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I have an adapter which mentions like this...

Input: 100-240V~1.8A

So how much power does it really consume?

I just knew Power = Volts X Current. But not sure how to apply the value since the volts is mentioned as 100-240V the value.

Sorry for a very basic question....

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It's impossible to deduce the actual avarage power consumption from these specification. – leftaroundabout Jun 14 '12 at 10:35

Take whatever your wall supplies (110V, 220V, etc.), and multiply it by 1.8A. Note that this is maximum power usage, not constant.

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110V or 220V is rms, not peak – Mark Eichenlaub Dec 23 '12 at 16:42

I think the specifications represent the range for the proper working of the device. So the 100-240 V should actually mean that the device is able to work fine if the voltage lies within this range. And related to your query about the power consumed, the question arises what part of the power are you actually concerned about, is it the average, instantaneous,active or reactive ?

But I guess this might help you,

for a sinusoidal wave,

$$V(t)=V\sin(\omega t), I(t)=I\sin(\omega t)$$ thus, $P=V(t)\times I(t)=V\times I\times \sin(\omega t)^2$, where $V$ and $I$ are the r.m.s. values.

Accordingly using $V_{rms}=\frac{V_{given}}{1.414}$ and similarly for $I$, and putting $\omega = 2 \pi\times f$, where $f$ represents the frequency.

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