# Why subsidary maximum has lower intensity physically in single-slit diffraction?

• Arup Biswas
In summary, in single slit diffraction, the subsidiary maximum has lower intensity compared to the central maximum. This can be mathematically explained through the intensity equation. However, physically, we can explain it by considering that the central and first maximum have the same activity to produce constructive interference, and the intensity drop due to the extra path traversed is negligible as they are very close. Additionally, in the first maximum, the rays interfere constructively depending on their path difference, with a phase difference of zero for the central maximum and an integral multiple of pi for other maxima.
Arup Biswas
In single slit diffraction the subsidary maximum has lower intensity than of central. Yes mathematically from the intensity equation we can see that. But how physically we can explain that? When the central and the 1st maxima has same activity to produce constructive interference( as in same phase). We neglect the intensity drop due to extra path traversed as they are very close!

Arup Biswas said:
When the central and the 1st maxima has same activity to produce constructive interference( as in same phase).
Does it?

@Ibix the rays there interfere constructively depending on their path difference. In case of central path difference is 0 so phase difference also zero. In case of other maxima due to path difference phase difference must be integral multiple of pi so they are in phase! Doesn't it??

Arup Biswas said:
the rays there
Which rays?

## 1. Why does a subsidiary maximum have lower intensity physically in single-slit diffraction?

The subsidiary maximum, also known as a secondary maximum, is a result of interference between light waves passing through a single slit. The intensity of the light at this point is lower because it is a point of destructive interference, where the peaks of one wave cancel out the troughs of another. This is in contrast to the central maximum, where constructive interference leads to a higher intensity of light.

## 2. How does the width of the slit affect the intensity of the subsidiary maximum in single-slit diffraction?

The width of the slit has a direct impact on the intensity of the subsidiary maximum. As the slit becomes narrower, the wavelength of the light becomes larger in comparison, leading to a decrease in the angle of diffraction. This results in a wider central maximum and narrower subsidiary maxima, resulting in a decrease in intensity at the subsidiary maximum.

## 3. What is the relationship between the distance from the slit and the intensity of the subsidiary maximum in single-slit diffraction?

The intensity of the subsidiary maximum decreases as the distance from the slit increases. This is because the diffraction pattern spreads out as the distance increases, resulting in a decrease in the intensity of the subsidiary maximum. In contrast, the central maximum remains constant regardless of the distance from the slit.

## 4. How does the wavelength of light affect the intensity of the subsidiary maximum in single-slit diffraction?

The intensity of the subsidiary maximum is inversely proportional to the wavelength of light. This means that as the wavelength of light increases, the distance between the central maximum and the subsidiary maximum decreases, resulting in a decrease in the intensity at the subsidiary maximum.

## 5. Can the intensity of the subsidiary maximum in single-slit diffraction be increased?

The intensity of the subsidiary maximum cannot be increased without altering the setup of the experiment. However, the intensity of the central maximum can be increased by using a narrower slit or a light source with a shorter wavelength.

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