Originally posted by RamnedWell, here in The Netherlands birds sit on dummy-wires, not the high-voltage wires themselves.
Direct Current Circuits
[b]18. Why is it possible for a bird to sit on a high voltage wire without being electrocuted?[/b]
Secondly, birds don't touch the ground so the current only goes back in the wire.
Thirdly, the resistance of a bird is much higher than the resistance of a wire. Thus no electricity flows through the burd.
Originally posted by kbaumenThat's the important thing. The potential difference is too negligible for electrocution to occur. Lucky birds. How entertaining would it be to go outside at night and see huge blue sparks of electrocution hitting a gigantic flock of birds 😉
. And it also has something to do with a small potential difference.
Next question to follow.
Magnetism
19. Two wires carry currents in opposite directions and are oriented parallel, with one above the other. The wires repel each other. Is the upper wire in a stable levitation over the lower wire? Suppose the currenty in one wire is reversed, so that the wires now attract. Is the lower wire hanging in a stable attraction to the upper wire?
Expect follow-up questions.
Originally posted by RamnedIn both cases, there are two important forces acting on the wire in question: (a) the repelling/attracting force from the other wire; and (b) gravity.
Magnetism
[b]19. Two wires carry currents in opposite directions and are oriented parallel, with one above the other. The wires repel each other. Is the upper wire in a stable levitation over the lower wire? Suppose the currenty in one wire is reversed, so that the wires now attract. Is the lower wire hanging in a stable attraction to the upper wire?
Expect follow-up questions.[/b]
Case 1: The wires repel each other
In this case, the repelling force keeps the one wire hovering perfectly balanced above the other. However, any lateral perturbation to the system will cause the top wire move out of line with the bottom wire. In that case, the couple created by the repelling force (up) and gravity (down) will cause the wire to rotate away from its equilibrium position. Since the only equilibrium position for this system is with the one wire perfectly balanced above the other, this configuration is not stable.
Case 2: The wires attract each other
Now we have the one wire hovering perfectly balanced under the other wire. Any lateral perturbation to this system will result in the bottom wire moving out of line with the top wire, creating a couple consisting of the attracting force (up) and gravity (down). This couple will push the wire back into its stable equilibrium position (hanging right underneath the other wire), so this configuration is stable.
Originally posted by PBE6How does the force of attraction vary with the distance between the two wires?
[b]Case 2: The wires attract each other
Now we have the one wire hovering perfectly balanced under the other wire. Any lateral perturbation to this system will result in the bottom wire moving out of line with the top wire, creating a couple consisting of the attracting force (up) and gravity (down). This couple will push the wire back into its stabl ...[text shortened]... equilibrium position (hanging right underneath the other wire), so this configuration is stable.[/b]
I'm not sure myself, though I suspect it must decrease with distance. If this is the case, then wouldn't that make the configuration unstable to vertical perturbations? Move the lower wire down slightly, and the magnetic force would decrease, so it would keep falling.
By the same argument, the first configuration would be stable w.r.t. vertical perturbations, though I think you'd probably be right about lateral ones.
Originally posted by mtthwGood point. If the wires are only allowed to move up and down, the repelling configuration would be stable (get too low, bounces back up until gravity pulls it down again), and the attracting configuration would be unstable (too low and the wire falls, too high and the wires stick together).
How does the force of attraction vary with the distance between the two wires?
I'm not sure myself, though I suspect it must decrease with distance. If this is the case, then wouldn't that make the configuration unstable to vertical perturbations? Move the lower wire down slightly, and the magnetic force would decrease, so it would keep fall ...[text shortened]... ble w.r.t. vertical perturbations, though I think you'd probably be right about lateral ones.
Current flowing through a wire creates magnitism. Is this magnitism a constant force (at least on the macroscopic level). Could any variations in the force mess up the system? Also, magnitism is often illistrated as moving but I forget why. Would this movement somehow push the top wire sideways in the repulsion case? Just some thoughts about some other things that could be going on here.
Originally posted by PBE6No, that is wrong.
In both cases, there are two important forces acting on the wire in question: (a) the repelling/attracting force from the other wire; and (b) gravity.
[b]Case 1: The wires repel each other
In this case, the repelling force keeps the one wire hovering perfectly balanced above the other. However, any lateral perturbation to the system will cause the to ...[text shortened]... equilibrium position (hanging right underneath the other wire), so this configuration is stable.[/b]
1 edit
Originally posted by mtthwGood correction - correct.
How does the force of attraction vary with the distance between the two wires?
I'm not sure myself, though I suspect it must decrease with distance. If this is the case, then wouldn't that make the configuration unstable to vertical perturbations? Move the lower wire down slightly, and the magnetic force would decrease, so it would keep fall ...[text shortened]... ble w.r.t. vertical perturbations, though I think you'd probably be right about lateral ones.
If it is displaced upward on case 1, what happens to the repulsive force and the wire?
In case 2, what happens to the force and the wire if it is displaced downwards?
Originally posted by PBE6Lateral meaning sideways?
In both cases, there are two important forces acting on the wire in question: (a) the repelling/attracting force from the other wire; and (b) gravity.
[b]Case 1: The wires repel each other
In this case, the repelling force keeps the one wire hovering perfectly balanced above the other. However, any lateral perturbation to the system will cause the to ...[text shortened]... equilibrium position (hanging right underneath the other wire), so this configuration is stable.[/b]
In that case; how is the attracting situation stable under lateral movements?
Moving horizontally increases the distance between the wires, hence the attarctive force would decrease and the bottom wire would fall.
Originally posted by RamnedNo, the upper wire is in an unstable equilibrium. It could fall to either side easily.
Magnetism
[b]19. Two wires carry currents in opposite directions and are oriented parallel, with one above the other. The wires repel each other. Is the upper wire in a stable levitation over the lower wire? Suppose the currenty in one wire is reversed, so that the wires now attract. Is the lower wire hanging in a stable attraction to the upper wire?
Expect follow-up questions.[/b]
If the wires attract, the lower wire could conceivably be levitated stably.