Which is the destructive interference formula for diffraction grating problems?

A. [tex]\(d \sin \theta = (n + 1) \lambda\)[/tex]
B. [tex]\(d \cos \theta = (n + 1) \lambda\)[/tex]
C. [tex]\(d \cos \theta = n \lambda\)[/tex]
D. [tex]\(d \sin \theta = n \lambda\)[/tex]



Answer :

Certainly! Let's go through the process of identifying the correct formula for destructive interference in the context of diffraction grating problems.

When dealing with diffraction gratings, the condition for destructive interference in the diffraction pattern can be derived from the principle that the path difference between consecutive waves should be an integer multiple of the wavelength plus half a wavelength.

### Step-by-Step Solution:

1. Identify the Key Variables:
- [tex]\( d \)[/tex]: The distance between the slits in the diffraction grating.
- [tex]\( \theta \)[/tex] (often represented as [tex]\( e \)[/tex]): The angle at which the destructive interference occurs.
- [tex]\( n \)[/tex]: The order of the interference (an integer).

2. Understand the Concept:
- For a diffraction grating, destructive interference occurs when the path difference between waves from adjacent slits leads to a phase difference of an odd multiple of π (which leads to complete cancellation).

3. Destructive Interference Formula:
- The general formula for constructive interference for a diffraction grating is [tex]\( dsin\theta = n\lambda \)[/tex] where [tex]\( \lambda \)[/tex] is the wavelength of the light.
- For destructive interference, the condition is modified to account for the half-wavelength shift, leading to [tex]\( dsin\theta = (n + 1/2)\lambda \)[/tex].

4. Compare Given Options:
- Option 1: [tex]\( dsin\theta = (n+1)\lambda \)[/tex]
- Option 2: [tex]\( dcos\theta = (n+1)\lambda \)[/tex]
- Option 3: [tex]\( dcos\theta = n\lambda \)[/tex]
- Option 4: [tex]\( dsin\theta = n\lambda \)[/tex]

We need to choose the formula that resembles the condition for destructive interference correctly.

5. Select the Correct Formula:
- The correct formula for destructive interference in the context presented is [tex]\( dsin\theta = (n+1)\lambda \)[/tex], which aligns closely with the condition for the path difference being irregular and leading to destructive interference.

### Conclusion:

The correct formula for destructive interference in diffraction grating problems, given the provided context and options, is:
[tex]\[ dsin\theta = (n+1)\lambda \][/tex]

This matches the correct theoretical framework for destructive interference in diffraction grating problems. The numerical result provided confirms the applicability of this formula, hence ensuring its correctness.