In a fraunhofer diffraction by single slit of width d with incident light of wavelength \(5500 \AA\) the first minimum is observed at angle of \(30^{\circ}\). The first secondary maximum is observed at an angle \(\theta=\) (A) \(\sin ^{-1}(1 / \sqrt{2})\) (B) \(\sin ^{-1}(3 / 4)\) (C) \(\sin ^{-1}(\sqrt{3} / 2)\) (D) \(\sin ^{-1}(1 / 4)\)

Short Answer

Expert verified
The angle for the first secondary maximum is given by: \( \theta_{max} = \sin^{-1}\left(\left(\frac{3}{2}\right)\frac{5500 × 1e-10}{d}\right) \) After substituting λ and d values and comparing to the given options, the correct answer is (B) \( \sin^{-1}(3 / 4) \).

Step by step solution

01

Convert the wavelength to meters

First, we need to convert the given wavelength of 5500 Å (which is in Angstroms) to meters. The conversion factor is 1 Å = 1e-10 meters. Therefore, the wavelength λ in meters is: λ = 5500 × 1e-10 m
02

Apply the Fraunhofer Diffraction Formula

For a single slit of width d, the angular position of the minima m in the Fraunhofer diffraction pattern is given by the formula: \( \sin \theta_{m} = \frac{m\lambda}{d} \) where m = 1, 2, 3... and θ is the angle between the central maximum and the minimum. We are given that the first minimum (m=1) is observed at an angle of 30°: \( \sin \theta_{1} = \frac{1\lambda}{d} \) Now, we can plug in the given angle and calculate the width of the slit.
03

Calculate the Width of the Slit

We know that the first minimum (m=1) appears at an angle of θ = 30°. Thus, \( \sin(30^{\circ}) = \frac{1\lambda}{d} \) Solve for d: \( d = \frac{1\lambda}{\sin(30^{\circ})} \) Now, substitute the value of λ (converted to meters): \( d = \frac{1(5500 × 1e-10)}{\sin(30^{\circ})} \) Calculate the width of the slit, d.
04

Find the Angle for the First Secondary Maximum

The condition for the secondary maxima is given by the formula: \( \sin \theta_{max} = \left(\frac{2k+1}{2}\right)\frac{\lambda}{d} \) where k = 1, 2, 3... and represents the order of the secondary maxima. For the first secondary maximum, k = 1: \( \sin \theta_{max} = \left(\frac{2(1)+1}{2}\right)\frac{\lambda}{d} \) Now substitute the values of λ and d to find the angle: \( \sin \theta_{max} = \left(\frac{3}{2}\right)\frac{5500 × 1e-10}{d} \) Therefore, θ_max is given by: \( \theta_{max} = \sin^{-1}\left(\left(\frac{3}{2}\right)\frac{5500 × 1e-10}{d}\right) \) Finally, compare the value obtained for θ_max to the given options (A), (B), (C), and (D) to find the correct answer.

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