Puzzle. Electrical VS solid bar switch.

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Discussion Overview

The discussion revolves around a thought experiment involving the propagation of signals in a circuit using a long bar to press a switch. Participants explore the implications of signal transmission speed in relation to electrical circuits, particularly focusing on the differences between electrical signals and mechanical pressure propagation.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant presents a scenario where a long bar is used to press a switch from a distance of 1,860,000 miles, questioning if this would result in an instantaneous light activation, suggesting a paradox with the speed of light.
  • Another participant counters that the pressure wave through the bar would propagate at the speed of sound, not instantaneously or faster than light.
  • Questions arise regarding the physical setup of the bar and whether two bars would be necessary for the current to return, indicating a need for clarification on the mechanics involved.
  • A participant speculates on the time it would take for movement at one end of a long bar to affect the other end, suggesting a significant delay based on the length of the bar.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of the scenario, particularly regarding the speed of pressure propagation versus the speed of electrical signals. No consensus is reached on the implications of the thought experiment.

Contextual Notes

Participants acknowledge the theoretical nature of the scenario, including assumptions about the absence of resistance and the physical properties of the materials involved. The discussion remains speculative without definitive conclusions.

4472
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Good Evening,

I am not a science "professional" nor even a Physics Graduate. I am, however, interested in anything with a science twist. I have created an account on this forum hoping that someone can answer my puzzing question...

Start with the simplest circuit. Battery, switch, two wires and a bulb.
Switch on and the lamp lights.
For this puzzle, assume NO resistance in the wire and a bulb (LED or whatever) that has no resistance (so, to all appearances it lights istantly).

I realize that electron flow is slow 0.02cm / second?
However, effectively the speed of electricty is c (speed of light) or very near c.
So, if the wires were 186,000 miles long there would be a delay of 1 second between switch ON and light ON.
Additionally, a 1 second delay between switch OFF and light OFF.

If the wires were 1,860,000 miles long there would be a 10 second delay.
(all theoretical, of course. Hence assume NO resistance in the wires etc).

Now the puzzle:
In the circuit the wires are only 1cm long.
But... the entire circuit is 1,860,000 miles away.
There is a bar 1,860,000 miles long - this bar can be used to press the switch ON.
From 1,860,000 miles away you press the end of the bar.
The other end of the bar presses the switch ON.
The light comes on instantly.
NO 10 second delay...

Have we just transmitted a signal TEN times faster than the speed of light?

I think the line now is, "discuss"...

Hoping you can help and/or gives you all something to chat about over a beer or two.
Cheers
Darryl
 
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4472 said:
From 1,860,000 miles away you press the end of the bar.
The other end of the bar presses the switch ON.
The light comes on instantly
Nope. The 'press'ure propagates throug the bar with the speed of sound.
 
Interesting! But there are some thinhs I did not understand. How is the bar placed? Sorry I can't visualize. Wouldn't two such bars be needed(one in forward path and one in return path of the current)?
A diagram would be helpful.
 
Ah ha, thank you BvU !
So, if the bar was 650 miles long (again, in space, no weight etc) and I moved one end 20cm, it would take an hour before the other end moved 20cm?

cnh1995
Only one bar - used to press the switch, and the switch is now 1,860,000 miles away. Imagine having a finger 1,860,000 miles long to press the switch.

Apologies, I have to go out. I'll check in here tomorrow.
 
Done some more research - cheers BvU, answered my puzzle completey!

I'm off to see Star Wars :)
 

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