemaker <alanfolms...@cabanova.com> wrote:

On May 10, 3:16 pm, whit3rd <whit...@gmail.com> wrote:





On Monday, May 9, 2011 8:14:01 AM UTC-7, Globemaker wrote:
On May 9, 11:05 am, George Herold <ghe...@teachspin.com> wrote:
On May 8, 11:05 am, Globemaker <alanfo...@cabanova.com> wrote:

Electrons in a wire commonly travel much more slowly than most people
expect....
"What's the rms velocity of an electron in a wire?"

http://www.funtrivia.com/askft/Question62273.html

The rms (root mean square) thermal speed of electrons is given by
Vrms = (3kT/m)^(1/2)
where k is Boltzmann's constant, T is the temperature, and m is the
electron mass...

Well, nearly.  That's only for a free electron gas, not for the highly
constrained electrons in a wire.  The valence electrons are the only
free ones (other electrons in lower shells are stuck), and they have
an 'effective mass' that includes the electron's interaction with
all the surrounding matter.

I see. If all electrons are considered, not just those in the
conduction band, then the kinetic statistical model cited is too
simple.- Hide quoted text -

- Show quoted text -

Not quite, electrons in solids are a bit different from electrons in
free space.

Do you 'do' electronics or do you just like to web search?

George H.

 

[Globemaker]

On May 10, 10:23 pm, George Herold <gher...@teachspin.com> wrote:

Not quite, electrons in solids are a bit different from electrons in
free space.

Do you 'do' electronics or do you just like to web search?

George H.

Both. Doing electronics ranges from inventing to pushing buttons.
Search engines are a tools for reviewing basic electronics or
glimpsing someone's research. This week's searches have been to learn
about OLED, organic light emitting diodes. Also, a crystal ball has
been done as a paper design. Imagine a 3D display as a sphere of glass
mixed with samarium and europium phosphors, lit by 3 colors of laser
beams. There is a problem with multiple points being illuminated that
are not wanted. More ideas are needed.

 

[Rich Grise]

Bret Cahill wrote:

when the velocity is
only 5 mph.  The slack in the couplings is only about an inch or so so
the clatter up or down the train moves at 400 mph.

This phenomenon is easy to quantify intellectually but is still
emotionally surprising, at least more than what might be expected.

Someone needs to make a list of this stuff.

OK, go ahead! ;-)

Waves are almost all like that.  Normal wave behaviour requires particle
velocities much less than the wave propagation velocity.  A compression
wave moving faster than the speed of sound is called a 'shock wave'.

That's not something that is intuitively obvious from childhood
experiences like most Newtonian physics.

The train coupling example is somewhere in between. It can get people
to think when they ordinarily wouldn't think.

A slinky can also work - you can do longitudinal or transverse waves.

Did you ever see those videos of the astronauts playing with the slinky
in orbit? That was way kewl!

Cheers!
Rich

 

[George Herold]

On May 11, 1:05 am, Globemaker <alanfolms...@cabanova.com> wrote:

On May 10, 10:23 pm, George Herold <gher...@teachspin.com> wrote:

Not quite, electrons in solids are a bit different from electrons in
free space.

Do you 'do' electronics or do you just like to web search?

George H.

Both. Doing electronics ranges from inventing to pushing buttons.
Search engines are a tools for reviewing basic electronics or
glimpsing someone's research. This week's searches have been to learn
about OLED, organic light emitting diodes. Also, a crystal ball has
been done as a paper design. Imagine a 3D display as a sphere of glass
mixed with samarium and europium phosphors, lit by 3 colors of laser
beams. There is a problem with multiple points being illuminated that
are not wanted. More ideas are needed.

OK, most of my electronics is stealing someone else's circuit and then
trying to find parts that match my application. I'm much more of a
knob turner, buttons are so digital. :^)

George H.

 

[Bret Cahill]

when the velocity is
only 5 mph.  The slack in the couplings is only about an inch or so so
the clatter up or down the train moves at 400 mph.

This phenomenon is easy to quantify intellectually but is still
emotionally surprising, at least more than what might be expected.

Someone needs to make a list of this stuff.

OK, go ahead! ;-)

Waves are almost all like that.  Normal wave behaviour requires particle
velocities much less than the wave propagation velocity.  A compression
wave moving faster than the speed of sound is called a 'shock wave'.

That's not something that is intuitively obvious from childhood
experiences like most Newtonian physics.

The train coupling example is somewhere in between.  It can get people
to think when they ordinarily wouldn't think.

A slinky can also work - you can do longitudinal or transverse waves.

Maybe some waves are easier to understand than train clatter.

Did you ever see those videos of the astronauts playing with the slinky
in orbit? That was way kewl!

I'm still trying to get them to do the Brazil nut effect.

Toss a rock through sand coming off a conveyor belt and the rock will
penetrate. Toss a rock down onto a beach and the rock won't get very
far. The "beach" lasts longer on the bottom of the can than the top
so the rock moves upwards. This is why there is a maximum effect at a
certain acceleration/displacement.


Bret Cahill