# Homework Help: Phase,phase shift ,sine curve

1. Jan 16, 2009

### Rola

What is the meaning of phase and phase shift??

and How can I obtain phase shift from the sine curve ??

http://www12.0zz0.com/2009/01/16/17/965512159.jpg [Broken]

Note : I'm a begginer in physics , so please if you can , please explain the concept in details ..

Thank you ..

Last edited by a moderator: May 3, 2017
2. Jan 16, 2009

### Staff: Mentor

Thread moved to Homework Help. Welcome to the PF, Rola. Phase shift is how much that curve is shifted left or right of a zero-phase position.

The curve you're drawn is a cosine curve, since it is at max positive amplitude when the argument is zero. If you shift that drawing to the right by 1/8 of a wavelength, you would have a sin() curve. If you plot sin() and cos() on the same graph, you will see that the phase of the two is different (sifted) by PI/4.

3. Jan 16, 2009

### Delphi51

You can explore this on a graphing calculator.
Graph y = sin(x)
Then graph y = sin(x - 30) in degree mode. If using radians, replace 30 with pi/6.
You should see a 30 degree shift to the right. Play around with other negative and positive numbers until you have the feel of it.

4. Jan 16, 2009

### Rola

I understand the concept of phase shift..

but in this graph how can I know the zero-phase position??

5. Jan 16, 2009

### Staff: Mentor

I'd assumed that your sin(0) was the "zero phase". If that is a plot of a cos() function, then there is a phase shift in the function cos(theta - phase).

Phase is relative to the generating function. What equation did you use to plot your graph?

6. Jan 16, 2009

### Rola

Do you mean that you make comparison between standard sine curve and the graph ..

because in my book they write

phase shift =1/4*2pi=pi/2

but I dont know why they make this ..

I attached the file that contain the question ..

and if you can can tell me if mu solution to the question in red color true

#### Attached Files:

• ###### 123.doc
File size:
55 KB
Views:
93
7. Jan 16, 2009

### Delphi51

I can't see the Word document you attached yet.
In the graph in the first post, 360 degrees or 2 pi radians is the width of one complete oscillation - from 0 to 12.5 where the dashed vertical line is located. So the question you must ask is: how far has it been shifted to the right? The basic sin() curve begins at the origin (height zero) and goes up from there. That place has been shifted to the right about 9 of the units on the horizontal axis. In degrees, it is shifted about 9/12.5 or 3/4 of 360 degrees. The phase shift is normally expressed as an angle regardless of what units you have on the x axis.

8. Jan 16, 2009

### Staff: Mentor

I approved the attachment.

In the attachment, be careful in your frequency calculation -- you are right that the period is 12.5 hours, but the units of 1/T are not seconds unless you do a conversion....

I only skimmed the rest, but it looks like you are on the right track.

Delphi -- could you please check it now? Thanks.

9. Jan 16, 2009

### Delphi51

Yes, it all looks good except for that one place where you must convert the period into seconds before computing the frequency in Hertz. In the good old days, we used "cycles per second" instead of Hertz!

10. Jan 23, 2009

### Rola

Thank you very much for helping me..