# 220 V AC

#### TheSpArK505

Joined Sep 25, 2013
126
Hello Guys.

I have a basic question about electrical outlets. The one in y house outputs 220 V, But since it's AC I believe that it cannot be constant. So what do they mean by 220 ?!!

#### Bernard

Joined Aug 7, 2008
5,719
220 V RMS AC might be 50 Hz or 60 Hz depending on where you are. RMS, ie, root mean square, means that 220V AC will give same heating effect as 220 V DC.

#### Papabravo

Joined Feb 24, 2006
14,857
The relationship between the AC RMS voltage and the peak voltage uses the square root of 2 as follows:

$$V_{pk}=V_{rms}*\sqrt{2}$$

also, a bit of algebra tells you that

$$V_{rms}=\frac{V_{pk}}{\sqrt{2}}$$

In order to compute the RMS value you have integrate the sin function squared over the interval:

$$$0,\pi$$$

#### profbuxton

Joined Feb 21, 2014
419
Basically you are correct. The 220v Ac is not constant. It varies from 0 to 220v * root2 in a sinusoidal fashion(usually).
However, since this occurs at 50/60 times per second(depends where you live) as far as you are concerned its constant.

#### ErnieM

Joined Apr 24, 2011
8,078
Since it is AC it is by definition not constant, but over time, and a short time, the average is constant.

RMS is one way to determine the equivalent DC voltage an AC source is supplying. It mathematically computes the equivalence, so 220 VAC (RMS) would supply the same power as a 220 VDC source to some fixed load such as a resistor.

That does not mean you can use either DC or AC to power any and all arbitrary devices.

(Edited to satisfy the nit pickers. )

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#### profbuxton

Joined Feb 21, 2014
419
Well, you can actually use AC or DC "to power some device".
Incandescent lights, heaters, stoves(non electronic),hot water heaters,universal motors(small fans, power tools etc). Just need to be aware of what is required.