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### Author Topic: Thicker wire has less resistance, why doesn't that become a superconductor  (Read 2280 times)

#### postingsite

• Full Member
• Posts: 114
##### Thicker wire has less resistance, why doesn't that become a superconductor
« on: December 06, 2018, 12:30:43 AM »
Thicker wire has less resistance, why doesn't that become a superconductor

I repeatedly read that if you use thicker wire,  there will be less resistance .
- However, I could not find if there is a limit to that effect, or formulas etc
( you'd think this would be common stuff for electricians etc )

- Why doesn't this reach a point where it becomes a superconductor .

- Also, if you use thicker wire, does the surrounding electromagnetic-field shrink .

So what if you use a  small 1.5-volt battery watch battery,  to send a single pulse into a 1-meter diameter / thick continuous loop of copper, what will happen to that current, will it become persistent-current ?
- Also, while the current travels around the loop, will the electromagnetic-field emitted by the loop be smaller or greater than that of a loop of 1-cm diameter / thick wire .

#### ayeaye

• Hero Member
• Posts: 866
##### Re: Thicker wire has less resistance, why doesn't that become a superconductor
« Reply #1 on: December 06, 2018, 01:48:08 AM »
Superconductor is not just less resistance. Superconductor is where electrons go around obstacles in an organized way, they move together, thus in a way they never bump into obstacles.

You can make a superconductor, if you want. You only need some liquid nitrogen, which is cheap. And melting the right material together from powders. I think you need a gas welder, not sure. I'm sure though that you find instructions how to make a superconductor, if you search.

#### F6FLT

• Sr. Member
• Posts: 394
##### Re: Thicker wire has less resistance, why doesn't that become a superconductor
« Reply #2 on: December 06, 2018, 09:40:41 AM »
Thicker wire has less resistance, why doesn't that become a superconductor
...
because R→0 doesn't mean R=0.

#### Turbo

• Sr. Member
• Posts: 271
##### Re: Thicker wire has less resistance, why doesn't that become a superconductor
« Reply #3 on: December 06, 2018, 11:05:56 AM »
I was told that only the electrons in the most outer shell, the so called valence band, are most free to move around.
This is also what supposedly causes the so called skin effect.
These electrons seem to be rushing along and over the surface of the wire.
Now thicker wire means more surface area, so more space to move about.
But these electrons are still bound to the metal, unless you heat it to red hot temperatures, as happens in light bulbs and tube filaments.
In that case some electrons gain enough kinetic energy to escape the binding force, and this gives rise to the so called electron cloud that exists around the cathode.
These floating electrons are truly free electrons and that is what makes it possible to steer large electron streams with either magnetic field or electrostatic driving mechanism, like the grid.
Having a superconductor by itself would be meaningless because you would only lower the costs of transportation and they are already very low, you would still need to apply the energy to the appliance you want to power.
The little resistance that does exist currently generates a loss that is acceptable.
It's not that when you power a 100 Watt bulb, you lose 50 watts on the wires, if that was the case things would catch fire.
These cables stay relatively cool, so you can conclude that the loss is neglect able.

#### F6FLT

• Sr. Member
• Posts: 394
##### Re: Thicker wire has less resistance, why doesn't that become a superconductor
« Reply #4 on: December 07, 2018, 10:49:52 AM »
I was told that only the electrons in the most outer shell, the so called valence band, are most free to move around.
This is also what supposedly causes the so called skin effect.
No, there's no connection. You are right that the electrons in the outermost layer of atoms are those of conduction. But the skin effect is only the effect of the varying magnetic field produced by the electrons on themselves due to their own current. Since the force is radial, the electrons are moved to the periphery and only circulate near the surface of the conductor. As the region of the conductor where electrons circulate is reduced, the resistance is increased, especially at high frequencies. At only 1 MHz, the skin thickness used by electrons is only 66µm.
Quote
...
The little resistance that does exist currently generates a loss that is acceptable.
...
This is acceptable in some cases, such as powering household appliances.
But when you transfer a high power, you need a high voltage line to reduce the current. However, it would be much easier and cheaper if we had zero resistance lines, with much thinner wires, and much lower voltages. Even at home, 12v instead of 120 or 230v would be preferable because less dangerous. But for the same power, 12v needs much higher currents that our ordinary wires can't support.
Another case is the radio antenna. At high frequencies the skin effect is terrible. For example, the skin thickness at 1GHz is only 2µm, and this increases drastically the resistance!
Another case is the induction coil. While it is very easy to keep a voltage in an open capacitor, because its internal resistance is very high, it is very difficult to keep a current in a shorted coil, because its internal resistance is far too high even with thick wire, and the current dissipates quickly.
So a superconductor at room temperature is very highly desirable.