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# figuring amp

## figuring amp

#1
12-18-03, 03:16 PM
klarson8
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figuring amp

#2
12-18-03, 03:28 PM
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#3
12-18-03, 11:23 PM
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I'm not sure I agree with what this web site says. Ohm's law simply says that through a fixed conductor at a given temperature and possibly some other conditions that the voltage is propotional to current. When one quantity is propotional to another we can intriduce the notion of a constant to make the equation true at all time and this has been defined as resistance.

I don't think that power definition is directly related to Ohm's law although this site seems to think so.

#4
12-19-03, 12:15 AM
Big Jeff
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Twinkle, twinkle, little star,
Power equals I squared R.

#5
12-19-03, 12:31 AM
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That's an interesting way to remember this formula Big Jeff

Seriously though - Ohm's law has nothing to do with power. Power is defined in physics as energy per unit time. After various manipulations of the formula we get the well known P=V*I. This is not part of Ohm's law although the well known V=IR is. We use the first definition and Ohms law to get the Twinkle twinkle.... Simply substitue V=IR in the first equation to get P=(IR)*I = I squared R

An alternate form of course is P=V squared/R

#6
12-19-03, 10:51 AM
charlie b
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For most homeowners, watts divided by volts will give you amps. There are two other factors that can complicate the calculation, but neither is likely to be of importance to whatever project you have in mind.

But first let me ask, are there motors, fluorescent lights, welding machines, or other out-of-the-ordinary contraptions that are part of the “wattage” value. If so, then you must divide “watts” by “power factor,” to get “apparent power” (in units of VA), before converting to amps.

Secondly, let me ask, are you talking about a 3-phase power system (most homes use single phase)? If so, then the conversion to amps is “VA” divided by “volts times the square root of three.”