Monday, May 30, 2011
Monday, May 23, 2011
OHM'S LAW
Nowadays high school and university students use voltmeters and ammeters to demonstrate Ohm's law. These devices were not available in Ohm's time! (Moreover, these devices rely on laws (including Ohm's law) not known at the time.) How did Ohm do it? Suggest experiments (using only equipment available in 1826, or similar present-day equipment) showing that:
(a) "voltage" is proportional to "current";
(b) for fixed "voltage", the "current" is proportional to the cross-sectional area of the wire and inversely proportional to its length.
The solution:
As a voltage source we can use batteries. Ohm first used "chemical batteries" but those had very short life-time, i.e their electromotive force (EMF) varied during the experiment. Eventually, he used a thermocouple as a voltage source. The voltage, or more correctly the EMF, was therefore N*E where N is the number of batteries connected in series and E is EMF of a single battery. If the resistance of wire was X, and internal resistance of the battery was r, then the current I was given by
I=N*E/(N*r+X)
Current can be measured by placing a magnetized needle hanging on a string at certain fixed distance from the wire. Since we are not supposed to know exactly the angular dependence of the magnetic force, we will simply for each current twist the string on which the needle hangs until the needle returns in its position before the current began flowing. The angle by which the string was twisted is proportional to the force momentum, and thus measures the strength of the current. (Of course we assume that forces are indeed proportional to the current.)
We will begin the experiment by keeping the same wire (the same X) and changing N. By plotting 1/I versus 1/N, we will establish r/E, and will establish the "voltage-current" relation of the Ohm's law. Now, by lengthening the wire of making its cross section larger we can investigate dependence of resistance on geometry of the wire. (Of course we cannot measure the actual absolute values of the resistance, but all we need is the dependence on length and cross section area...) Ohm published his results on geometry dependence of X in Journal fur Chemie und Physik, 46, p. 160 (1826).
Nice short description of Ohm's work in its historic context can be found in the book History of Physics (Storia della Fisica) by Mario Gliozzi.
Comment: Groshaus suggested to measure the voltage by attaching one of the leads of the battery to electroscope. Can it be done with sufficient accuracy?
(a) "voltage" is proportional to "current";
(b) for fixed "voltage", the "current" is proportional to the cross-sectional area of the wire and inversely proportional to its length.
The solution:
As a voltage source we can use batteries. Ohm first used "chemical batteries" but those had very short life-time, i.e their electromotive force (EMF) varied during the experiment. Eventually, he used a thermocouple as a voltage source. The voltage, or more correctly the EMF, was therefore N*E where N is the number of batteries connected in series and E is EMF of a single battery. If the resistance of wire was X, and internal resistance of the battery was r, then the current I was given by
I=N*E/(N*r+X)
Current can be measured by placing a magnetized needle hanging on a string at certain fixed distance from the wire. Since we are not supposed to know exactly the angular dependence of the magnetic force, we will simply for each current twist the string on which the needle hangs until the needle returns in its position before the current began flowing. The angle by which the string was twisted is proportional to the force momentum, and thus measures the strength of the current. (Of course we assume that forces are indeed proportional to the current.)
We will begin the experiment by keeping the same wire (the same X) and changing N. By plotting 1/I versus 1/N, we will establish r/E, and will establish the "voltage-current" relation of the Ohm's law. Now, by lengthening the wire of making its cross section larger we can investigate dependence of resistance on geometry of the wire. (Of course we cannot measure the actual absolute values of the resistance, but all we need is the dependence on length and cross section area...) Ohm published his results on geometry dependence of X in Journal fur Chemie und Physik, 46, p. 160 (1826).
Nice short description of Ohm's work in its historic context can be found in the book History of Physics (Storia della Fisica) by Mario Gliozzi.
Comment: Groshaus suggested to measure the voltage by attaching one of the leads of the battery to electroscope. Can it be done with sufficient accuracy?
Sunday, May 22, 2011
JOPLIN MISSOURI Tornado Updates/Info
I'm posting info that I am receiving from a friend in Joplin Mo via Twitter. I will try and post info here also.
Please DO NOT SELF DEPLOY to Joplin.
The area is using their emergency response plan that is in place & it is working.
They cannot manage spontaneous volunteers at this time.
Please call 2-1-1 (800.427.4626) to let them know if you are interested in volunteering and they will provide a coordinated effort to manage volunteers.
--------------------------------
National Americorp Volunteers are setting up a national hotline for residents to call to check on loved ones.
The number is (417) 659-5464.
It will be active later this morning.
