Phase difference between two light waves of the same frequency

the diagram.



i found that the phase difference between them is 100º
but how is the answer 260
can someone please explain?

Since 100 is not in the list, you need to pick another. And there is a best candidate.

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

Guessing, are we?
It is not 150, you already have the correct answer as quoted in #1

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...

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

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

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

this one is for 220º

i still dont understand it... :(

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##.

If the phase difference between the first and the second is 100°, what is the phase difference between the second and first?

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.