What is the Distance Between Two Points with a Phase Difference of 45 Degrees?

In summary, the problem asks for the wavelength of a function given the wavenumber, and the solution suggests that the wavelength is equal to 2pi/7.5. The distance between points with a phase difference of 45 degrees is 1/8 of a wavelength.
  • #1
Lavabug
866
37

Homework Statement


For the given wave on a string:
y = 0.001 cos (7.5x + 15t)

find the distance between two points which have a phase difference of 45 degrees at the same instant in time.


The Attempt at a Solution


No idea how to solve this. Please help.
 
Physics news on Phys.org
  • #2
Lavabug said:

Homework Statement


For the given wave on a string:
y = 0.001 cos (7.5x + 15t)

find the distance between two points which have a phase difference of 45 degrees at the same instant in time.


The Attempt at a Solution


No idea how to solve this. Please help.

What is the wavelength of that function?
 
  • #3
I think I'm on to something:

The phase between the start and the end of a full wavelength is 2pi (full cycle).
For half a wavelength that's pi
For a quarter wavelength that's pi/2 or 90 degrees, ie: the phase between maxes and mins.
For an 1/8 of a wavelength the phase is pi/4, or 45 degrees.

The problem gives me the wavenumber so I can find the wavelength: 2pi/7.5 = lambda

So I think I can draw the following similarity:

lambda is to 2pi as
lambda/8 is to pi/4 ?

So the distance between points that represent a phase of 45 degrees is 1/8 of a wavelength?
 
  • #4
Lavabug said:
I think I'm on to something:

The phase between the start and the end of a full wavelength is 2pi (full cycle).
For half a wavelength that's pi
For a quarter wavelength that's pi/2 or 90 degrees, ie: the phase between maxes and mins.
For an 1/8 of a wavelength the phase is pi/4, or 45 degrees.

The problem gives me the wavenumber so I can find the wavelength: 2pi/7.5 = lambda

So I think I can draw the following similarity:

lambda is to 2pi as
lambda/8 is to pi/4 ?

So the distance between points that represent a phase of 45 degrees is 1/8 of a wavelength?

Looks good so far. Now what is the length of a wavelength for the equation that you are given. Assume mks units, even though they are not stating them explicitly...
 
  • #5
Or I suppose it could be cgs units. Do they show units in any other similar problems?
 
  • #6
I'm pretty sure the units are just SI. I got my wavelength from the given wavenumber(7.5): lambda = 2pi/7.5 (don't have a calculator on hand lol).

The distance between points with 45 degree would be an eighth of that quantity.

So my idea is correct?
 
  • #7
Lavabug said:
I'm pretty sure the units are just SI. I got my wavelength from the given wavenumber(7.5): lambda = 2pi/7.5 (don't have a calculator on hand lol).

The distance between points with 45 degree would be an eighth of that quantity.

So my idea is correct?

Seems like the correct approach.

You could also graph the function either with a graphing calculator or just Excel, to have a sanity check on your answer...
 
  • #8
How would I graph it? Can I exclude the time dependency (angfreq*t) and just plot .001cos(kx)?
 
  • #9
Lavabug said:
How would I graph it? Can I exclude the time dependency (angfreq*t) and just plot .001cos(kx)?

Yes, the problem says "at the same instant in time", so you can set t=0 arbitrarily.
 
  • #10
I tried plotting it with an interval from 0 to half of my given wavelength(pi/7.5) and got this:

http://www.wolframalpha.com/input/?i=.001cos(7.5x)++x+from+0+to+pi/7.5

Which shows a 180 degree phase difference

Plotting half that interval (pi/15) shows a 90 degree phase difference:
http://www.wolframalpha.com/input/?i=.001cos(7.5x)++x+from+0+to+pi/15

aaand with half of that I've got (pi/30), which looks like:
http://www.wolframalpha.com/input/?i=.001cos(7.5x)++x+from+0+to+pi/30

I'm fairly convinced that pi/30 is the distance I'm looking for. Thanks!
 

What is the phase problem in waves?

The phase problem in waves refers to the difficulty in accurately determining the phase of a wave. Phase is a measure of the position of a wave in its cycle, and it is crucial in understanding the behavior and interactions of waves. However, it is often challenging to measure or calculate the exact phase of a wave, which can lead to inaccuracies in predicting its behavior.

How does the phase of a wave affect its properties?

The phase of a wave plays a significant role in determining its properties. For example, waves that are in phase (with the same phase angle) can combine constructively, resulting in a larger amplitude. On the other hand, waves that are out of phase (with opposite phase angles) can cancel each other out, resulting in a smaller amplitude. The phase also affects the interference patterns of waves, which can be observed in phenomena such as diffraction and beats.

What causes the phase problem in waves?

The phase problem in waves can arise due to various factors, including inconsistencies in measurement or calculation methods, variations in wave properties such as frequency and wavelength, and interference from other waves. It can also be caused by the limitations of instruments used to measure waves, which may not be able to accurately capture the phase information.

How is the phase problem addressed in different fields of science?

The phase problem is addressed differently in various fields of science, depending on the type of waves being studied and the methods used to measure them. In some cases, advanced mathematical models and algorithms are used to calculate the phase of waves. In other cases, techniques such as signal processing and interference analysis are employed to determine the phase of waves.

What are some applications of understanding the phase problem in waves?

Understanding the phase problem in waves is essential for many practical applications, including communication systems, medical imaging, and materials testing. By accurately measuring and controlling the phase of waves, we can improve the efficiency and reliability of these systems. Additionally, understanding the phase of waves can also help us gain insights into the fundamental properties of matter and the behavior of natural phenomena, such as earthquake waves and ocean currents.

Similar threads

  • Introductory Physics Homework Help
Replies
21
Views
260
  • Introductory Physics Homework Help
Replies
12
Views
258
  • Introductory Physics Homework Help
Replies
6
Views
203
  • Introductory Physics Homework Help
Replies
4
Views
3K
  • Introductory Physics Homework Help
Replies
15
Views
2K
  • Introductory Physics Homework Help
Replies
7
Views
2K
  • Introductory Physics Homework Help
Replies
29
Views
1K
  • Introductory Physics Homework Help
Replies
8
Views
2K
  • Introductory Physics Homework Help
Replies
5
Views
876
  • Introductory Physics Homework Help
Replies
20
Views
2K
Back
Top