Huygens principle difraction

In summary, the size of the slit in a diffraction experiment should be comparable to the wavelength of the waves passing through it in order to observe diffraction. This is due to the fact that waves are truncated or "cut-off" at the slit, causing the wavefront to become bent and spread out. Huygens' principle can be used to explain this phenomenon, but it only applies to propagating waves and does not predict the existence of evanescent waves.
  • #1
C_Ovidiu
23
0
Can someone please explain this ?
Let's say u have a slit through which waves have to pass .
In order to have a difraction why does the slit have to be comparable with the wavelenghth ? It states this in every book and says that it's demonstrable using Huygens principle . I know Huygens principle but I can't see why should there be a difraction at all , the front wave being parallel with the slit all the time .
Help:frown:
 
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  • #2
The slit does not have to be comparable to wavelength, in fact, there does not even need to be a slit! The thing that causes waves to diffract is the fact that they are truncated or "cut-off" at some point. For an infinite plane wave, all the Huygens' wavelets sum to give an infinite planar wavefront, however if we truncate the wave using a slit or by some other method, the Huygen's wavelets around where the wavefront has been "cut-off" no longer sum to give a plane wave, the wavefront becomes bent, which we interpret as the wave spreading out as it propagates.

In a diffraction experiment, the slit is recommended to be around the size of the wavelength of light you are using because these are the best conditions for diffraction to be observed.

Claude.
 
  • #3
Not an answer but 1 more question.
The Huygens'algorithm is previous to Maxwell equations. Can this algorithm be infered from the Maxwell equations ?
 
  • #4
Huygens' principle can be inferred from the wave equation from field continuity arguments, however Huygens' principle is only applicable to propagating waves and does not predict the existence of evanescent waves.

Claude.
 
  • #5
C_Ovidiu said:
Can someone please explain this ?
Let's say u have a slit through which waves have to pass .
In order to have a difraction why does the slit have to be comparable with the wavelenghth ? It states this in every book and says that it's demonstrable using Huygens principle . I know Huygens principle but I can't see why should there be a difraction at all , the front wave being parallel with the slit all the time .
Help:frown:

Your first diffraction minimum will be located at an angle [tex]\theta[/tex] where
[tex]
d\sin(\theta)=\lambda
[/tex]
where d is the slit size and lambda is the wavelength. Since sine is never bigger than one, if d is less than lambda the condition can never be fulfilled. (the extreme case of this is when d is very much smaller than lambda in which case the wavefronts coming out look sphereical and obviously can't interfere with each other).

On the other hand if d is very very big, then very many diffraction minima (and maxima) will occur within a very small angle and will not be easy to see. (the extreme case of this is when d is very much larger than lambda in which case there is no screen at all, it's "all slit").

so, you need d to be bigger than, but comparable to, the wavelength.

Cheers.
 

What is Huygens principle diffraction?

Huygens principle diffraction is a theory in physics that explains the behavior of waves when they encounter obstacles or pass through small openings. It states that every point on a wavefront can be considered as a source of secondary wavelets, which spread out in all directions and interfere with each other to produce a diffraction pattern.

What is the significance of Huygens principle diffraction?

Huygens principle diffraction is significant because it helps us understand how waves propagate and interact with objects in their path. It is also useful in various applications, such as in optics for understanding the behavior of light, and in seismology for studying earthquake waves.

How does Huygens principle diffraction differ from other theories of diffraction?

Huygens principle diffraction differs from other theories, such as the Fraunhofer diffraction theory, in that it considers the wave nature of light and does not require the assumption of a plane wave. It also takes into account the secondary wavelets created at each point of the wavefront, rather than treating the wave as a whole.

What factors affect the diffraction pattern according to Huygens principle?

The size of the diffracting object, the wavelength of the wave, and the distance between the object and the screen on which the pattern is observed are all factors that affect the diffraction pattern according to Huygens principle. The shape and material of the object can also play a role.

How is Huygens principle diffraction applied in real-world situations?

Huygens principle diffraction is applied in various fields, such as in the design of antennas, lenses, and other optical components. It is also used in the study of sound waves and seismic waves, and in the development of diffraction-based imaging techniques, such as holography.

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