Update on Joplin School District -
more than 5-thousand displaced;
searching for staff and students
Click Here
http://fourstateshomepage.com/fulltext/?nxd_id=192157
NEW UPDATE:2:20 am
Missouri Media Sites
Joplin - KODE
Channel 12 - ABC
Joplin - KSN
Channel 16 - NBC
Springfield - KSPR
Channel 33 - ABC
Springfield - KYTV
Channel 3 - NBC
KKLL AM Joplin,
KWAS AM Joplin,
Joplin Globe
Springfield News Leader
My Twitter; KD8BIG
*Joplin, Missouri hit hard by tornado, Officials are asking for help, SAR Teams, Doctors, nurses, paramedics etc.
*Jasper Co requesting Mutual Aid for Officers...PD set up @ 20th and Main
*24 deaths in wake of tornado in Joplin, MO, http://bit.ly/jaJ5iR
*Real-time updates, images from tornado-damaged Joplin, via breakingnews.com http://bit.ly/iP1nNF
*Tornado Watches continue into Monday (4 am CDT) for parts of MO, AR, OK, IL http://1.usa.gov/joqgtB | http://1.usa.gov/ax7VwV
*Blankets and medical supplies needed at destroyed nursing home St 26th & Jackson in Joplin, Mo
*For nurses or doctors looking to help re Joplin, MO, call 417-832-9500 for the Greater Ozarks of the Red Cross.
Please DO NOT SELF DEPLOY to Joplin.
The area is using their emergency response plan that is in place & it is working.
They cannot manage spontaneous volunteers at this time.
Please call 2-1-1 (800.427.4626) to let them know if you are interested in volunteering and they will provide a coordinated effort to manage volunteers.
--------------------------------
National Americorp Volunteers are setting up a national hotline for residents to call to check on loved ones.
The number is (417) 659-5464.
It will be active later this morning.
Update on Joplin School District -
more than 5-thousand displaced;
searching for staff and students
Click Here
http://fourstateshomepage.com/fulltext/?nxd_id=192157
NEW UPDATE:2:20 am
Missouri Media Sites
Joplin - KODE
Channel 12 - ABC
Joplin - KSN
Channel 16 - NBC
Springfield - KSPR
Channel 33 - ABC
Springfield - KYTV
Channel 3 - NBC
KKLL AM Joplin,
KWAS AM Joplin,
Joplin Globe
Springfield News Leader
My Twitter; KD8BIG
*Joplin, Missouri hit hard by tornado, Officials are asking for help, SAR Teams, Doctors, nurses, paramedics etc.
*Jasper Co requesting Mutual Aid for Officers...PD set up @ 20th and Main
*24 deaths in wake of tornado in Joplin, MO, http://bit.ly/jaJ5iR
*Real-time updates, images from tornado-damaged Joplin, via breakingnews.com http://bit.ly/iP1nNF
*Tornado Watches continue into Monday (4 am CDT) for parts of MO, AR, OK, IL http://1.usa.gov/joqgtB | http://1.usa.gov/ax7VwV
*Blankets and medical supplies needed at destroyed nursing home St 26th & Jackson in Joplin, Mo
*For nurses or doctors looking to help re Joplin, MO, call 417-832-9500 for the Greater Ozarks of the Red Cross.
Friday, May 20, 2011
A Radio Shack DIY Comeback?
Radio Shack seems to be concerned with the direction of its lack of business.
I see they have a link asking for DIY individuals to explain what they would like to see Radio Shack improve on.
I read through the post that many have left and there are some Amateur Radio Operators (HAMS) that have left their own personal feelings.
For me, a hobbyist in many areas, I loved Radio Shack when I was a kid. That was the place for me when I was 6-18 years of age.
It seems to me that Radio Shack had lost there way in the early to mid 80s.
I have heard from many amateur radio operators that tell me how back in the day they use to spend an hour in Radio Shack, go home and build all kinds of gear.
I have not been in a Radio Shack since 1990, they did not have a thing I needed, I ended up at an appliance store to get my electronic supplies, go figure~
For me to make my grand appearance in a Radio Shack store they need to have stocked shelves with everything I need to make a transceiver, antenna or linear amplifier. That’s just for starters; I also have many other hobbies that require the use of an electronic store such as cell phones, computers, scanners, remote control cars/trucks/ planes, Train-Sets etc.
Let’s put it this way, Radio Shack use to be a store for the geek and the hobbyist.
