2006-07-12 08:58:54 · 6 answers · asked by Marc 1 in Science & Mathematics ➔ Engineering
Why did you ask this twice?
Anyway, Joe has the right answer, but I'll add a little.
Your question says Watts (volts x amps), which is where your confusion came in. Watts and volt-amps are different. Here is how they are calculated:
Volt-amps = Volts X Amps
Watts = Volts X Amps X Power Factor
The power factor is 1 for resistive loads like a light bulb or heating element, so they are the same. The power factor is the cosine of the phase difference, and is never greater than 1, so the watts can be smaller than the volt amps.
Why is this important? Watts is Real power. You pay for real power. Just multiplying volts and amps give you a bigger number than the real power for motors and other inductive loads. The volt-amps are apparent power, and are used for transformers for example, because they need to handle to current (amps). The stress on the transformer, and the wires, is not dependent on the real power of the load, but the apparent power.
Some other answers mentioned average power. It is important to note that both of these are average power. The volts are amps are RMS values (root mean square). The RMS seems strange at first, but it is used because the product of RMS voltage and RMS current is AVERAGE power. If you talk about instantaneous power, rather than average, then you only have watts. Volt-amps and apparent power is a concept, a useful tool, that has no physical reality, and doesn't apply at the instantaneous power level.
2006-07-13 03:05:14 · answer #1 · answered by An electrical engineer 5 · 0⤊ 0⤋
Sometimes Watts = VA, sometimes they are different. When you apply voltage to a purely resistive load (heater, light bulb, etc), then the voltage and current are always in phase. In that case the Watts = VA = volts x amps. When you have inductance or capacitance in a circuit, the volts and amps will be out of phase so the actual power is Watts = volts x amps x sin(phase difference), whereas VA is still just volts x amps. In that second case Watts < VA.
2006-07-12 16:15:26 · answer #2 · answered by Joe 2 · 0⤊ 0⤋
DC power is Watts (volts x amps) because they are in phase (actually static in DC). In AC circuits, the voltage and current can peak at different times (be out of phase) depending on the inductance and capacitance. Then the term kVA or Volt-Amps is more common.
2006-07-12 16:05:09 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Putting it simply, they are arturally the same. What may not be taken into comsideration is the power factor.
2006-07-12 16:04:11 · answer #4 · answered by Brenmore 5 · 0⤊ 0⤋
Joe is right!
2006-07-12 16:38:23 · answer #5 · answered by jimdempster 4 · 0⤊ 0⤋
nothing
2006-07-12 16:02:25 · answer #6 · answered by satanorsanta 3 · 0⤊ 0⤋