Thank you. You have supplied the most comprehensive response.
First, let me say that as far as I can tell, the "water analogy" that is commonly used is inaccurate.
Volts are joules per coulomb: J / C
A joule is: mass times distance divided by time: 1 kg * m**2 / s**2
A coulomb is the amount of charge in 6.241 X 10**18 electrons.
Thus, volts are a ratio of energy within an amount of time to a specific amount of charge.
Thus pressure (e.g. pounds per square inch) is not analogous to volts because volts include time.
An ampere is a coulomb per second: 1 coulomb / 1 second
which is a subset of the information in volt.
Thus, and obviously I am not an expert, all the miscellaneous ratios seem redundant and obfuscating.
Would it not be better to express electrical situations in terms of joules and coulombs and
disregard this plethora of redundant and obfuscating ratios?
"... sometimes people are just sloppy in their thinking"
Yes, very much so, and sloppy in their learning and, if it befalls them, their teaching too.
"Then we have:
I, current, which is measured in amps"
Amperes actually,"amps" is part of the sloppiness to which you refer. The same sloppy abbreviation also means amplifiers.
"But, where it really gets weird is "wattage" "
Power actually.
"It seems completely redundant and obfuscating of the volts and ohms measurements."
Of course it does - to you. As you say. you "don't understand why the concept of watts exists."
"I don't understand the logic of watts.
Watts seems to be a nonsensical, redundant number.
Could someone explain the usefulness of watts?"
Yes, but let's not jump the gun.
It sometimes helps to use the electricity/water analogy.
Consider two hydraulic systems, a garden hose-pipe and a wide river.
They both carry water. The rate at which it flows in, say, gallons per second, is a measurement of the current of water.
In electricity, current is measured in coulombs per second; a coulomb is 6.241×10^18 electrons, and 1 coulomb per second is called 1 ampere.
For current to flow, either in a hydraulic or an electrical system, there has to be a pressure difference between the extremes of that system.
In our garden hose, the pressure comes either from a pump or from the difference in gravity (height) between a storage tank and the hose's end. In the river it is the difference in height of the source and the point of measurement.
The pressure in a hydraulic system might be measured in p.s.i. (pounds per square inch). In an electrical system it is measured in volts.
The flow/current of water can drive turbines. This represents power - the power of the flowing water.
Power is sometimes measured in h.p. (horsepower). The concept of horsepower is, wouldn't you agree, useful?
In electricity it is measured in watts. And I think the the concept of watts is useful too. It's a measure of the electrical power which something uses.
And, while I'm at it. Let's consider the domestic wiring in a house, We need to know the voltage of the system, and we need to know the current capacity of the wiring. It's resistance must be low enough to be insignificant at its rated current, so it is irrelevant in that scenario.
If I tell you that "this circuit" has a capacity of 15A (the abbreviation of amperes), it tells you something useful.
If, in the (very unlikely) event that I tell you that it's a 110V source and the wiring has a resistance of 2 ohms, THAT is completely useless information.
current (measured in amps) is what is actually moving in the circuit.
Watts is a measurement of real power. Electrical equipment uses a certain amount of power to operate. A 60 Watt bulb will draw 60 watts of power in order to operate. Your utility company will combine real power with time (energy is watts X hours) in order to determine what your utility bill will be each month.
Most circuits are more than a simple resistive circuit (inductors and/or capacitors are included in most circuits) so that is what resistance is not usually used to define a circuit.
In most instances circuits have a known, constant voltage. For instance it customary voltage in American residential applications is 110 volts. It is know and it is constant and that is why it is typically not used to define a circuit.
The real reason that current is used to define a circuit is because all electrical equipment is limited by the amount of heat that the equipment can withstand and operate normally. Current running through a circuit cause heat to build up. The more current flowing, the more heat is built up. This thermal limit is defined by the amount of current required to cause that temperture limit to be reached. If you have a 15 amp circuit, then one piece of equipment will overheat if more than 15 amps flows in that circuit.
So to answer your question. The reason current (amps) is used to define a circuit is because all circuits are limited by heat, and the amount of heat is determined by the amount of current flowing in a circuit.
It's important to realise that Volts, Amps, etc are just the electrical units and there are similar units for mechanical systems that do the same. A Watt or Joule is defined first in terms of Newtons and meters and seconds. Voltage is electrical pressure, ie force. Amperes is electrical movement. In both systems power (Watts) is the product of force and movement, and times time is energy (Joules). Eveything, including electrical units is defined in terms of killograms, seconds, meters, and coulombs. Be sure you understand that acceleration (force) is the derivative of velocity and velocity is the derivative of distance, wrt time.
http://en.wikipedia.org/wiki/SI_derived_...
Since you totally misunderstand the concept you are deriding - please do not go shopping an extension cord to run a power saw or install wiring to meet code - both of which require knowing the amps to be used and actually the distance to the tool in the case of an extension cord. If you get it wrong the wire will heat up and melt or a circular saw will slow down and burn out the motor wiring.
"Why not just be specific and specify the amount of volts and ohms in the circuit"
thats great if you know the volts and the ohms
but what if you dont?
I'm having trouble understanding the difference between volts, ohms, amps and watts.
As many people know:
V, voltage is measured in volts
r, resistance is measured in ohms
This all seems logical and useful.
Then we have:
I, current, which is measured in amps
amps = volts / ohms
OK... I'm thinking a little bit of "so what".
Obviously it is more enlightening to know specifically what volts and ohms are in place.
I'm not sure why you would want to obfuscate that information by putting it in a single number like amps.
But, whatever... sometimes people are just sloppy in their thinking and like to summarize.
But, where it really gets weird is "wattage" (W):
watts = volts X amps
I don't understand why the concept of watts exists.
It seems completely redundant and obfuscating of the volts and ohms measurements.
watts = volts X (volts / ohms)
I don't understand the logic of watts.
Watts seems to be a nonsensical, redundant number.
Could someone explain the usefulness of watts?
And for that matter, while you are at it... why do we need amps?
Why not just be specific and specify the amount of volts and ohms in the circuit?
If someone tells me I'm looking at a 15 amp circuit, my first thought is...
"Well now that you have wasted my time by telling me some completely useless information,
can you tell me the voltage and resistance of the circuit?"
Thanks
