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### Topic: Electronics formula's (Read 4963 times)previous topic - next topic

#### Morrolan

##### May 25, 2011, 01:47 pm
Hi,

I'm interested in finding out what common formula's people use on a regular basis, eiether electronic or electrical.

The common ones are Ohms Law(v=IR), Watts Law (P=IV - don't know if it is actually called Watts law), potential dividers (Vout = R2/(R1+R2) xVin) etc.

Are there any other formulas that people use on a regular basis?

#### TerryKing

#1
##### May 25, 2011, 01:55 pm
I used R-C time constant  T=R*C  twice today...  But mostly ohm's/watt's

#### Morrolan

#2
##### May 25, 2011, 02:06 pm
Many thanks for that Terry.

Anyone else?

#### bubulindo

#3
##### May 25, 2011, 03:18 pm
P = UI
T = RC
U = RI

And I think it's about it.
Knowing the voltage drops in LEDs to calculate the current going through a LED is also good to know, but I mostly don't care and go for a 1k resistor with 5V.

Can't think of any more formulas for small electronics, since all the other more complicated deride from these. :\
This... is a hobby.

#### Morrolan

#4
##### May 25, 2011, 03:32 pm
Bubilindo, I know the T=RC formula - please could you explain the others as they are new to me?

Regards,
Morrolan

#### tastewar

#5
##### May 25, 2011, 04:00 pm

...
Can't think of any more formulas for small electronics, since all the other more complicated deride from these. :\

I think you mean "derive," (he said derisively...) :-)

#### floresta

#6
##### May 25, 2011, 04:07 pm
Quote
Bubilindo, I know the T=RC formula - please could you explain the others as they are new to me?

Substitute an 'E' or a 'V' for his 'U' and they should look familiar.

Don

#### Morrolan

#7
##### May 25, 2011, 04:13 pm
Haha, I hadn't even clicked that there were just different versions of V=IR and P=IV!

Any others?

#### Grumpy_Mike

#8
##### May 25, 2011, 06:49 pm
1/ (2pi Sqrt(LC)) - is the resonant frequency of an LC circuit

1/ (2pi FC) - is the capacitive reactance (equivalent resistance) of a capacitor at a frequency F. Replace C with L for inductive reactance.
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#### johnwasser

#9
##### May 25, 2011, 07:16 pm
De Morgan's laws are helpful in designing digital logic:

NOT (A AND B) == NOT A OR NOT B
NOT (A OR B) == NOT A AND NOT B

That means that even if all you have is a big pile of NAND gates (or NOR gates) you can build anything.
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#### Grumpy_Mike

#10
##### May 25, 2011, 07:19 pm
Not so much a law as a theorem.

#### johnwasser

#11
##### May 25, 2011, 07:46 pm

Not so much a law as a theorem.

You'll have to edit the Wikipedia article:
http://en.wikipedia.org/wiki/De_Morgan's_laws
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#### Grumpy_Mike

#12
##### May 25, 2011, 11:49 pm
Ok looks like I will have to. A law is reserved for physical phonemna you don't talk about Pythagrous' law do you. Or perhaps you do?

#### keeper63@cox.net

#13
##### May 26, 2011, 12:03 am
When I went to tech school here in Phoenix, one of the things we were given as a part of our toolkit was (IIRC) a small folding "booklet" of equations for electronics, from - once again going from memory here - Graymark. I'll have to dig it up when I get home tonight...
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#### Grumpy_Mike

#14
##### May 26, 2011, 05:24 am
Then there is:-
Q = VC
Where Q is charge in coulombs, V is voltage and C is capacitance (in Farads)
One coulomb is the amount of charge that flows past a point in 1 second when the current is 1 Amp.

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