I do not understand why they would not consider a dealer contract to sell with the following Amateur Radio Gear and Equipment:
ALINCO
ASTRON
Butternut Antennas
COMET Antennas
CUSHCRAFT
DIAMOND Antenna
Farallon Electronics
GAP
Grundig
HEiL
HUSTLER
Hy-gain
ICOM
Kantronics
KENWOOD
LARSEN Antennas
LDG
Maldol
MFJ
OUTbacker
Palstar
Tigertronics
Timewave Technology
VIBROPLEX
West Mountain Radio
WOUXUM
YAESU
This is the short list. I have a huge list at the bottom of my blog.
I hope someone from Radio Shack sees this and takes it to heart.
I have spent almost 2 grand on e-bay for shipping and rather spend it at my local electronics store.
73.
Tell Radio Shack how you feel~
Click Here
I see they have a link asking for DIY individuals to explain what they would like to see Radio Shack improve on.
I read through the post that many have left and there are some Amateur Radio Operators (HAMS) that have left their own personal feelings.
For me, a hobbyist in many areas, I loved Radio Shack when I was a kid. That was the place for me when I was 6-18 years of age.
It seems to me that Radio Shack had lost there way in the early to mid 80s.
I have heard from many amateur radio operators that tell me how back in the day they use to spend an hour in Radio Shack, go home and build all kinds of gear.
I have not been in a Radio Shack since 1990, they did not have a thing I needed, I ended up at an appliance store to get my electronic supplies, go figure~
For me to make my grand appearance in a Radio Shack store they need to have stocked shelves with everything I need to make a transceiver, antenna or linear amplifier. That’s just for starters; I also have many other hobbies that require the use of an electronic store such as cell phones, computers, scanners, remote control cars/trucks/ planes, Train-Sets etc.
Let’s put it this way, Radio Shack use to be a store for the geek and the hobbyist.
I do not understand why they would not consider a dealer contract to sell with the following Amateur Radio Gear and Equipment:
ALINCO
ASTRON
Butternut Antennas
COMET Antennas
CUSHCRAFT
DIAMOND Antenna
Farallon Electronics
GAP
Grundig
HEiL
HUSTLER
Hy-gain
ICOM
Kantronics
KENWOOD
LARSEN Antennas
LDG
Maldol
MFJ
OUTbacker
Palstar
Tigertronics
Timewave Technology
VIBROPLEX
West Mountain Radio
WOUXUM
YAESU
This is the short list. I have a huge list at the bottom of my blog.
I hope someone from Radio Shack sees this and takes it to heart.
I have spent almost 2 grand on e-bay for shipping and rather spend it at my local electronics store.
73.
Tell Radio Shack how you feel~
Click Here
Thursday, May 19, 2011
BREAKING NEWS--70cm is SAFE
May 19, 2011, Massapequa Park, NY - A delegation of Amateur Radio operators from the Long Island / New York City area met this morning with Congressman Peter T. King (R-NY) to discuss his recent proposed legislation, HR 607, and its impact on Amateur Radio.
Congressman King said that he fully understands and appreciates the importance
of Amateur Radio and the service it provides to the community, and that he would see to the modification of the bill so that the 420 - 440 MHz band would be
excluded from the spectrum to be auctioned. The delegation included Mike
Lisenco, N2YBB, ARRL Section Manager for New York City / Long Island (NLI),
Peter Portanova, WB2OQQ, NLI Local Government Liaison (LGL), George Tranos,
N2GA, NLI State Government Liaison (SGL), and Jim Mezey, W2KFV, NLI ARES Section Emergency Coordinator (SEC).
"The Congressman went on to explain that it was never his intention to remove
the 70 centimeter band from Amateur use. He further asked us to `get the word
out' and inform the Amateur Radio community that 70 centimeters is not in
jeopardy," said Lisenco.
Lisenco, Mezey and Tranos spoke about the importance of Amateur Radio emergency communications while Portanova, who is also the local AMSAT representative, addressed satellite and other amateur use of the 70 centimeter band.
The Congressman was very receptive to the group, who also extended an invitation to attend Field Day locations in his District.
source
Congressman King said that he fully understands and appreciates the importance
of Amateur Radio and the service it provides to the community, and that he would see to the modification of the bill so that the 420 - 440 MHz band would be
excluded from the spectrum to be auctioned. The delegation included Mike
Lisenco, N2YBB, ARRL Section Manager for New York City / Long Island (NLI),
Peter Portanova, WB2OQQ, NLI Local Government Liaison (LGL), George Tranos,
N2GA, NLI State Government Liaison (SGL), and Jim Mezey, W2KFV, NLI ARES Section Emergency Coordinator (SEC).
