Watts from ohms one line

[steve66]

You should be able to find tons of examples and explanations on the internet. Google basic DC circuits, or parallel DC circuits, Series DC circuits, and even parallel-series DC circuits.

They are all solved using a fairly similar process - you simplify the circuit by combining combinations of parallel resistors and series resistors until you get to a single source and a single resistor. (Yes, voltages in series can also be combined by adding their voltages.) This may take several steps - the key is being able to see which resistors are truly in series, and which ones are truly in parallel.

Use the simple circuit to find the total current flowing.

Then work backwards, expanding the circuit and calculating current through each resistor and voltage across each resistor until you get back to the original circuit.

With a little practice, a circuit like this one is easy to do in your head.

 

[steve66]

Here is an example. Find all the currents through the resistors, and voltage drops across the resistors.

 

[4x4dually]

Oh, well. So much for having the OP figure it out for himself.

After 27 post with hints in every other one, I figured it was time for an explanation. If he can't figure it out after that many hints....probably wasn't going to.

"Sorry I had a fight at your blank pantha party"

 

[jim dungar]

The only main issue I was having was getting the total ohms. I thought all resistors represented a load like a light bulb.

This was the question you should have asked first, then we would have known your experience level.

You asked us for our answer. You didn't even tell us what your answer was. So we just gave hints which turned out not to be very helpful.

 

[petersonra]

Ok, man last time I ask a question on here , thanks for your input.

It is not a dig at you personally but rather an observation on how poor apprentice training can be some times.

That someone managed to get through a five year electrician apprenticeship without have a good understanding of Ohm's law in practice is just sad. But, I see it over and over. And it is not like the electrician apprentices are stupid. They could learn if someone was teaching it.

 

[Sea Nile]

It may help to think of it like water in a hose. If you have two points in the hose that the flow is restricted connected in series each restriction will slow the flow,.

But if you had a Y fitting feeding two different hoses running parallel to each other. And each of those hoses had the same restriction, then the two houses went through another Y fitting back into one hose, you would have half of the total resistance to the water flow.

 

[Rjv0858]

Thanks for all the help , no one has ever explained any of that to me.

 

[LarryFine]

Thanks for all the help , no one has ever explained any of that to me.

A simple explanation of Ohm's Law: One volt is capable of pushing one amp through one ohm.

If you increase the voltage and/or reduce the resistance, the resultant current increases proportionately.

A simple explanation of "Watt's Law": One volt pushing one amp (through one ohm) produces (or consumes) one watt.

Everything else we've been discussing merely involves manipulating these values with simple math.

Don't get confused by the difference between applying a different voltage to a given piece of equipment . . .

. . . and . . .

Equipment designed to produce (or use) a given amount of power when supplied by a different voltage.

 

[Tulsa Electrician]

Here is some shots from a book I have.
If you notice on the last page there was a printed error. As you work thru the example always check the circle. They printed E squared x R = W. That was wrong.

I feel your pain. Sometimes I get mixed up as well. Something to look at is, Kirchoff's Law. It is mentioned in the first pic ( page 21). Good luck on your test.

 

[Sea Nile]

There is a new edition of the electrical theory book scheduled to be released next month.
www.mikeholt.com/ComingSoon
This was an amazing resource for me and will give you the foundation to really understand why electricity does what it does.

 

[4x4dually]

It may be a simple little picture, but it is a good visual. It can be used to explain water flowing in a pipe as well. Voltage is to pressure, as current is to flow, as resistance is to restriction.



The way I memorized ohms law when I started college and took ECT 1104 back in 1992, was to think of the Eagle, the Indian, and the Rock. E is often notation for Voltage, I for current, and R for resistance.

Eagle = R * I (the eagle sees the Indian and the rock V=R*I
Indian = Eagle / Rock (the Indian sees the Eagle over the rock I=V/R
Rock,= Eagle / Indian (the rock sees the Indian over the rock R=E/I

Dumb enough I know, but it helped me back in the day.

Same for Geometry. Sell One Horse, Catch Another Horse, Trot On Away

Sin=Opp/Hyp
Cos=Adj/Hyp
Tan=Opp/Adj

And the same holds true for the colors of the resistor color code wheel.

Bad Boys Rape Our Young Girls But Violet Gives Willingly
Brown, Black, Red, Orange, Yellow, Green, Blue, Violet, Grey, White. 0,1,2,3,4,5,6,7,8,9

 

[GoldDigger]

Bad Boys Rape Our Young Girls But Violet Gives Willingly
Brown, Black, Red, Orange, Yellow, Green, Blue, Violet, Grey, White. 0,1,2,3,4,5,6,7,8,9

Extended form:
Bad Boys Rape Our Young Girls But Violet Gives Willingly for Silver and Gold.

