Diffraction - Why must slit width be comparable to the wavelength of light?

In summary, diffraction occurs when the slit width is comparable to the wavelength of the light being shone on it. This is because the electromagnetic field is attenuated by the slit material, preventing it from being represented as a perfect plane wave. If the slit is much larger than the wavelength, diffraction is not noticeable, but when the slit is comparable to the wavelength, the wave inside the slit is disrupted, causing diffraction to occur. This is due to constricting boundary conditions that prevent the wave from being planar.
  • #1
nousername
31
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Hey guys,

In diffraction of light, why must the slit width be of comparable size to the wavelength of the light being shone on it for diffraction to be noticed most?

Thanks
 
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  • #2
The longer the wavelength, the closer the slit has to be away and vice-verca. As it has more energy it just makes it easier to notice the difractiong
 
  • #3
Diffraction happens because the electromagnetic fields must satisfy the wave equation.
The electromagnetic field is attenuated by the material of the slit, therefore the electromagnetic field cannot be represented as a perfect plane wave when it goes through the slit. (A perfect plane wave requires a large amount of free space).
If the slit width is much larger than the light's wavelength, the amplitude of the field drops off after many wavelengths to the side, so in the middle of the slit, the wave is mostly planar. (I.e. diffraction doesn't happen much).
If the slit is comparable to the wavelength, the wave cannot be planar within the slit, because the amplitude must drop off only a wavelength to the side, so the planar quality of the wave is messed up.
So basically, it is because of constricting boundary conditions that the wave inside the slit can't be planar (if the slit size is comparable to the wavelength), which causes diffraction.
 
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FAQ: Diffraction - Why must slit width be comparable to the wavelength of light?

1. How does the slit width affect diffraction?

The slit width directly affects the amount of diffraction that occurs. When the slit width is comparable to the wavelength of light, the diffracted waves from each edge of the slit overlap and create a distinct diffraction pattern. If the slit width is too large, the diffraction pattern will be less defined, and if it is too small, there may be no diffraction at all.

2. Why is the slit width compared to the wavelength of light instead of just being a fixed size?

The wavelength of light is used as a reference because it determines the size of the diffracted waves. When the slit width is comparable to the wavelength of light, the diffracted waves will have a significant overlap, creating a clear and distinct diffraction pattern. If the slit width is fixed, the diffraction pattern will vary depending on the wavelength of light being used.

3. Can diffraction occur if the slit width is not comparable to the wavelength of light?

Yes, diffraction can occur even if the slit width is not comparable to the wavelength of light. However, the resulting diffraction pattern will be less defined and may not be easily observed. This is because the diffracted waves from each edge of the slit will not overlap as much, leading to a less distinctive pattern.

4. Is there an optimal slit width for diffraction?

There is no specific optimal slit width for diffraction, as it depends on the specific experimental setup and the desired outcome. Generally, the slit width should be comparable to the wavelength of light being used to achieve a clear and defined diffraction pattern. However, for certain experiments, a different slit width may be more suitable.

5. How does the wavelength of light affect diffraction?

The wavelength of light directly affects the amount of diffraction that occurs. When the wavelength of light is longer, the diffracted waves will spread out more, resulting in a larger diffraction pattern. Conversely, when the wavelength of light is shorter, the diffracted waves will be more concentrated, resulting in a smaller diffraction pattern.

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