In the 1st diagram of wave, what is the phase diff btw pt C and D or the phase diff btwn pt H and J? how do we measure if the phase diff is 40, 50 or 70 degrees? thank you.

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You need to know he exact location of the point to calculate that. Phase difference between two points can be calculated by dividing the distance between two points by the wavelength. Then multiply the result with 360 to find the phase in degrees or with 2Pi (2 times Pi) to find it in radians.