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Your First Valuable Law in Theory.

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Author Topic: Your First Valuable Law in Theory.  (Read 9238 times)
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« on: June 05, 2005, 04:16:22 PM »

Good Day,

 I'm Jack Call is KA3ZLR, or ZedLR as i liked to be Refered to, and my First presence in the Amateur Service has always been Technical Investigation and Experimentation so this covers alot of territory but always no matter where i go or what i'm doing alot of it refers back to the building blocks in Electronic Theory, which there are many, and understanding the begining  building blocks will make the more advanced Theorys and Functions easier to grasp and work with.

 In all handbooks and in this one we will touch on Ohm's Law, as stated:

 The values of current, voltage and resistance in a circuit are by no means independent of each other. The relationship between them is known as Ohm's Law. It can be stated as follows:
 The Current flowing in a circuit is directly proportional to the applied EMF [Electromotive Force] "The difference in electric potential , or voltage between the terminals of a source of electricity and is usually measured in Volts" to continue, and is inveresly proportional to the resistance. Expressed as an equation, it is:

I [Amperes] = E [Volts] Divided by R [Ohms]

 The equation gives the value of current when the voltage and resistance are known. It may be transposed so that each of the three quanties may be found when the other two are known:

E =IxR

(that is, the voltage is equal to the current in amperes multiplied by the resistance in ohms) and

R=E divided by I

(or the resistance of the circuit is equal to the applied voltage divided by the current).

 All three of these equations are your first best building blocks and there are others to learn,  it must be remembered that the quantities are in Volts, ohms, and Amperes: other units cannot be used in the equations without first being converted.

 So give Ohm's and his Laws a good read and learn to understand them very well and you can't go wrong in trouble shooting and designing circuits.

Be Well... ZedLR.
Steve - WB3HUZ
« Reply #1 on: June 05, 2005, 04:33:29 PM »

The circle below can be used as a memory aid. Any derivation of Ohm's Law can easily be found. For example, using the second circle below, you can easily see

I = E/R


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Posts: 311

« Reply #2 on: June 05, 2005, 06:13:14 PM »

Here is a memory aid I learned in the Navy long before I went to engineering school.

E = Eagle (the bird)
I = Indian (Native American)
R = Rabbit (little furry creature)

Well now if you want to find for the voltage (E) then you assume
that be the eagle. Now the eagle looks down from the sky and sees the
Indian and the Rabbit on the same level that being the ground so E=IR.
Now say you want to figure out what the resistance is well you be the rabbit and the rabbit looks outa his eyes and sees the eagle up in the sky above the indian so that must be R = E/I

Do you get the picture?

By the way the Navy also taught me "ELI the ICEman".
Now this tells me that for AC in an inductive circuit (L) the Voltage (E) leads the Current (I) and in a capacitive circuit (C) the current leads the voltage. This phase angle relationship is quite useful but ofcourse in a purely resistive circuit the voltage is always in phase with the current.
I think?

Best Regards

Regards, Q, W1QWT
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Posts: 1782

CW is just a narrower version of AM

« Reply #3 on: May 31, 2006, 08:52:54 PM »

My 9th Grade shop teacher in high school also taught me Ohms Law, but he made us construct a device, just in case we "didn't get it".

He called it the Handi Tester and I think it was out of an old electrical shop book.
Basically it was out first electrical shop project.

The device consisted of an NE-2 bulb and two 100K resistors (one on each leg) shoved into a drilled out wooden dowel. A little hole was put up near the bulb. A pair of 24 inch test leads and some test prods were attached and a wooden grommet was stuffed in the bottom, thus securing the assembly and leads. The whole thing was coated in Deft, a common wood finish which was made from a powder mixed with water.  It must have been a good design because, even though a stole the test prods off it, I still have it and it still works!

Anyway the thing would tell you if you had voltage greater than 60- 80 Volts. That was Handy.

It seemed to work fine up to 220 V too and I suspect it would work higher before getting too bright and blowing up.

The neat thing was that on AC, both of the electrodes lit up , but on DC only one lit up. So you could tell AC from DC.

Mike WU2D

These are the good old days of AM
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