Help with physics electricity question.. more of a true or false?

years ago, to my memory my teacher said that electricity travels at about walking speed when you turn your light on. he asked a question, if it travels at walking speed, why do lights turn on instantly when the switch is turned on, the answer he gave was that there were already electrons at the lightbulb and turning the switch moved those electrons. pretty basic. but i am now doing university level physics and have been told that electricity travels at about 1/3 the speed of light





this could be a broken memory or possibly the speed of electricity when powering lightbulbs is lowered immensely but could someone tell me which is true and which is not?





this has bothered me for about 5 years nowHelp with physics electricity question.. more of a true or false?
An individual electron travels along a wire at about walking speed, it's so called drift velocity, at least in a DC circuit. In fact, in an AC circuit, the electron hardly moves at all, just vibrating back and forth. The light switch turns on the light apparently instantly as the wire is kind of like a hose filled with water. Opening the valve at one end discharges water instantly at the other end.





The actual explanation of the propogation time for electricity means we need to think about the speed of propogation of the electron just entering the example hose. The propogation of this effect is depenent upon the propogation of an electromagnetic field.





The propogation of an electric filed however travels at close to light speed (in vacuo) as the propogation is actually the movement of the electrical field, not an electron. The field travels at light speed in the medium, say copper, so the propogation moves at the speed of light (in vacuum) / the refractive index of the medium. So this ends up being about c/3 for most metalic materials.





http://c2.com/cgi/wiki?SpeedOfElectrons





AstrobufHelp with physics electricity question.. more of a true or false?
Both are right.





The electrons that are in the wires and the light bulb do not begin to move until the electromagnetic wave that starts when the switch is closed gets to where they are. For a pair of wires with just air insulation, the wave propagates at the speed of light. With a cable insulated with plastic insulation like the wires in your house, the speed is slower, by a factor of the square root of the dielectric constant, but (1/3)c seems a bit slow to me.
http://www.eskimo.com/~billb/miscon/spee鈥?/a>





http://www.cartage.org.lb/en/themes/scie鈥?/a>





http://www.jimloy.com/physics/electric.h鈥?/a>





From these you will see that there are a number of conflicting thoughts so you are not the only one puzzled.





When I taught physics many years ago I explained this as





the wire is full of electrons


if you push one in at one ned one pops out at the other end very quickly


BUT if you watch the initial electron it takes quite a long time for it to reach the other end of the wire.





Grampa John

brown hair