# Speed of electrical cicuits

1. Jan 14, 2010

### Grimble

Hello folks, this may be a very basic question, but if one has a very long electrical circuit, say about 10 light seconds, with a light at one end and a switch at the other, and the switch is thrown, would the light be lit instantaneously?
If not how long would it take?
And what would the effect be, if the connections were cooled to be super conductors?

Grimble

2. Jan 14, 2010

### HallsofIvy

The speed of electricity along a wire depends strongly on the physical properties of the wire and even the surrounding region. It cannot be "instantaneous" of course- it cannot be faster than c, the speed of light, but it can be close to the speed of light. If you were to do every thing you could to reduce resistance, such as using a "super conductor", you could increase the speed but still not to or beyond,the speed of light.

3. Jan 14, 2010

### Born2bwire

It will take something on the order of d/c where d is the length of the transmission line. Electrical signals travel on the order of the speed of light. What their actual speeds are depend on the geometry and material properties of the transmission lines though.

4. Jan 14, 2010

### Grimble

Thank you! That was what I needed to know!

Grimble