What is the role of voltage in Power?

dknguyen said:

If the light bulb has a fixed resistance you CANNOT keep the current constant while changing the voltage. If you increase the voltage, the current will also increase. The increase voltage AND current will cause increase in power.

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Actually, this might not be a very good example, because this isn't true, especially in the case of a light bulb or any poor conductor. The resistance changes dramatically as the filament heats up. Maybe this is why he's getting confused.

EDIT
nevermind -- I missed the part where you said IF the lightbulb has a fixed resistance -- Sorry! ...And you're BOTH thin-skinned!

Transformers:

We assume ideal initially. Vp*Ip=Vs*Is or Pp=Ps where s and p are secondary and primary respectively.

The devil always hides in the details, but for an ideal transformer this is true. What this says, is that the transformer can help us with power transmission. Houses might like 240 or 120 V at 100 Amps, but there are lots of losses at 20 customers at 100 Amps. the wire would have to be real thick. So, we up the voltage to say 10,000 Volts and we can use smaller wire.

We still have power losses in both wires. A design goal is "usually" around 3%. These designs are at a fixed frequency, so magnetics are optimized.

Transformers can get get hot. Power transformers have oil for cooling and high voltage insulation. There would be losses with frequency too.

The incandescent tungsten light bulb has a cold resistance about 15x lower when the filament is at room temperature than at operating temperature. So, it's a current dependent resistor.

dknguyen said:

I actually did answer your question by talking about Rload separately, despite your spitefulness not allowing you to accept that. Where I am from, Rs is the winding resistance of the secondary and I had to make assumption because you assumed nomenclature was the same everywhere and did not bother to specify what you were actually referring to.

But you will come to learn in your engineering education how to detailed you have to be when communicating with others. You are also going to need to grow a thicker skin if all it takes to be offended is for someone you have never met to not want to add you on Facebook.

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Sorry I was just kidding. Just teasing you, I apologize.

AA, some advice ...

When discussing basic electrical concepts, be careful that you stick to basic electrical parts. There is a HUGE difference between a theoretically perfect transformer which is fine for an entry/medium level discussion of voltages, currents, power, turns ratios, impedances, etc., and *any* real world transformer. If you start getting pushed around about all of the things you're not mentioning, pull the discussion back to the basics.

Never use a light bulb as an example of anything. A light bulb is a resistor with a high parasitic inductance and a huge temperature coefficient. It is a convenient (but dangerous) load for a discussion of AC power, but only if everyone agrees that the light bulb already is on and the line voltage is stable.

Not everyone who knows a lot about electronics knows how to talk about electronics.

The water analogy for electricity is extremely limited. It works well for a grade school discussion of DC; for anything more complex than a flashlight, it sucks.

Reign in your own examples. While there is nothing technically inaccurate with discussing nanoamp currents in high voltage transmission lines, that will be lost on most respondents and you'll get all kinds of flack.

Ohm's Law. Watt's Law. Joule's Law. Know them. See that OL can be used to transform WL into JL. Come to terms with the fact that the four basic quantities (V, I, R, P) are all *interdependent* aspects of anything electrical. This will take a while because some aspects of it are not intuitively obvious.

Before you say something about keeping the current constant while varying the voltage across a fixed resistance, first run some examples through the math and see if it is possible. When you see that it isn't, ask about that. As the quality of your questions increases, so will the quality of the answers.

When running simple math examples, stay away from the quantities 1, 2, and 4 for any of the initial conditions. It can prevent some mislearning (1+1 = 1x1 = 1/1, etc.)

ak