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

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Homework Help Overview

The discussion revolves around the phenomenon of intensity variation in a wave interference pattern as a detector is moved away from slits, likely in the context of wave optics. Participants are exploring the implications of constructive interference and the relationship between path lengths and intensity measurements.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the relationship between path lengths and phase relationships, particularly how these affect the intensity measured by the detector. There is also exploration of the detector's response time and its effect on intensity readings.

Discussion Status

The discussion is active with participants attempting to clarify their understanding of constructive interference and its implications for intensity variation. There are multiple interpretations being explored regarding the detector's measurements and the nature of the interference pattern.

Contextual Notes

Participants are considering the limitations of the detector in measuring instantaneous energy versus time-averaged intensity, which may influence their understanding of the observed intensity variations.

guest948
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Homework Statement
A student directs a beam of microwaves ... (Please refer to the attachment.)
Relevant Equations
/
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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