Alt-BEAM Archive
Message #00385
To: beam beam@corp.sgi.com
From: Richard Piotter richfile@rconnect.com
Date: Sun, 14 Feb 1999 15:26:40 -0600
Subject: [alt-beam] Re: determining current
This called Ohm's Law. It's the basics of electronics
E=IxR
R=E/I
I=E/R
E
-----
I R
The basic rule is to cover the value you want to find. For example, you want curent:
E
-----
R
E
I=-
R
You must put the values in with no metric prefixes. volts go in as volts, ohms
go as ohms, and amps as amps. if you want to find the current of a 4K resistor
at 10 volts, you use the following:
10
---- = I (answer is .0025)
4000
.0025 Amps is equivalent to 2.5 mA
If you forget what your prefixes mean:
Symbol
/ name multiplier move decimal
|
G giga 1000000000 9 places left
M mega 1000000 6 places left
K kilo 1000 3 places left
nothing 1 0 places
m milli .001 3 places right
u micro .000001 6 places right
n nano .000000001 9 places right
p pico .000000000001 12 places right
The numbers above are what you multiply the number with for the actual value.
3K is 3 x 1000, or 3000
4m is 4 x .001, or .004
Also, if you know the result, such as above, .0025 Amps, you simply move the
decimal point over 3 places at a time.
.0025 A (move the decimal 3 places to the right)
2.5 is the result. Cause you moved it 3 places to the right of zero, you put an
"m" prefix on it.
2.5 mA (you have your answer!)
Say you have 4000 Ohms, and you want to figure that out, you just move the
decimal point left.
4000 Ohms (move the decimal 3 places to the left)
4 is the result. Cause you moved it 3 places to the left of zero, you put a "K"
prefix on it.
4K Ohms (you have your answer!)
If the result were aready close to zero, like 10 volts, 330 Ohms, or 1.3 Amps,
you should probably leave it. Something like .9 Amps can be a matter of choice.
you could say 900 mA, or .9 A. Either way it works. Also, say you have 6300000
Ohms, or .000025 Amps, you move the decimal 3 places, and you have 6300K Ohms or
.025 mAmps. That's still not enough, so you move it 3 more places for a total of
6 places. then you get 6.3M Ohms or 25 uA.
Well, that's the basics I guess!
Richard Piotter
richfile@rconnect.com
The Richfiles Robotics & TI web page:
http://members.xoom.com/richfiles
------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/list/alt-beam
Free Web-based e-mail groups by eGroups.com
Home