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

• guest948
In summary, there is a constructive interference pattern along the central line, as the two path lengths are the same and in phase. However, the detector only measures the time-averaged intensity, which results in the intensity increasing and decreasing as it is moved away from the slits.
guest948
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?

#### Attachments

• help!.png
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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?

guest948

## 1. What is an interference pattern?

An interference pattern is a phenomenon that occurs when two or more waves overlap and interact with each other. This interaction can result in constructive or destructive interference, leading to a pattern of alternating bright and dark regions.

## 2. How is an interference pattern created?

An interference pattern is created when two coherent sources of waves, such as light or sound, are directed towards the same point in space. The waves from each source interfere with each other, resulting in a pattern of alternating bright and dark regions.

## 3. What is the difference between constructive and destructive interference?

Constructive interference occurs when the peaks of two waves overlap, resulting in a larger amplitude and a brighter region in the interference pattern. Destructive interference occurs when the peaks of one wave overlap with the troughs of another wave, resulting in a cancellation of the waves and a darker region in the interference pattern.

## 4. What is the significance of interference patterns in science?

Interference patterns are important in many areas of science, including optics, acoustics, and quantum mechanics. They provide evidence for the wave nature of light and other types of waves, and can be used to study the properties of waves and the materials they interact with.

## 5. Can interference patterns be observed in everyday life?

Yes, interference patterns can be observed in many everyday situations. For example, when light passes through a thin film of oil on water, an interference pattern can be seen due to the different thicknesses of the film. Interference patterns can also be observed in soap bubbles, CDs, and other objects that reflect or transmit light.

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