Phase difference between two light waves of the same frequency

  • #1
hello478
42
0
Homework Statement
Two light waves of the same frequency are represented by the diagram.


What could be the phase difference between the two waves?

A 150°
B 220°
C 260°
D 330°
Relevant Equations
phase difference = phase angle in this diagram...
the diagram.

Capture.jpg


i found that the phase difference between them is 100º
but how is the answer 260
can someone please explain?
 
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  • #2
Since 100 is not in the list, you need to pick another. And there is a best candidate.
 
  • #3
BvU said:
Since 100 is not in the list, you need to pick another. And there is a best candidate.
is it 150º ? because it is the closest to 100º
 
  • #4
Guessing, are we?
It is not 150, you already have the correct answer as quoted in #1
 
  • #5
BvU said:
Guessing, are we?
It is not 150, you already have the correct answer as quoted in #1
i dont know how it came to be the answer...
 
  • #6
As a useful exercise you could draw 4 graphs, each with two waves. The first one with a phase difference of150 degrees, the others with 220, 260 and 330
 
  • #7
BvU said:
As a useful exercise you could draw 4 graphs, each with two waves. The first one with a phase difference of150 degrees, the others with 220, 260 and 330
drawing them, give me 5 mins and ill get back to you
 
  • #8
1710346517449.png

this is what i got for 260º
what next??
BvU said:
As a useful exercise you could draw 4 graphs, each with two waves. The first one with a phase difference of150 degrees, the others with 220, 260 and 330
 
Last edited:
  • #9
1710347222111.png

this one is for 220º
 
  • #10
i still dont understand it... :(
 
  • #11
hello478 said:
i still dont understand it... :(
The curves are ##\sin(\theta+\phi_1)## and ##\sin(\theta+\phi_2)##.
Suppose ##\phi_1+2\pi>\phi_2>\phi_1##. The phase difference is ##\phi_2-\phi_1##.
But ##\sin(\theta+\phi_1)=\sin(\theta+\phi_1+2\pi)##, so those are two representations of the same wave. So we could equally say the phase difference is ##\phi_1+2\pi-\phi_2##.
 
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  • #12
If the phase difference between the first and the second is 100°, what is the phase difference between the second and first?
 
  • #13
hello478 said:
i still dont understand it... :(
My two-pennies-worth…

On the Post 1# diagram, call the larger-amplitude wave ‘A’ and the smaller-amplitude wave ‘B’.

A passes through (0, 0). The next 'matching' point on B is (100º,0). So the phase difference is (100 – 0 =) 100º.

But you could equally well say:

B passes through (100º, 0). The next 'matching' point on A is (360º, 0). So the phase difference is (360-100=) 260º.

Remember that an angle of (say) +260º is the same as an angle of -100º. You can choose which wave (A or B) is the reference.
 
Last edited:
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