Electricity - PeachParts Mercedes-Benz Forum

Honus · #1 01-27-2014, 10:23 AM

As I mentioned in the thread about CFLs and LEDs, electricity confuses me. Here are two questions I have have never been able to figure out.

First, I can't figure out why this is true:

Quote:

Originally Posted by spdrun

...if the lamp isn't polarized and it's plugged in with hot connected to the socket shell, you can get a tickle when removing a bulb.

Second, what it the hell is alternating current? I understand that the voltage alternates, but what is physically happening inside the wires? Are the electrons vibrating back and forth?

spdrun · #2 01-27-2014, 10:34 AM

Electron flow (current) reverses, going through one cycle 60x per second. Voltage is like pressure, it's what makes the electrons move.

Angel · #3 01-27-2014, 11:25 AM

There is a common metaphor where electricity is compared to water in a pipe. Ampere's/Amperage/Amps/Current are likened to the flowrate of water
and
Voltage/Volts/Potential/Potential-Difference are likened to the pressure at which the water is delivered

This page does it better than I can - Water circuit analogy to electric circuit

imho this metaphor fails when you have an open circuit (the water/electrons dont just fall out the end) or a short circuit (the water/electrons dont just happily run in a circle - the source supplies all the current it can and heats up the wire/connections/batteries until something fails or the source (battery) runs out of current.

To answer your questions:

Lightbulb - house wiring (AC) is not like a battery - the electrician terms are "hot" and "neutral". the hot comes from the pole outside the house, and the neutral is normally grounded - the hot and neutral normally have 120v (rms- its a sine wave...) between them.
You as a person are normally grounded becuase your feet touch the earth - you are normally at 'whatever voltage' the neutral is.
So in the light socket, you have the ring (threaded area) and the tip. normally the tip is wired to hot (its the smallest contact area) and the ring is wired to neutral - so when screwing the bulb in, you *might* touch the ring (which is at the same voltage as you) but you'll never touch the tip (which is 120v different than you)
You'll find the same thing in a car's cigarette lighter plug - the outside of the female end if negative (ground- same voltage as the car chassis ) and the center pin is +12v.

If the socket is wired backward, then the ring will be at 120v and you would get shocked if you touched it.

AC is funny becuase instead of the electrons flowing just one direction, they go from "full speed one way" to "full speed backwards". We did this becuase it is easier to generate and move electricity long distances using AC instead of DC (less loss, simple generating machine...)

The net effect is the same - a Battery (DC) makes voltage, which applied across a resistance/load consumes current (Amperes) and does work (makes light/spins the motor). AC, when applied across a resistance, consumes current and does work.

I like AC becuase you can make unidirectional devices (diodes, AC electric motors) that take advantage of the AC's changing nature and use this to do things that you can't do with DC (example: if you put wrap 2 lengths of wire around a metal bar, you can make a transformer, which easily changes AC voltage up or down with little loss - there are at least 5 of these between your house and the nearest power plant.
if you put DC into a transformer, you'd just make a weak electromagnet.

I'm horrible at explaining these things. Maybe someone else has a better post by now...

-John

spdrun · #4 01-27-2014, 11:28 AM

Good explanation: nit to pick -- we went to A.C. (original systems were D.C., some remnants existed in NYC and Boston till the mid-2000s) because you can transmit it at high voltage (less loss), then transform it down to a usable voltage at residences or business easily. D.C. would have required rotary converters at the time when the power grid was being built -- you could now do it with solid-state switching and transformers, but it's 100+ years later.

whunter · #5 01-27-2014, 06:44 PM

Quote:

Originally Posted by Honus

As I mentioned in the thread about CFLs and LEDs, electricity confuses me. Here are two questions I have have never been able to figure out.

First, I can't figure out why this is true:Second, what it the hell is alternating current? I understand that the voltage alternates, but what is physically happening inside the wires? Are the electrons vibrating back and forth?