# A source's effect on diffraction pattern

• Aldnoahz
In summary, when a source moves away or towards a slit in a single-slit diffraction pattern, the intensity of the diffraction pattern is affected but the fringe width remains constant. This is due to the relationship between the path difference of the secondary wavelets and the intensity of the illumination of the slit. When the source moves away, the intensity decreases and when it moves towards, the intensity increases. However, the fringe width does not change. Similarly, when the source moves sideways, the intensity is affected but the fringe width remains the same. This phenomenon can be explained by the path difference principle in diffraction.
Aldnoahz
I am quite aware of the effect of slit width and wavelength in a single-slit diffraction pattern. However, my teacher has never touched on the effect of a source moving towards or away from the slit. Neither can I find any satisfactory or comprehensible response to this phenomenon. While my intuition tells me that only the intensity changes, I am not entirely sure..

Could anybody discuss the effect on the diffraction pattern when a source moves away, towards, or sideways with respect to the slit? What about the effect of distance between the slit and the screen on which the wave is incident (will the diffraction pattern become wider with less intensity)?

Any explanation will be appreciated. Thanks!

Aldnoahz said:
While my intuition tells me that only the intensity changes, I am not entirely sure..

In the diffraction pattern the intensity is affected by the path difference /relationship between various secondary wavelets arriving at a point on the screen - and the maxima and minima intensity is related to the intensity of illumination of the slit/hole so if someone displaces the source away/near/sideways from the slit - the illumination of the slit gets affected and the fringe width should not change.

drvrm said:
In the diffraction pattern the intensity is affected by the path difference /relationship between various secondary wavelets arriving at a point on the screen - and the maxima and minima intensity is related to the intensity of illumination of the slit/hole so if someone displaces the source away/near/sideways from the slit - the illumination of the slit gets affected and the fringe width should not change.

Thanks for replying. Just to clear things up, as the source moves away from the slit (no matter the direction), only intensity is affected, which decreases, and vice versa?

## 1. How does the distance between a source and a diffraction pattern affect the pattern itself?

As the distance between a source and a diffraction pattern increases, the pattern becomes more spread out and less defined. This is because the waves from the source have more space to interact with each other and form interference patterns.

## 2. Can the size of a source affect the diffraction pattern?

Yes, the size of a source does have an effect on the diffraction pattern. A smaller source will produce a diffraction pattern with narrower fringes and a larger source will produce a pattern with wider fringes.

## 3. How does the wavelength of the source's waves impact the diffraction pattern?

The wavelength of a source's waves has a direct effect on the spacing of the fringes in a diffraction pattern. A shorter wavelength will result in narrower fringes, while a longer wavelength will result in wider fringes.

## 4. Does the shape of the source affect the diffraction pattern?

Yes, the shape of a source can have an impact on the diffraction pattern. A point source, such as a single slit, will produce a diffraction pattern with a central bright spot and smaller, fainter fringes on either side. A larger, extended source, such as a double slit, will produce a more complex pattern with multiple bright spots and fringes.

## 5. Can the medium through which the waves travel affect the diffraction pattern?

Yes, the medium through which waves travel can have an influence on the diffraction pattern. Different media have different refractive indices, which can affect the direction and intensity of the waves as they pass through, ultimately altering the resulting diffraction pattern.

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