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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) =
0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#2
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![]() "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. |
#3
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"Gareth Magennis" wrote in message
... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. |
#4
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![]() "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. |
#5
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Gareth Magennis wrote in message
... "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. So it may be an effect of work hardening , relative increase in the effect of imperfections/micro fractures or some other metallurgical effect. Mackie speaker voice coil failures due to this flattening/ribboning process to make the tails to the outside world. Previous failure at the juncture of round to flat (0.07mm round to about 0.02 x 0.2mm) so at the peak stress point. This one along the length of the ribbon section, but the whole 50mm or so run was brittleised and disintegrated on touch, not the slightest sign of overheating on the remaining 25 turns of round wire. broken end marked B on this pic http://home.graffiti.net/diverse:gra...ckie_horn1.jpg http://home.graffiti.net/diverse:gra...ckie_horn2.jpg Cannot expore the metallurgy as that curve of "wire" as totally disintegrated to dust. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#6
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"Gareth Magennis" wrote in message
... "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. The shape of the cross section can change to virtually any dimension so long as the length remains the same. IOW, if you squeeze a bar of 10mmx10mm down to 2mmx50mm, its cross sectional area stayed constant (only the shape of the area changed). Its length will remain the same, since the volume didn't change; hence, its resistance will remain the same. So long as material is not added or removed, the volume will remain the same. The formula says that the ratio of length to cross-sectional area must remain the same in order for resistance to remain unchanged. If cross sectional area is changed, the length must change to maintain the ratio. The volume must remain constant. -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes. |
#7
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On Dec 12, 11:55*am, "DaveM" wrote:
"Gareth Magennis" wrote in message ... "DaveM" wrote in message ... "Gareth Magennis" wrote in message ... "N_Cook" wrote in message ... For a given length of fine copper wire of diameter 0.072 mm (2.9 mil) = 0.004 sq mm, if it is squashed to cross-section dimensions of 0.02 * 0.2 mm (2 * 20 mil) proportionally how much does the resistance change ? and then to 0.01 * 0.4mm (1 * 40 mil) ? AFAIK the resistance of wire is proportional to its Cross Sectional Area. Period. *If this remains unchanged, so does the resistance. Gareth. That is correct, but the length also has to remain unchanged *The formula for the resistance of a conductor is R=r*L/A where R= Resistance r=Resistivity of the conductor (1.7x10^-8 for copper) L=Length A=cross section area As you can see, the resistance remains constant as long as L and A remain the same, or change in a manner that produces the same ratio. -- So that begs the question, how much can a piece of copper wire be compressed? If you do squash it into a different shape, does or can its volume change significantly? Gareth. The shape of the cross section can change to virtually any dimension so long as the length remains the same. *IOW, if you squeeze a bar of 10mmx10mm down to 2mmx50mm, its cross sectional area stayed constant (only the shape of the area changed). *Its length will remain the same, since the volume didn't change; hence, its resistance will remain the same. So long as material is not added or removed, the volume will remain the same. The formula says that the ratio of length to cross-sectional area must remain the same in order for resistance to remain unchanged. *If cross sectional area is changed, the length must change to maintain the ratio. *The volume must remain constant. -- Dave M MasonDG44 at comcast dot net *(Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes.- Hide quoted text - - Show quoted text - What I believe Norm is questioning/proposing is that the wire may have been made more "dense" by being compressed without lengthening, and that would probably decrease its resistance. Bob Hofmann |
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