"The Congressman went on to explain that it was never his intention to remove
the 70 centimeter band from Amateur use. He further asked us to `get the word
out' and inform the Amateur Radio community that 70 centimeters is not in
jeopardy," said Lisenco.
Lisenco, Mezey and Tranos spoke about the importance of Amateur Radio emergency communications while Portanova, who is also the local AMSAT representative, addressed satellite and other amateur use of the 70 centimeter band.
The Congressman was very receptive to the group, who also extended an invitation to attend Field Day locations in his District.
source
SCATTERING DIPOLES
A system consists of two ideal dipoles placed at positions (0,0,0) and (0,0,a). Dipole moment p of each dipole is related to electric field E on that dipole via relation p=gE. (g is so small that you can neglect the interaction between the dipoles, i.e. electric field created by one dipole at the position of the other dipole is negligible.) An incoming electromagnetic wave of wavelength L=2a is scattered by the system. Consider two cases: (a) the incoming wave is in x-direction, and (b) the incoming wave is in z-direction. Estimate the ratio between the total scattering cross sections between those two cases. (You may neglect dimensionless prefactors of order unity.)
Solution:
(Comment: All expressions are presented in Gaussian electromagnetic units.)
When electromagnetic field propagates x direction, both dipoles will will feel the same field at the same time, and the total electric dipole of the system will be p=2gE. Since the dipoles are not close to each other, the system will also have higher moments (e.g. quadrupole), and its radiation will not be pure dipole radiation. However, the order of magnitude estimate of dipole radiation will suffice in an estimate of the cross section. We note the the power radiated by a dipole must be proportional to p2, since the electric field must be proportional to charge (and thus to dipole moment), and the power is proportional to squared field. From dimensional considerations, the radiated power must be of order cp2/L4, where c is the speed of light. Substituting, expression for p, and dividing the result by the flux of the incoming wave, we find that the cross section is of order g2/L4. (This expression could be obtained directly from dimensional analysis.)
When electromagnetic field propagates z direction, both dipoles will feel field pointing in opposite directions, and consequently the total dipole moment will vanish. However, one can easily convince himself, that non-vanishing elements of quadrupole moment are of order Q=pa=gaE. From dimensional considerations, we can also establish that the radiation of quadrupole is of order cQ2/L6. Substituting, expression for Q, and dividing the result by the flux of the incoming wave, we find that the cross section is of order g2a2/L6. Since L=2a, this expression is of the same order as cross section obtained in the i previous ("dipole radiation").
Those results really should not be surprising: Once we established that cross section must be proportional to squared charges (and thus to g2, and keeping in mind that the units of g are [length]3, we must divide g2 by something with dimensions [length]4 to obtain a cross section (that has units [length]2). Since a and L are of the same order, we can use one of them to get the correct result g2/L4.
Solution:
(Comment: All expressions are presented in Gaussian electromagnetic units.)
When electromagnetic field propagates x direction, both dipoles will will feel the same field at the same time, and the total electric dipole of the system will be p=2gE. Since the dipoles are not close to each other, the system will also have higher moments (e.g. quadrupole), and its radiation will not be pure dipole radiation. However, the order of magnitude estimate of dipole radiation will suffice in an estimate of the cross section. We note the the power radiated by a dipole must be proportional to p2, since the electric field must be proportional to charge (and thus to dipole moment), and the power is proportional to squared field. From dimensional considerations, the radiated power must be of order cp2/L4, where c is the speed of light. Substituting, expression for p, and dividing the result by the flux of the incoming wave, we find that the cross section is of order g2/L4. (This expression could be obtained directly from dimensional analysis.)
When electromagnetic field propagates z direction, both dipoles will feel field pointing in opposite directions, and consequently the total dipole moment will vanish. However, one can easily convince himself, that non-vanishing elements of quadrupole moment are of order Q=pa=gaE. From dimensional considerations, we can also establish that the radiation of quadrupole is of order cQ2/L6. Substituting, expression for Q, and dividing the result by the flux of the incoming wave, we find that the cross section is of order g2a2/L6. Since L=2a, this expression is of the same order as cross section obtained in the i previous ("dipole radiation").
Those results really should not be surprising: Once we established that cross section must be proportional to squared charges (and thus to g2, and keeping in mind that the units of g are [length]3, we must divide g2 by something with dimensions [length]4 to obtain a cross section (that has units [length]2). Since a and L are of the same order, we can use one of them to get the correct result g2/L4.
