the different between Vpeak, Vpk-pk,Vrms and V means ?

Ok. I understand. 我是電機工程畢業的，希望幫到你。我會盡量深入淺釋

Let's consider a simple sine wave curve. y = 3sin(x). We know the maximum value of y is positive three and the minimum value of y is negative three. the reason is that the value of sin(x) is between positive one and negative one.

Now, consider V= 3 sin (wt). The y-axis is voltage V and the x-axis is (wt) (Omega t).

1)
Then the peak voltage (Vpeak) is 3V because no matter what (wt) is, the maximum value of V is POSITIVE THREE (+3V).

2)
Peak-to-peak voltage (Vpeak to peak) is 6V because the peak-to-peak voltage is the voltage difference between the positive peak voltage and the negative peak voltage.

3)
Root-mean-square voltage (Vrms) is (3 / 1.414)V. We had dc before and dc voltage is constant. Now we have ac voltage which is time-varying. But it is quite troublesome to say things about this time-varying voltage. Hence, people came up with an idea. Can we derive an effective constant voltage to represent this time-varying voltage?

Yes, this is Vrms. Vrms acts like a dc voltage. Of course we know Vrms is not dc voltage.

For sinusoid voltages, Vrms is always equal to (Vpeak / 1.414). PS: 1.414 is the square root of 2.

4)
Lastly, the V. I am sure you are talking about the instantaneous voltage. This value is changing with respect to time. Given different point of time, I give you a specific value of voltage. If we still consider V= 3 sin (wt), I will say the instantaneous voltage at any time t is:

V= 3 sin (wt) (unit in volts)

I hope I can help you. Thank you

2007-02-20 00:55:52 補充：
原來是Vmean﹗剛才我誤會是V，現作以下補充

2007-02-20 00:56:04 補充：
If we still consider V= 3 sin (wt), the Vmean is 0V. You plot out the voltage waveform, you will find the NET area under curve is zero over a period of time. Hence the mean value is zero. So, if there is an non-zero area under curve of a voltage waveform, the mean voltage is not zero.

Vpeak = 0 to peak 的voltage的值
Vpeak-Vpeak = 負數那邊的peak到正數peak的voltage 的值
Vrms=root mean square voltage
Vmeans=mean of voltage