# RMS values

Discussion in 'Homework Help' started by DysonElec, Apr 21, 2008.

1. ### DysonElec Thread Starter New Member

Apr 21, 2008
5
0
Hi, I have an exam coming up and I need a little help with getting my head around "RMS values". There was a question in a mock exam I did which was "what is the 'constant' for RMS values?" now I know that the answer is 0.707 but I don't understand what it's about. Can anyone point me in the right direction plzz? thanks

2. ### mik3 Senior Member

Feb 4, 2008
4,846
67
To find the rms value you multiply the peak value by the constant you said (0.707) which is more accurately equal to 1 divided by square root of 2. Also this constant is valid only for pure sine waves and for other type of signals like triangular waves. This constant is derived by using calculus. Are you interested to see how?

3. ### DysonElec Thread Starter New Member

Apr 21, 2008
5
0
Yes very! but have you got all week? lol

4. ### mik3 Senior Member

Feb 4, 2008
4,846
67
Check this website buddy. I think you will study all the week to understand!!!!

http://www.dataforth.com/catalog/pdf/an101.pdf

Its boring to write down all these explanation , its hard to calculate it but......if you dont understand the website i will try to explain you.

5. ### DysonElec Thread Starter New Member

Apr 21, 2008
5
0
I greatly appreciate your help, but i already checked this website out, and couldn't understand it. the coarse i have just started is electrical installation, so only a basic understanding is needed. could you please find a why to help me understand the basics of this topic? thanks

6. ### mik3 Senior Member

Feb 4, 2008
4,846
67
Come on dont be bored, read it carefully. You actually dont need to know how this constant is derived, just use it. I dont have time now to explain maybe another time i will post the explanation.

7. ### DysonElec Thread Starter New Member

Apr 21, 2008
5
0
ok i will have a try thanks anyway

8. ### Dave Retired Moderator

Nov 17, 2003
6,960
162
If only a basic understanding is needed then accept that the 0.707 comes from $1/$$\sqrt{2}$ and then read the qualitative description in the e-book: http://www.allaboutcircuits.com/vol_2/chpt_1/3.html

Dave

9. ### DysonElec Thread Starter New Member

Apr 21, 2008
5
0
very helpful! thank you very much

10. ### Dave Retired Moderator

Nov 17, 2003
6,960
162
No problem

If you also do a search for the term RMS from the main AAC page you will find many other discussions on RMS here in the forums and other uses in the e-book.

Dave