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Ohms Law

THE ESSENCE OF OHMS LAW

by Jud Williams, Performance Power Technologies

A lot of folks do not have a feeling of what the difference is between voltage and current or, for that matter, resistance. And then there is the term "power". Let's look at these terms and work toward a sense of feeling about them.

Voltage is the hardest of the terms to understand because we have developed misconceptions due to hearing the term misused so often. Voltage is merely stored energy and really does not do anything useful. About all we can do with voltage is measure it. The thing that does all the work is current.

Current is well named because it describes what it really does. Look at the current in a river. It is basically the same concept. As current flows, it is capable of doing work like floating some object down the river or turning a water wheel.

Now, voltage does not do that. It just sits there as a potential. For instance, the water held back by a dam is just like the voltage in a battery. The voltage in the battery is not doing anything until something is hooked to the terminals which will allow current to flow. Then it is the current that does the work.

That's simple, isn't it?

As for power, it relates to how much work the current is doing. Take a light bulb, for instance. They are always rated in Wattage and we know that they get very hot. That heat is caused by the current flowing through the filament. The power is then related to the amount of heat that is generated. The hotter an object gets is generally related to the amount of power consumed.

So now we can presume that if a device were to have current passing through it, it would become warm to some degree, if not hot. If we were to increase the amount of current through a device, it would become hotter. How would we cause the current to increase through the device in question? Well, let's say that we are using one battery to begin with and then add a second battery which would double the voltage. This additional battery causes an increase of current through the device we are working with. Let's see how this happens.

And now, we will get a bit technical. This will explain Ohms law and clear up some mysteries surrounding it. Take a resistor of some value such as 10 Ohms. Note that we capitalize the word Ohm. That's because it is a person's name. But to go on with the story, let's apply 12 volts across the resistor. Knowing these two values we can now calculate the amount of current that would be flowing through the resistor. Ohms law states that current (Amperes) is equal to the voltage, divided by the value of the resistor. Divide 12 Volts by 10 Ohms and we get 1.2 Amperes. Remember, we suggested that if we were to increase the voltage by adding another battery, additional current would flow. So let's add another 12 Volts and see what happens. 24 Volts divided by 10 ohms gives us 2.4 Amperes of current, just twice as much as before. Do you think the resistor will get warmer as a result of this?

Remember that the heat is a result of the power consumed by the resistor. Ohms law for power is current multiplied by Voltage. P equals I x E or "pie" (just an easy way to remember the formula). If the current with 12 Volts (one battery) is

1.2 Amperes, we would calculate the power to be 14.4 Watts (Watt is another persons name just as Volta and Ampere are). Now let's again increase the voltage by adding a second battery which we have already discovered increases the current flow. 24 Volts times 2.4 Amperes gives us 57.6 Watts. That is four times the wattage increase for just twice the voltage increase. Now you know why some devices get so hot so quickly.

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Reply to
jsmith
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Stupid comment or whatever. Tell me all you know, it will only take a minute.

And

Reply to
jsmith

{snip}

Does this book also explain how one can employ sheeps' bladders to prevent earthquakes?

Reply to
Bob

Among them, the author of this article.....

Bob M.

Reply to
Bob Myers

Error. Work is heat and heat is work. They are both energy in say, Joules.

Power is Joules per second - Watt.hours = Joules = energy (as in energy consumption.)

Thermal resistance in degrees C / W the W is the heat energy like the kcal.

I'll trust Rich that the rest of this is ok, but a quick scan revealed some grammatical bs down there :)

--
Best Regards,
Mike
Reply to
Active8

No, a lot of folks don't care what the difference between voltage and current is and they know that resistance is futile. It really doesn't make much sense to subtract voltages and currents so why would anyone care what the difference is?

No duractance is the hardest to understand. It is very important in the creation of inverse reactive power for the sychronization of grammeters.

The EER guy will be alarmed to hear that soring energy does not do anything useful. Storing energy is what he has been selling for years.

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kensmith@rahul.net   forging knowledge
Reply to
Ken Smith

  • the pressure.

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Reply to
Spehro Pefhany

Why use analogies at all? There are no really good ones. It's easy to explain things in real terms; all you have to do is accept that particles can have charge and that materials can have resistance.

John

Reply to
John Larkin

No, we don't, not how you/he just mis-used it.

The convention is to use an upper case letter when using the single letter abbreviation for the unit, such as V for volts, but not when the name of the unit is spelled out in full. Since a Greek letter is used for our single letter representation of ohms, we only use the upper case when talking about the man, e.g. Ohm's law.

Similarly, the abbreviation for ampere or amperes is A, whilst the man is referred to as Ampere.

Reply to
dB

No, resistance is V/I :-)

Hey, give the guy a break. He's attempting to prove we really *are* being conned by the power companies. ;-)

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"What is now proved was once only imagin'd." - William Blake, 1793.
Reply to
Paul Burridge

How many children understand water pressure and flow through pipes? And if you tell them that water flow rate is proportional to pressure difference, you are lying to the poor young souls.

John

Reply to
John Larkin

Watt you may encounter is some potential resitance to your current conduct.

Bob

Reply to
Bob Stephens

I prefer the hose pipe analogy.

The pressure of water ie how far it squirts, is voltage. The amount of water per second is currrent. The size of the hose is resistance. Power is the rate at which water is coming out.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org
Reply to
Dirk Bruere at Neopax

Hell I'll tell you all we BOTH know it won't take any longer !!

-- Regards ........... Rheilly Phoull

of

prevent

Reply to
Rheilly Phoull 

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Ever do a belly flop?^)
Reply to
John Fields

Sez who????

Reply to
jsmith

Aw geese, grovel, grovel !!

Reply to
jsmith

I have long promoted the milliHelen, the unit of feminine beauty sufficient to launch one ship.

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 Thanks,
    - Win
Reply to
Winfield Hill

Because when children come across it for the first time it is not intuitive. If it was trivially obvious it would not be named after Ohm. Analogies are very helpful.

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org
Reply to
Dirk Bruere at Neopax

Just as the article stated . . . . ESSENCE . . . . .most folks do not have a "feeling" about the difference between voltage and current . Many things I have read misuse the two words or interchange them so as to not make any sense at all. So what does 120 volts alternating current mean???? Are we talking about volts or current? How about 120 volts, alternating voltage (as seen on a scope) Go figure!!

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Reply to
jsmith

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