Speed of light question

If I have a 100 foot long wire that has no slack where movement of the wire turns on a light at the other end and I also can send an electric charge through the wire that will also turn on a light at the other end. Which light would turn on first if I move the wire and also initiate the electrical charge at the same moment.

In other words would the electrical charge be faster than the motion on the wire? Also consider if you used a light photon initiated toward the other end to turn on a light? Would the light or motion win the race?

do your own homework.

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reply to post by randomname


Not taking any classes. Just watching Universe on H2 and the thought came to me and I would enjoy a disccusion about it.

reply to post by Xeven


Explanation: S&F!

The electricity in the wire travels at 2/3rds [aprox] the speed of light due to the natural resistance of the wire.

The photon would move at the speed of light in a fluid medium [ in this case air] and thats slower than speed of light in a vacuum. By how much I have no immediate clue?

The wire itself, in an atmosphere, would have to travel at faster than 2/3rds the speed of light to beat the electrical charge.

Personal Disclosure: I think the photon would win especially if the test was conducted in a vacuum.

reply to post by Xeven


Both the light and the electric charge will reach the other end before the rope is able to turn on the light. Regardless of how tight the rope is, it is still elastic, especially at the molecular level. The transfer of the pull through the molecules in the rope will always be slower.

With just a 100-ft rope, though, the difference would be negligible. With a rope millions of kilometers long, the light will begin to very obviously reach the other end before the pull is able to "travel" from one end to the other.

delete post

If this isn't a test question, you should definitely get paid to write them.
That's all.

Ok think about the same scenario again but this time instead of a wire think off a tube full of water. If you squirted water in at on end then the movement of the water at the other end turns on the light. Water doesn't compress like a wire can stretch.

So could the movement of the water be faster than the speed of electricity down a wire?

reply to post by Xeven


Both the light and the electrical charge would beat the motion activation. With only 100ft, all of the differences would be negligible.

reply to post by PhoenixOD


Water does compress, just not very much.

It will depend on where on the wire that you send the power surge through? If you put a light at each end of the wire and you send a power surge at the middle of the wire? Both lights at each end should turn on at the same time. Then again. If you put one light in the middle of the wire and the other at the end of the wire and send a power surge at end of the wire? The light in the middle should turn on before the light at the end turns on. The light closes to where you send the power surge through, will always be the one to turn on first.

Originally posted by Xeven
If I have a 100 foot long wire that has no slack where movement of the wire turns on a light at the other end and I also can send an electric charge through the wire that will also turn on a light at the other end. Which light would turn on first if I move the wire and also initiate the electrical charge at the same moment.

In other words would the electrical charge be faster than the motion on the wire? Also consider if you used a light photon initiated toward the other end to turn on a light? Would the light or motion win the race?

Moving the wire around will not change the speed of the electric charge. The lights will always turn on the same time no matter where you've send the photon through. It will be the photon that will turn on the light first. A matter of fact, you can receive a voice message faster by using photon, then by using the convenient way.

IMO I honestly think the movement of the wire (non compressable/stretchable) would trigger the light first by movement and then by electric wire. Given that the switch and push/pull are done at point A and transmitted to the 2 lights at point B and all switches trigger when a micron of movment is detected. The rod is already at point B, the electron is still at point A.

reply to post by XL5


Regardless of our non-stretchable the wire is, it will still take more time for the movement to transfer through the wire than for the electric charge/light to travel through it. The pull has to be transferred through molecular forces...this will always be slower.

reply to post by XL5


Explanation: The fastest a pressure wave can pass through an object is the speed of sound in that object!

For example in diamond wire it would be ... Velocity of sound in some common solids [engineeringtoolbox.com]

Diamond:- 12000m/s or 39400ft/s

Speed of Sound: Long Rods [wiki]

Long rods:
The speed of sound for longitudinal waves in stiff materials such as metals is sometimes given for "long, thin rods" of the material in question, in which the speed is easier to measure. In rods where their diameter is shorter than a wavelength, the speed of pure longitudinal waves may be simplified and is given by:

This is similar to the expression for shear waves, save that Young's modulus replaces the shear modulus. This speed of sound for longitudinal waves in long, thin rods will always be slightly less than the 3-D, longitudinal wave speed in an isotropic materials, and the ratio of the speeds in the two different types of objects depends on Poisson's ratio for the material.

Personal Disclosure: Even using a diamond wire with 12km/sec impetus is some 29,988km [aprox] too slow compared with a photon in a vacuum.

Wow thank you for all the answers. I think I can actually imagine why motion would be slower though at first I really thought the oposite would be true.

Now... if I entangle two atoms.... light or entanglement?

reply to post by Xeven


Entanglement, hands down...provided you can get the entangled atom at the other end to turn the light on.

Originally posted by CLPrime
reply to post by Xeven

 

Entanglement, hands down...provided you can get the entangled atom at the other end to turn the light on.

Does that mean the speed of light is not the fastest thing in the universe once you get down to the quantum level?

reply to post by Xeven


motion is instantaneous, motion would win

reply to post by Xeven


That's right...quantum physics requires that entanglement be instantaneous. The catch is, entanglement can't be used to transmit information instantaneously. This was the caveat of Special Relativity...that information cannot be transmitted faster than the speed of light. Action is free to happen instantaneously as long as it doesn't transmit information.