# A little help on Sine Waves.

Discussion in 'Electronics Homework Help' started by kevin haggins, Jun 23, 2016.

1. ### kevin haggins

6
0
Jun 23, 2016
I have 2 questions on sinewaves.

1. What is the voltage of a sinewave at 36 degrees, if the peak voltage is 100Volts?

2. If the VPP is 128v, what is the voltage Rms?

2. ### Kabelsalat

156
29
Jul 5, 2011
1. Find a long straight fence. Mark a starting point, and find a place in the landscape that is 36 degree to the fence. Get a rope, make sure it is exactly 100 metres (or whatever unit you choose) long tied between your body and the fence. Then walk out the distance of 100 metres (the rope will stop you) at 36 degrees angle.
Now untie the rope, and measure the shortest possible distance to the fence. There is your number.

2. Get your rope once again. Mark the starting point. Walk 128 metres in a straight line (you can use the fence if you want). Then turn exactly 90 degrees (direction doesn't matter, but rather from the fence than climbing over it just for practical purposes). Then walk 128 metres in straight line.
Now, you can measure the distance from where you standing to the starting point. There is your number.

Last edited by a moderator: Jun 24, 2016
Arouse1973, Harald Kapp and Bluejets like this.
3. ### Harald KappModeratorModerator

11,413
2,619
Nov 17, 2011
Looks like homework to me, so I moved the thread. Plus we will not answer the questions completely, we'll help you find the answer by your own so you'll be able to solve such assignments by your own in the future.

1. What is the equation describing a sinewave of frequency f and amplitude (aka peak voltage) as a function over time? Note that frequency is commonly described as number of cycles per second but can also be interpreted as a description of the change in angle over time (2*PI or 360 ° equaling one cycle). Look at the equation: where would you insert the angle (note: the value of the frequency is irrelevant).
2. How do you calculate RMS from a sine with known amplitude?
Note that in question 1 you use peak voltage Vp whereas in question 2 you refer to Vpp which is peak-to-peak voltage. The two are not the same but each can be computed from the other.

4. ### Harald KappModeratorModerator

11,413
2,619
Nov 17, 2011
That should be 64 m, shouldn't it? 128 m is peak-to-peak.

5. ### Herschel Peeler

401
65
Feb 21, 2016
Trig tables??? Find the Sine of 36 degrees, then times100 V.
Calculator???
SIN(36)*100
Do you have Microsoft Excel? It does trig functions. I suppose most other spreadsheets do, also.
Do you have a Windows computer? It has a built-in scientific calculator. "View", "scientific", "degrees", 36, "SIN", x 100

What part of VPP and RMS do you not understand?

Last edited: Jun 24, 2016
6. ### Kabelsalat

156
29
Jul 5, 2011
Yes - I was misthinking of course (why is this "oops" smiley such a cute icon???)

7. ### kevin haggins

6
0
Jun 23, 2016
Thank you for your help, i know this isnt a forum to give out answers. But im new to the electronic world.

Last edited: Jun 26, 2016

6
0
Jun 23, 2016

9. ### kevin haggins

6
0
Jun 23, 2016
I wasnt sure of the right formula, and the spread sheet is very helpfull thank you.