# Quick instantaneous sin value question

Discussion in 'Homework Help' started by markp912, Mar 6, 2009.

1. ### markp912 Thread Starter Member

Feb 4, 2009
14
0
Q: A certain sin wave has a positive going zero crossing at 0° and an rms value of 20V. Calculate its instantaneous value at each of the following angles: (a)15° (b)33° (c)325°

So my Vp=28.28
But since my starting point is at 0° would that mean each of those angles are lagging and i would have to use the formula: y=Vp sin(θ-Φ)?

Or would i just use y=Vpsinθ

Thank you.

2. ### RiJoRI Well-Known Member

Aug 15, 2007
536
29
WHY are they lagging? Lagging in regard to what? And why couldn't you return the values as RMS?

Methinks thou art working too hard!

--Rich

3. ### markp912 Thread Starter Member

Feb 4, 2009
14
0
lagging b/c the new angle is at 30° now?

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
293
Your minimum voltage is at 0 deg, and the maximum is at 90 deg. Why worry about lead/lag?

5. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
674
RMS has no meaning for instantaneous voltage readings.

6. ### markp912 Thread Starter Member

Feb 4, 2009
14
0
Wouldnt the 325° angle lag b its so far out from 0°?

7. ### Ron H AAC Fanatic!

Apr 14, 2005
7,049
674
Would a picture help?

File size:
13.8 KB
Views:
48
8. ### markp912 Thread Starter Member

Feb 4, 2009
14
0
WOW! that picture did help a lot. i feel like an idiot now. there is only one sine wave going. thanks for all of your help guys.