The correct answer is B because:

The maximum intensity of light is the region where the light is brightest due to constructive interference
The region of maximum intensity is always in the direction in which the light is incident
Additionally, maximum intensities are not limited to the region just mentioned and regions close to it, but maximum intensity can also be observed at different angles
There are different orders which are given by the diffraction grating equation is given by : $d s i n θ = n λ$
So, the angles of diffraction of the maxima are equal to $θ_{n} = s i n^{- 1} (\frac{n λ}{d})$
- When n = 0, $θ_{0} = s i n^{- 1} (0) = 0$
- When n = 1, $θ_{1} = s i n^{- 1} (\frac{λ}{d})$
- When n = 2, $θ_{2} = s i n^{- 1} (\frac{2 λ}{d})$
- When n = 3, $θ_{3} = s i n^{- 1} (\frac{3 λ}{d})$
The angle of diffraction from the 0th order maxima is smaller than the angular separation (the difference in angle of diffraction) of the 2nd order and 1st order maxima, i.e.
- $θ_{1} - θ_{0} = θ_{1} < (θ_{2} - θ_{1})$
The same is true as the order n increases, so, for small angles, the difference in angles would be the same

A is incorrect because regions of maximum intensity should be observed at different angles, the range of angles in this diagram is too small

C is incorrect because the angles of diffraction in this diagram are too large

D is incorrect because the region of maximum intensity is always in the direction in which the light is incident, meaning there must be a central arrow, which this diagram does not have

Diffraction & Interference (CIE A Level Physics)

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