Switch-to-lightbulb wire delay

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In summary, when connecting wires between two electrical sources, the longer the wire, the longer it will take for the current to flow. The voltage between the two sources also affects the speed at which the current flows.
  • #1
underworld
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Summary: Question about expectations related to electron flow and conductivity.

Here's a question I have... imagine a scientist in a lab. In front of him there's a battery (with typical red/black +/- poles). Behind him is a normal light socket. Now, between the battery and the light socket there are two very long lengths of wire. (Let's say, about 11 million miles or so).

So, the scientist starts the experiment:

1) He attaches both wires to the socket and the battery. He screws in the bulb. What happens?
Now, we all know what "should" happen; or at least what the casual expectation is - which is that the bulb lights up.

But, the question is - when? (Fyi, 11 million miles is the distance light travels in 5 seconds).

Does it light immediately? If so, what mechanism causes it? Shouldn't there be at least a 10 second delay?
Does it light after 5 seconds? After 10? Never?

2) Now, let's say he unscrews the bulb and unhooks all the wires. This time he starts by screwing in the bulb. He then attaches one side of the socket to the wire, and attaches the other end of the same wire to the battery + pole. He waits 6 seconds, then attaches the other wire to the socket and the - pole. Again, we fully anticipate the bulb lighting. But again, when does it light up?

I'm trying to understand what physically happens to cause the electricity to flow. If you were to replace the above with a water pipe analogy, you can determine that source water creates a pressure in the pipe, which, over time, will reach an equilibrium in the pipe. The process of equalizing when more water is added is what causes the flow. Alternately, if you engineer the pipes just right, gravity will pull the water through. So, is there a "gravity" that pulls electrons through un-level wires at some speed? Or is there an "electron pressure" that equalizes in the wire at some speed? You don't expect the water poured into one end of the pipe to immediately come out the other end.

And what are the limits of this? For example, let's make the wires the size of the milky way (about 52,000 light years). So, does the bulb still come on? If so, when? (in other words, is it just a matter of the time it takes to propagate through the wire? or what if you run out of electrons to before any reach the other end?)
 
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  • #2
In the first case the bulb will illuminate immediately, because the contacts of the socket already have a potential difference between them.
In the second case the bulb illumination will be delayed because the socket contacts have no potential difference up to the point when he connects the second contact in the socket to the battery's negative pole. The delay will be broadly commensurate with the length of the wire that makes that connection.

Also, electrons from the battery don't need to reach the other end. It's a wave that reaches the other end. The electrons at the battery end push/shove those ahead of them in the wire and that shove propagates to the other end of the wire and when it reaches it, it pushes some electrons out of the wire and into the bulb.
 
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  • #3
underworld said:
Let's say, about 11 million miles or so
So that is about 44 kOhms for each wire. How many volts is the battery, what is the resistance of the bulb, and how much power does it take until it lights up and burns out?
 
  • #5
andrewkirk said:
In the first case the bulb will illuminate immediately, because the contacts of the socket already have a potential difference between them.
In the second case the bulb illumination will be delayed because the socket contacts have no potential difference up to the point when he connects the second contact in the socket to the battery's negative pole. The delay will be broadly commensurate with the length of the wire that makes that connection.

Also, electrons from the battery don't need to reach the other end. It's a wave that reaches the other end. The electrons at the battery end push/shove those ahead of them in the wire and that shove propagates to the other end of the wire and when it reaches it, it pushes some electrons out of the wire and into the bulb.
The bulb will initially obtain its energy from that stored in the capacitance of the wires. If the resistance of the bulb is less than Zo of the wires, then a wave travels back to the battery, causing it to see a lower resistance and supply more current. The converse occurs if the bulb resistance is higher than Zo. In both cases we will then see the bulb cycling in brightness as waves travel back and forth on the wires, finally settling to a steady value.
 
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  • #6
tech99 said:
If the resistance of the bulb is less than Zo of the wires, then a wave travels back to the battery, causing it to see a lower resistance and supply more current. The converse occurs if the bulb resistance is higher than Zo.
The resistance of the bulb is guaranteed to be less than that of the open circuit that pre-dated it. The initial wave from bulb toward battery is going to cause the battery to see the resistance lowered (from infinity) either way.
 
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Related to Switch-to-lightbulb wire delay

1. What is switch-to-lightbulb wire delay?

Switch-to-lightbulb wire delay refers to the amount of time it takes for electricity to travel from the light switch to the lightbulb. This delay is caused by the length and thickness of the wires used in the electrical circuit.

2. Why does switch-to-lightbulb wire delay matter?

Switch-to-lightbulb wire delay can affect the response time of the light when the switch is flipped. If the delay is too long, there may be a noticeable delay between flipping the switch and the light turning on. This can also impact the overall efficiency of the electrical circuit.

3. How can switch-to-lightbulb wire delay be reduced?

Switch-to-lightbulb wire delay can be reduced by using shorter and thicker wires in the electrical circuit. This allows for faster and more efficient transmission of electricity from the switch to the lightbulb.

4. Can switch-to-lightbulb wire delay be eliminated completely?

While it is not possible to completely eliminate switch-to-lightbulb wire delay, it can be minimized by using high-quality, low-resistance wires and ensuring proper installation and maintenance of the electrical circuit.

5. Does the type of lightbulb affect switch-to-lightbulb wire delay?

Yes, the type of lightbulb can affect switch-to-lightbulb wire delay. LED lightbulbs, for example, have a lower energy requirement and therefore require less electricity to turn on, resulting in a shorter wire delay compared to incandescent lightbulbs.

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