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# Physics past papers question

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1. Two coherent sources emit waves of wavelengths lamda in phase. At a point where the two wavaes smeet they have aphase difference of 90 degrees . Which of he following could be the path difference?
A 2lamda
B lamda
c lamda /2
D lamda/4
2. (Original post by Rosie1999)
Two coherent sources emit waves of wavelengths lamda in phase. At a point where the two wavaes smeet they have aphase difference of 90 degrees . Which of he following could be the path difference?
A 2lamda
B lamda
c lamda /2
D lamda/4
Path difference is the difference in distance traveled by the two waves from their sources to a given point on the pattern. In order to get a phase difference of 90 degrees, you need to start one wave from lambda/4 behind the other.
Another way to think of it for coherent waves is to say that lambda = 360 degrees, so lambda/2 = 180 degrees and lambda/4 = 90 degrees.
3. (Original post by Laurasaur)
Path difference is the difference in distance traveled by the two waves from their sources to a given point on the pattern. In order to get a phase difference of 90 degrees, you need to start one wave from lambda/4 behind the other.
Another way to think of it for coherent waves is to say that lambda = 360 degrees, so lambda/2 = 180 degrees and lambda/4 = 90 degrees.
how do you know lambda is equal to 360?
Thanks for your expalnation tho and graoh so much better. and do you have sheets for revision ? or notes for that lesson ?
4. (Original post by Rosie1999)
how do you know lambda is equal to 360?
Thanks for your expalnation tho and graoh so much better. and do you have sheets for revision ? or notes for that lesson ?
lamda/ 1 complete wavelength is when a particle on a wave completes a whole oscillation. In other words the particle moves through 360deg
5. (Original post by Rosie1999)
how do you know lambda is equal to 360?
Thanks for your expalnation tho and graoh so much better. and do you have sheets for revision ? or notes for that lesson ?
Did you learn about sine waves in gcse maths? Basically, 1 complete oscillation is 360 degrees (also 2 pi radians), like completing a circle. It's just something you'll have to remember

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