Doubts in double slit experiment

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Discussion Overview

The discussion revolves around the double slit experiment, specifically addressing the nature of constructive interference, the brightness of the central maxima compared to other fringes, and the underlying reasons for variations in brightness among the bright fringes. The scope includes conceptual clarifications and technical explanations related to wave interference and diffraction patterns.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question why the central maxima is the brightest spot despite the amplitude being the same for light passing through both slits.
  • One participant suggests that the amplitudes of the waves that constructively interfere differ at various orders of interference (n).
  • Another participant seeks a detailed explanation for the change in amplitude and the reason for the brightness of the central fringe compared to others.
  • A participant explains that the intensity at a point on the screen is inversely proportional to its distance from the light source, implying that the central position is closer to the sources.
  • One participant asserts that the diffraction pattern results from a convolution of the sinc² single-slit pattern and cos² fringes, noting that the finite width of the slits affects the number of visible peaks.
  • Another participant challenges the idea that slits act as point sources, stating they have a sinc² emittance profile and linking the brightness of the central fringe to the Huygens-Fresnel principle.

Areas of Agreement / Disagreement

Participants express differing views on the reasons for the brightness of the central maxima and the nature of the slits as light sources. The discussion remains unresolved, with multiple competing explanations presented.

Contextual Notes

The discussion includes assumptions about wave behavior and the effects of slit width on diffraction patterns, which are not fully explored or agreed upon by participants.

journeytospace
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hi all...it is said that constructive interference happens when the path difference is nlambda and i think wavelength,frequency and amplitude of light going through both slits is the same then
why is the central maxima is the brightest spot?
why the brightness decreases when n increases?

Since the amplitude is same why there is difference in the brightness of the bright fringes?
 
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Because the amplitudes of the waves that constructively interfere are different at 'different n'.
 
why does the amplitude changes and why the central fringe is the brightest one(why not other fringes)..can u explain in detail about it?..
 
Each of the slits acts as a radial light source (in the right half of the plane). You can think of it like this: Lines of equal field intensity are semi-circles. The intensity at a point on the circle is inversely proportional to its size, or in other words its distance from the point source. Now if you draw the screen, the screen's center is on a smaller circle (drawn around the source) than a point further away is.
 
journeytospace said:
hi all...it is said that constructive interference happens when the path difference is nlambda and i think wavelength,frequency and amplitude of light going through both slits is the same then
why is the central maxima is the brightest spot?
why the brightness decreases when n increases?

Since the amplitude is same why there is difference in the brightness of the bright fringes?

This has nothing to do with quantum mechanics. I'm moving it out of there.

Zz.
 
The diffraction pattern of a double-slit is a actually a convolution between the characteristic sinc^2 single-slit pattern that has a bright central peak and secondary peaks at either side of the central peak, and the characteristic cos^2 fringes.

The finite number of visible peaks comes about because of the finite width of the slits. As one reduces the width of the slits, the diffraction pattern will approach the ideal cos^2 case.

trinitron said:
Each of the slits acts as a radial light source (in the right half of the plane).
This is wrong, slits don't act like point sources, they have a characteristic sinc^2 emittance profile. The reason the brightest fringe is in the centre is for the same reason single-slit diffraction has a bright central peak - it all boils down to the Huygens-Fresnel principle of secondary wavelets.

Claude.
 
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