speed of electrons in a car circuit? 10 points for first good answer!?

Question

When you turn a key to start a car, electrons migrate from positive battery terminal through the electric network to the starter motor and back to the negative battery terminal. Estimate the time this takes. (show me how you did it)

when turning a key to start a car, electrons migrate from the negative battery terminal through the electric network to the starter motor and back to the positive battery terminal. Estimate the time it takes. (show me how you did it) I had neg and pos switched sorry!

Answer 1

Assume a 12 volt battery that gives 60 (coul/sec) current flow (amps). If 180 coul charge flowed through from one terminal to the other. Your time is then t = q (coul)/ I(amps) = 3 seconds.

In the winter, we can suppose 600 coul charge, and 60 amps, which gives a time of 10 sec, this is true since it takes longer for the car to crank up in the winter... colder temperatures means slower chem reaction in the battery.

Answer 2

Interesting question. The "time" is so little that for all practical purposes, it's non-existent.

The individual electrons actually move quite slowly, however, the electrical power transfer travels at light speed.

Lets do it any way - first the key is turned and energizes the starter solenoid (estimate 10 feet of travel to starter, another 10 feet from the positive battery terminal to the switch for a total of 20 feet) the return path to ground in the body chassis - oh, about another 8 feet.

That's a total travel of 28 feet. Light travels at 186,000 miles per second, that's 982,080,000 feet per second. At that rate, it's doing the 28 feet in about 2.85e-8 or 0.0000000285 seconds.

I think it's a bit slower on a cold, Maine, January morning - or maybe it just seems that way.

Answer 3

Actually, current/charge flows from negative to positive.