Wednesday, May 18, 2011
5/18/2011
I had a pretty good day today. My friend just bought a Fleetwood Expedition, what a nice bus. He got it without the sound system and televisions. No idea as to why, so today I helped him install new televisions and a home theater system. Tomorrow or this weekend we will install a satellite dish and a CB Radio. I tried talking him into getting his amateur radio license. I think I need to do some more talking.
I have done some work on my Stamp Collection and my Match Book Collection. I am thinking of selling the Match Book Collection. It is not very big, about 2000 matchbooks in all. Most are from the 40s-70s, some new ones also. I’m still thinking of what to do.
This morning I fired up the HF station for a while, I was unable to break the pileups I could find, this evening I check-in on the local 2 meter net.
Till next time. 73.
I have done some work on my Stamp Collection and my Match Book Collection. I am thinking of selling the Match Book Collection. It is not very big, about 2000 matchbooks in all. Most are from the 40s-70s, some new ones also. I’m still thinking of what to do.
This morning I fired up the HF station for a while, I was unable to break the pileups I could find, this evening I check-in on the local 2 meter net.
Till next time. 73.
Tuesday, May 17, 2011
SP9299.wav ; What's the Song? I found it.
So, I listen to online radio stations because there is nothing in Muskegon that I care for.
While listening to Z Rock, KRQR, they have often played a song and I have tried to find out the band that sings the song.
I have e-mailed the station, called the station and even filled out a "Who Sings that Song" request.
Well, after some researching of my own I found the group and song.
The only thing Z Rock would show on there web site is SP9299.wav 2010-10-14 09:34:38
The band, Skillet, the song is Awake and Alive.
While listening to Z Rock, KRQR, they have often played a song and I have tried to find out the band that sings the song.
I have e-mailed the station, called the station and even filled out a "Who Sings that Song" request.
Well, after some researching of my own I found the group and song.
The only thing Z Rock would show on there web site is SP9299.wav 2010-10-14 09:34:38
The band, Skillet, the song is Awake and Alive.
Monday, May 16, 2011
KD8BIG Collectable Hobbies
Over the last few weeks I spent some time working on my Collections;
Postage Stamps
Post Cards
Sports Cards and Memorabilia
Shot Glasses
Decanters
Bar-ware
Coins
Match Books
Avon Cologne Bottles
Knives and Swords
Bibles (Old Bibles~1900 and older)
Military Service Pins and Patches
Cookbooks and Coffee Cups
I have so many collectable hobbies.
If you wish to do some trading, selling or buying let me know.
Postage Stamps
Post Cards
Sports Cards and Memorabilia
Shot Glasses
Decanters
Bar-ware
Coins
Match Books
Avon Cologne Bottles
Knives and Swords
Bibles (Old Bibles~1900 and older)
Military Service Pins and Patches
Cookbooks and Coffee Cups
I have so many collectable hobbies.
If you wish to do some trading, selling or buying let me know.
Wednesday, May 11, 2011
KD8BIG; Articles of Interest
Whew, It has been a rough few weeks. Sorry to those of you who regularly stop to visit and seen nothing new. I am hoping to get back into the swing of things, although I do not think things will get much better over the next couple of months, just a hunch.
Articles of Interest;
Amateur radio operators still send strong signals
Before there was email, texting and Web chats, there was ham radio. And even though it might seem like a lost or dying art,
2011 Young Ham of The Year Award:
If you know a young radio amateur age 18 or younger who has done something very special in the Amateur Radio hobby
S'ville students, orbiting astronaut hold seven-minute ham radio
JOHN LUKE | The Times Students at St. Michael School in Schererville line up in the gym in preparation for an amateur radio connection with the ...
Amateur Radio Operators Are Key to Half Marathon
Aug 23, 1928 Some Doubt Expressed To Authenticity .Amateur Radio Operator Has ...
Dec 15, 1961 Oscar's Picked Up .By Eugene Ham's Radio
Articles of Interest;
Amateur radio operators still send strong signals
Before there was email, texting and Web chats, there was ham radio. And even though it might seem like a lost or dying art,
2011 Young Ham of The Year Award:
If you know a young radio amateur age 18 or younger who has done something very special in the Amateur Radio hobby
S'ville students, orbiting astronaut hold seven-minute ham radio
JOHN LUKE | The Times Students at St. Michael School in Schererville line up in the gym in preparation for an amateur radio connection with the ...
Amateur Radio Operators Are Key to Half Marathon
Aug 23, 1928 Some Doubt Expressed To Authenticity .Amateur Radio Operator Has ...
Dec 15, 1961 Oscar's Picked Up .By Eugene Ham's Radio
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