3

This question is similar to:

  1. Doesn't Veritasium's Recent Video About Circuits Violate The Speed Of Light?
  2. In what order would light bulbs in series light up when you close a long circuit?,

but seeks to build upon them.

Veritasium source question link:

https://www.youtube.com/channel/UCHnyfMqiRRG1u-2MsSQLbXA/community?lb=Ugkx0is4qHkf1fIgTCpW2A_zu5wbJuObvflK

Copied here:

,_____|L|_____,    _
|             |    | 1m
\_____|B|_/ __/    -

|-------------|
  1 lightyear


L = Light bulb
B = Battery

Part 1

Would the result be different if there existed a "perfect insulator" of infinite "height out of page" in between the cables? eg:

,_____|L|_____,    _
|~~~~~~~~~~~~~|    | 1m
\_____|B|_/ __/    -

|-------------|
  1 lightyear


L = Light bulb
B = Battery
~ = perfect insulator

Part 2

Clarification question on article #1:

Would the following also turn on in $1m/1c$ (assuming the switch and the battery were $1\,\mbox{m}$ apart)?

,_____|L|_____,    _
|             |    |
|             |    |
|             |    |
|             |    | 1 lightyear
\_____|B|_/ __/    -

|-------------|
  1 lightyear


L = Light bulb
B = Battery

The part that feels wrong about #2 it would appear to allow near-instant transfer of data one way.

ListsOfArrays
  • 133

1 Answers1

3

Part 1

An insulator wouldn't isolate the electromagnetic fields. "Insulator" only means the material doesn't have many free charges, so it won't affect or be affected by the electromagnetic fields so much. Notice, for example, that the air is an insulator, and the light bulb still turned on quite quickly. If you put a conductor, on the other hand, the electromagnetic fields would move around the free charges and that could affect the propagation of the electromagnetic wave. If the conductor is thick enough, the fields would vanish before being able to trespass it. Think of a Faraday cage: no electric fields are allowed inside a conductor, meaning putting a big wall of metal between lamp and battery would cause you trouble, since energy would not be able to trespass the wall (it would be absorbed by the wall instead).

Edit: as mentioned by Andrew on the comments, putting a "conducting wall" will slow down the time it takes the lamp to light up only if this wall is isolated from the circuit. If the lamp and battery are connected to the "conducting wall", current might flow directly from the battery to the lamp and the system gets considerably more complicated.

Part 2

If the distance is one light-year, the time for the lamp to turn on would be roughly one year. Information is not traveling arbitrarily fast: it is being carried by the fields, which can only transport energy and information at the speed of light.

Níckolas Alves
  • 17,567