Why does the intensity vary when the detector is moved away from the slits?

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SUMMARY

The discussion centers on the variation of intensity measured by a detector as it is moved away from slits in a double-slit interference experiment. Participants confirm that constructive interference occurs when the path lengths from the source to the detector are equal, resulting in a consistent phase relationship. However, the intensity fluctuates due to the detector's inability to measure instantaneous energy, instead capturing a time-averaged intensity of the radiation. This leads to the conclusion that the intensity varies with distance due to the spatial distribution of the interference pattern.

PREREQUISITES
  • Understanding of double-slit interference
  • Knowledge of constructive and destructive interference
  • Familiarity with phase relationships in wave mechanics
  • Basic principles of detector response in wave measurements
NEXT STEPS
  • Research the mathematical formulation of double-slit interference patterns
  • Explore the concept of phase difference in wave mechanics
  • Learn about the response time of different types of detectors in wave measurements
  • Investigate the effects of distance on wave intensity and interference patterns
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Physics students, educators, and researchers interested in wave mechanics, particularly those studying interference patterns and detector behavior in experimental setups.

guest948
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Homework Statement
A student directs a beam of microwaves ... (Please refer to the attachment.)
Relevant Equations
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I guess C: constructive interference pattern along the central line.

Am I correct?
 

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guest948 said:
C: constructive interference pattern along the central line.
If the two paths (through each slit) add constructively, as you guessed, then why would the intensity measured increase and decrease with distance as shown in drawing C?

What do you know about the two path lengths from the source to the detector? What does that mean for the phase relationship between them?
 
DaveE said:
then why would the intensity measured increase and decrease with distance as shown in drawing C?
The path lengths are the same, so they are in phase and they add constructively along PQ.
So the answer is C (or A)?
 
guest948 said:
The path lengths are the same, so they are in phase and they add constructively along PQ.
So the answer is C (or A)?
The detector can't respond fast enough to measure the instantaneous energy in the radio wave, it only measures the time averaged intensity of the radiation. So why then would the intensity increase and decrease as the detector is moved away from the slits?
 
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