Current Electricity

polishpaddy

[FONT=Arial,Helvetica,Univers,Zurich BT][SIZE=-1]Current Electricity -- A constant flow of electrons.
Direct current (DC) means the electrons move in one direction.
Alternating current (AC) means the electrons flow in both directions.




Say this circuit uses dc. How do the electrons move in this circuit? I'm a bit confussed on things such as do the electrons go anti clockwise ?

Whats the minus terminal for exactly? Do electrons come out of that too? See i'm confussed



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watty

When current was discovered they didn't know about electrons, which are negative.

The electrons always go from - to +, the opposite direction of current.

Some semiconductors the electrons move slowly with a gaps like bubbles in a water pipe moving faster in the direction of "current". These are called "holes".

See http://en.wikipedia.org/wiki/Electric_current#Conventions

polishpaddy

When i was finished reading the link you provided to me, you inadvertently brought up more questions for me when you mentioned bubbles called holes.

How is the abstraction achieved in computer science for binary 0 and 1?

Gurgle

polishpaddy wrote: »

How is the abstraction achieved in computer science for binary 0 and 1?

Binary 0 and 1 are representations of the voltage present at a point in a digital circuit.

0 = Ground (0V)
1 = Vdd, i.e. whatever your power supply voltage is

Generally, when the voltage is in between 0 and Vdd, the interpretation is 0 if its less than Vdd / 2, 1 if more.

polishpaddy

I think thats a great answer. Seems to be all comming together now.
The mind boggles when you try to think how it all works.

watty

Logic normally has 1= true, 0 = false.

But ECL, a current may be "1" and no current "0"

There have been many ways of implementing logic cicuits:
Relays (late 1930s to early 1940s)
Valves (or Tubes USA) (mid 1940s to early 50s)

Resistor Transtor Logic (RTL)
Diode Transistor Logic (DTL)
Emitter Coupled Logic (ECL)
(The techniques of these last three are still in use in a limited fashion)

Transistor Transistor Logic TTL (first mostly 5V family, but less than 0.8V is 0 and more than 1.8V is "1" so poor "noise immunity")

many families now:
CMOS (originally 15V, now can be under 1.2V), NMOS, HCMOS. S-TTL, LS, ALS, FAST.

Some logic gates today use only 1.1V supply to reduce power consumption and increase speed.

Speeds have increase from 0.1MHz to over 25,000MHz for individual gates.

usemyillusion12

does the current not flow from + to - , as the + terminal is the high potential terminal and - being the low , thus the current flows from high to low ,

electrons themselves do move , however they move slowly , this is called the electron drift velocity. the usual velocity of the electrons can be comparibe to a caterpillar

current electricity is the flow of electric charge

Michael Collins

usemyillusion12 wrote: »

does the current not flow from + to - , as the + terminal is the high potential terminal and - being the low , thus the current flows from high to low ,

electrons themselves do move , however they move slowly , this is called the electron drift velocity. the usual velocity of the electrons can be comparibe to a caterpillar

current electricity is the flow of electric charge

Yes the "conventional" current flows from + to -, but the electrons themselves move from - to +. This isn't the contradiction it seems to be! If you look at how current is defined, you'll see it is the amount net positive charge that passes a given point per second (hence the units of coloumbs per second).

So if protons or positive ions were the carriers of this charge (as happens in some cases), then they would flow from + to -, just like the resulting current. But when we talk about electrons moving (as is always the case in metals) or even negative ions, because current is defined in terms of positive charges, to get a current from + to -, we need movement of this negative charge from - to +.

Yeh, the time it takes an individual electron to get from A to B is quite a bit larger than most people expect. For example, for an electron to move across a standard 1 m peice of wire would take about 17 minutes!

usemyillusion12

Michael Collins wrote: »

Yes the "conventional" current flows from + to -

yes , sorry , this is what i was thinking about