Himanshu posted an Question
May 08, 2020 • 03:03 am 30 points
  • IIT JAM
  • Physics (PH)

Optics theory

can you derive the meaning of underline part that if they are constant means value is not changing then how they are not same???

3 Answer(s) Answer Now
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  • comment-profile-img>
    Ruby negi

    so hope you will get to know the difference between same phase and constant phase. coherent waves have constant phase difference not same phase.

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    Abhishek singh

    assume two waves, sin(wt) and sin(wt+c), where 'c' is constant. here the two waves have same frequency (w) and their phase difference is (wt+c - wt = c) constant. I guess the point of confusion here is the last line (more precisely the last word) in your uploaded pic. it is incomplete. the last word should bhi "phase difference", instead of "phase". Best regards.

  • comment-profile-img>
    Ruby negi best-answer

    When the two quantities have the same frequency, and their maximum and minimum point achieve at the same point, then the quantities are said to have in the same phase. while phase angle is the argument of sine and cosine function if the wave is sinusoidal or power of exponential for plane wave so constant phase difference means constant phase difference means if you subtract the phase angle of two waves then you will get constant value.. two wave sources are perfectly coherent if they have a constant phase difference and the same frequency, and the same waveform. 

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    Somnath Best Answer

    Suppose A and B are two sources of light. If two sources are in same phase then phase difference between them is zero. To be the coherent source condition is the difference in phase of the two source is always same.That means phase of A - phase of B should have always same value. For analogy suppose you have 10 rupees and your friend has 15 rupees. So difference of money is 5.After a month you have 25 rupees and your friend has 30 rupees.Now the difference is also 5.Which means difference is constant.But you and your friend does not have the same value of money. I think now you have understand the difference between same phase and constant phase.

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    Dhairya sharma best-answer

    like sin and cosine waves are suoerposing thay have phase difference as we know if their phase doesn't chamge with time they are coherent.but perfe coherence hard tk find so we take one source to generate them.

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    Dhairya sharma

    and dear it's defination or say property of coherent beams.

    cropped4616370841238629897.jpg
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    Dhairya sharma

    yes dear coherent means like 2 have phase difference at pi then with respect to time if they remain at same phase they are called coherent. coherent means phase difference will not chanz as time evolve.

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