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Crockie


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Electricity 102 for laypeople
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Welcome to number two in this series. Again If this is NOT appropriate please let me know I dont want to be known as the Sheldon of Grey Nomads.

If you need electrical work done on your caravan or RV, get a qualified electrician or auto electrician to do it. Do not ever attempt it yourself, this stuff is dangerous and can kill you!

Lesson 2 Ohm's Law

The laws of nature are pretty much standard across the whole spectrum of physical things. Electricity is no different.

One that must be remembered is Opposites attract: North and South in a magnet, positive attracts negative in electrical. So if opposites attract it follows that likes repel. So negative electrons will attract to the positive pole of a battery. More on that later.

Imagine a large water tank that the level of the water remains constant, if we punch a size X hole in the bottom water will come out (only interested in the volume of water) that volume is determined by 2 factors first the amount of distance between the center of the hole and the surface of the water will give us the pressure and second the diameter of the hole. We will get Y liters per minute flowing.

Now, lets double the size of the whole to 2X. What happens (remembering that the level of the water NEVER changes) is that there will be MORE water coming out. That will be 2Y flowing. So we now see a relationship between pressure and flow.

OK, that is a simple model of Ohm's law.

If I have constant voltage (electrical pressure, potential difference) supply, say a 9 volt battery and I connect a lamp (lamps have resistance) to it (the hole) this creates a resistance, or opposition to the current flow.

Now the tricky part is that if a circuit exists (a path from negative of the battery to positive via the lamp) I will get a current to flow (the volume of the water). The amount of current will be determined by the voltage (in this case 9V) and the resistance of the lamp (size of the hole). OK so lets keep it real simple, IF my lamp is 9 ohms (the electrical unit of resistance) and the voltage we have said is 9 volts a current (volume of water) is 1 ampere (unit of electrical current).

OK now lets increase the size of the hole to 2X.

IF I have a smaller resistance or opposition to current flow it follows that there will be more current (volume of water) flowing. Lets look at a resistance of 4.5 ohms with 9 volts. Ohm's law tells us that if we halve the opposition and keep the pressure the same we will double the current, so by maths and logic the new current will be 2 amps (amperes).

On the other hand if I decrease the size of the hole .5X, smaller hole bigger resistance) the flow (not the spurt out of it) will decrease. So now we have 18 ohms on 9 volts which gives us half an amp or 500 milli amps.

Heres the whole guts

Ohm's law says that "current in an electrical circuit is directly proportional (meaning increase one the other increases too) to the applied voltage, and inversely proportional (meaning increase one the other decreases) to the resistance.

Expressed as a math formula:  I (current) equals V or E (voltage) divided by R (resistance).

Mind you current will ONLY flow if there is an unbroken conductive path between negative and positive.

Now thats a lot to digest, if you wish please ask questions, one or all of us will provide an answer.

Also I would be interested in how many are following these posts, I would not like to be a waste of time on this forum.

No post tomorrow, santa is visiting my caravan with liquid goodies. Merry xmas from me and mine to you and yours: Dougwe and Plendo at Greens, behave or santa will leave you a lump of coal.hmm



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(Phil C) Retired

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oldtrack123


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HI Phil
Well done
Water anoolgies usually work well when explaining electricity
PeterQ

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Crockie


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oldtrack123 wrote:



HI Phil
Well done
Water anoolgies usually work well when explaining electricity
PeterQ

 Cheers Peter. 



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Stratman77


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I applaud Crockie for his not inconsiderable efforts to help educate readers who really want to develop some understanding of basic electrical theory. Especially when there is a plethora of Youtube videos that attempt to achieve the same thing. I have to admit that I have just forgotten much of what I was taught 50 years ago. E.G. I had forgotten the definition of Voltage! I really don't know what refreshing my memory is going to achieve in practical terms, but who knows? The interested folk may find this very simple instructional video:

youtu.be/D2monVkCkX4

with animated electron flows useful in conceptualising what happens when current is flowing. And since nobody has used this old chestnut yet, Ohm Sweet Ohm.

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Chris

Licensed Electrician, Electronics, Gaming & Computer Technician. Now retired and loving it!
Crockie


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Stratman77 wrote:

I applaud Crockie for his not inconsiderable efforts to help educate readers who really want to develop some understanding of basic electrical theory. Especially when there is a plethora of Youtube videos that attempt to achieve the same thing. I have to admit that I have just forgotten much of what I was taught 50 years ago. E.G. I had forgotten the definition of Voltage! I really don't know what refreshing my memory is going to achieve in practical terms, but who knows? The interested folk may find this very simple instructional video:

youtu.be/D2monVkCkX4

with animated electron flows useful in conceptualising what happens when current is flowing. And since nobody has used this old chestnut yet, Ohm Sweet Ohm.

 Cheers stratman77. I have a sticker on the back window of my ute that sums it up

" electricians do with more frequency and less resistance" 

merry xmas



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Stratman77


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Hi, Crockie! Thanks for the seasons greeting. Allow me to extend a Merry Christmas to all readers of this forum. In relation to your sticker, in my case I'm sure I suffer from a permanent short circuit as my conductor was too small and I blew a fuse years ago.....

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Chris

Licensed Electrician, Electronics, Gaming & Computer Technician. Now retired and loving it!
Crockie


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Yeah I blew my HRC rather quickly as well. I now have some p type material where I should have n type.

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hako


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Question from a layperson who knows little and please don't take it the wrong way!.
You say:
Imagine a large water tank that the level of the water remains constant, if we punch a size X hole in the bottom water will come out (only interested in the volume of water) that volume is determined by 2 factors first the amount of distance between the center of the hole and the surface of the water will give us the pressure and second the diameter of the hole. We will get Y liters per minute flowing.

Now, lets double the size of the whole to 2X. What happens (remembering that the level of the water NEVER changes) is that there will be MORE water coming out. That will be 2Y flowing. So we now see a relationship between pressure and flow.

OK, that is a simple model of Ohm's law.

If the hole in the bottom of the tank is 100mm (2500mmsquared) and it is doubled in size to 200mm, the area of the hole is not doubled but squared (10000mm squared)  yet the litres will only double (2Y).

That makes no sense to me - why doesn't the flow quadruple?

 

Regards



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03_Troopy


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If you double the size of the hole in area from 100mm2 to 200mm2 (ie halve the resistance R), you double the volume of water passing through the hole (ie you double the current I)



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Crockie


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I'm trying to use a simple model to demonstrate Ohms law. It's not meant to be accurate in the manner you have suggested. Thanks anyway for reading.

ohms law is a linear function. But I can use another model if it makes life easier. 

model 2

a car is travelling along a flat straight road using X energy to create Y speed. If we don't change the energy and increase the slope of the road upwards the " resistance" by the way of gravity increases thus slowing the car down. Conversely if we go down hill thereby decreasing the resistance the speed will increase. Please remember we are keeping the engine output constant. 



-- Edited by Crockie on Thursday 25th of December 2014 11:26:59 AM

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03_Troopy


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Phil, I don't see any problem with the water model. Sometimes people think too much into it (ie. doubling the size = doubling diameter? doubling area? etc). Doubling the size works OK if you if you think area of the hole. I'm waiting for capacitors, inductors and diodes though

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valiant81


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Hi Phil;

         After you have resistors, capacitors, diodes out of the way, how about a bit of AC theory!!!



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Crockie


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AC theory may be a bit beyond some folks with the trig etc. however I will give it a go, making it simple will not be easy.

Cheers guys for your interest.

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Radar


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Read but sort of under stood. 

Thank you. Ralph.



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