 

[4x4dually]

Silver, Gold, and RUBYS!!!

Thanks. I'll have to remember that.

I do have my little cheat wheel dohicky on my desk though. I got it when I started college. It's seen a few days.

 

[retirede]

Extended form:
Bad Boys Rape Our Young Girls But Violet Gives Willingly for Silver and Gold.

I had a teacher use that in front of a class (1978). There was one woman in the class and she went ballistic. Went to the dean, etc. of course back the, nothing ever came of it.

The PC version is “Better Be Right Or Your Great Big Venture Goes West….”

 

[rambojoe]

I liked the birth canal analogy of ohms...we come into this world as 8.0 amps

 

[Carultch]

Yes I know all about that , what I didn't know is how to find total resistance of parallel loads. The equation made no sense to me , now I understand it. Thanks for the help

The way that it works, is that resistance adds up in series, while its counterpart, conductance, adds up in parallel. Conductance is defined as the reciprocal of resistance. So to combine resistances in parallel to get equivalent resistance, you first take reciprocals of all the resistances to get conductances, add up these conductances, and then take the reciprocal of the sum total of the conductance, to get equivalent resistance.

For the case of identical resistances in parallel, the resistance of the combination is just divided by the total number of them in parallel.
For the case of two resistances in parallel, the formula reduces to "product over sum".

 

[ActionDave]

I am always amazed at how poorly electrician apprentices are taught the really basic stuff about electricity. This should have been something the op figured out in his head in about ten seconds.

The other issue that just makes me crazy is how few electricians can actually read electrical drawings and understand them.

I am a good electrician. I suck at reading drawings and I suck at math. I mean I really, really suck at math worse than I suck at reading drawings. I'm a hands on guy. I learned the electrical trade by doing it on the job, not by studying it at a desk inside. I was lucky that I fell in with a fantastic boss who was a second generation electrician and he taught me well. I understand the concepts and electrical theory quite well. I understand Ohm's Law as far as how volts, amps and resistance interact, but to get the right answer on a test where I have to calculate resistance in a series/parallel circuit..... no doubt I'd flunk. And I don't care. I'm good at what I do and I enjoy it.

Having said that I will agree that there needs to be better education for apprentice electricians so that they do have a solid understanding of electrical theory and the NEC. It's the best way to elevate the trade so that we get better pay, do better and safer installations, and don't get pushed around by lousy inspectors.

 

[Russs57]

"The only main issue I was having was getting the total ohms. I thought all resistors represented a load like a light bulb".

True enough. But once you close SW 3 you have two just connected a neutral to the other side of the two 10 watt bulbs in parallel. The rest of the "light bulbs" are no longer in the circuit as they are connected to the neutral on both sides of them. The two 10 ohm loads now equal one 5 ohm load.

The question would have been a lot more difficult if the resistor weren't equal values and they asked you what the watts were as each switch was closed. If you are game, close 1 and 4 and you have 5 ohms for the first pair, plus 5 ohms for the next resistor, plus 10 ohms for the next pair....10 times 10 times 20 equals 2,000. Now close 2 and the two 20's go away so that is ten less ohms so 1,00 watts. Close 3 and 5 more ohms goes away so 500 watts.

Back to your problem, the formula is amps time amps time resistance. So 10 amps X 10 amps X 5 ohms equals 500 watts

The guys here may "seem" like Dicks sometimes but they are the total opposite. They are going to challenge you to think and they are going to ask leading questions to see what your knowledge level is so they can respond in a way that you can comprehend. Stay with them as you won't find a better forum

If I said 10 times 10 times five equals 500 you wouldn't have learned anything even though I gave you the answer you requested.


PS I'm not an electrician and I think this forum rocks (although I might understand a lot of electrical concepts better than many so called electricians). Heck one of my questions holds the record for the most responses (I think that is still true). You want to gain some respect, come back with your solutions for different switches closed with all resistors being different values. Work with prime numbers for each resistor value (which makes it a PIA). Your decision to rise to the challenge. I think you will find such practice pays handsome dividends over the years.

 

[ggunn]

I am always amazed at how poorly electrician apprentices are taught the really basic stuff about electricity.

The same can be said about many inspectors.

 

[petersonra]

The same can be said about many inspectors.

I deal with a lot of electricians but few if any inspectors.