A 1.6-cm-wide diffraction grating has 1000 slits. It is illuminated by light of wavelength 530 nm. What are the angles of the first two diffraction orders?

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Answer:

The answer is "[tex]1.96^{\circ} \ and \ 3.94^{\circ}[/tex]"

Explanation:

[tex]N= 1000 \frac{slit}{cm} \\\\\lambda=550 nm\ \ =550 \times 10^{-9} \ m\\\\width=1.6 \ cm[/tex]

We can find the distance between any two adjacent slits by using

[tex]\to d= \frac{1.6}{N}\\\\ \therefore\\ \to d= \frac{1.6}{1000} \ cm= 1.6 \times 10^{-5} m\\[/tex]

We know that the angle of the mth fringe is given by                  

[tex]\sin \theta_m = \frac{m\lambda}{d}\\\\ \sin \theta_1 = \frac{1\lambda}{d}\\\\\theta_1 = \sin^{-1} \frac{1\lambda}{d}\\\\\theta_1 = \sin^{-1}(\frac{1 \times 550 \times 10^{-9}}{1.6 \times 10^{-5}})\\\\ \theta_1=1.96^{\circ}\\\\[/tex]

Using the same way:  

[tex]\sin \theta_2 = \frac{2\times \lambda}{d}\\\\\theta_2 = \sin^{-1} \frac{2\times \lambda}{d}\\\\\theta_2 = \sin^{-1}(\frac{2 \times 550 \times 10^{-9}}{1.6 \times 10^{-5}})\\\\\theta_2=3.94^{\circ}\\\\[/tex]

By using the Huygens formula, the angles of the first two orders are 4 degrees and 8 degrees approximately.

Given that a 1.6cm wide diffraction grating has 1000 slits.

The slit spacing = (1.6 x [tex]10^{-2}[/tex]) / 1000

The slit spacing = 1.6 x [tex]1.6^{-5}[/tex]

Also, it is given that It is illuminated by light of wavelength 530 nm

Sin∅ = nλ/d

When n = 1

Sin∅ = 530 x [tex]10^{-9}[/tex]/1.6 x [tex]10^{-5}[/tex]

Sin∅ = 0.033125

∅ = [tex]Sin^{-1}[/tex] ( 0.033125)

∅ = 1.898 x 2

The angle of the first order = 2∅

2∅ = 4 degrees approximately

When n = 2

Sin∅ = nλ/d

Sin∅ = 2 x 530 x [tex]10^{-9}[/tex]/1.6 x [tex]10^{-5}[/tex]

Sin∅ = 0.06625

∅ = [tex]Sin^{-1}[/tex] ( 0.06625)

The angle of the second order = 2∅

2∅ = 3.7986 x 2

2∅ = 8 degrees approximately

Therefore, the angles of the first two orders are 4 degrees and 8 degrees approximately.

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