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(II) First-order Bragg diffraction is observed at \(26.8^{\circ}\) relative to the crystal surface, with spacing between atoms of \(0.24 \mathrm{nm} .\) ( \(a\) ) At what angle will second order be observed? (b) What is the wavelength of the X-rays?

Short Answer

Expert verified
(a) Second order angle is approximately \(64.16^\circ\). (b) Wavelength of X-rays is \(0.216 \text{ nm}\).

Step by step solution

01

Understanding Bragg's Law

Bragg's Law relates the angle at which X-rays are diffracted to the spacing between atomic layers in a crystal. It's given by the formula: \( n\lambda = 2d\sin(\theta) \), where \(n\) is the order of the diffraction, \(\lambda\) is the wavelength, \(d\) is the spacing between atomic layers, and \(\theta\) is the diffraction angle.
02

Substitute Given Data for First Order

For first-order diffraction (\(n = 1\)), you are given \(\theta = 26.8^\circ\) and \(d = 0.24\, \text{nm}\). Substitute these into Bragg's Law to find the wavelength: \( \lambda = \frac{2 \cdot 0.24 \sin(26.8^\circ)}{1} \). Use a calculator to find \(\lambda\) in nanometers.
03

Calculate Wavelength of X-rays

Using the calculator: \( \lambda = \frac{2 \cdot 0.24 \sin(26.8^\circ)}{1} = 0.216 \, \text{nm} \). This is the wavelength of the X-rays.
04

Setup Bragg's Law for Second Order

For the second-order diffraction, set \(n = 2\) in Bragg's Law: \( 2\lambda = 2d\sin(\theta_2) \). You know \(\lambda\) and \(d\), so solve for \(\theta_2\).
05

Solve for Second Order Angle

Rearrange the equation: \( \sin(\theta_2) = \frac{2 \cdot 0.216}{2 \cdot 0.24} = \frac{0.216}{0.24} \). Calculate \(\sin^{-1}\) to determine \(\theta_2\).
06

Calculate Second Order Angle

\(\sin(\theta_2) = 0.9\). Therefore, \(\theta_2 = \sin^{-1}(0.9) \approx 64.16^\circ\). The second-order diffraction will be observed at \(\theta_2 = 64.16^\circ\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

X-ray diffraction
X-ray diffraction is a process that helps scientists understand the structure of crystals. When X-ray beams hit a crystal, they are scattered by the electrons around the atoms. This scattering creates a pattern.
The pattern can tell researchers about the spacing between atoms, which is essential for identifying materials.
The phenomenon of X-ray diffraction was first explained by physicists William Lawrence Bragg and his father in 1913. Their explanation, known as Bragg's Law, provides a mathematical relationship:
  • Diffraction occurs when the distance the wave travels between layers is a whole number of wavelengths.
  • This condition is expressed in the formula: \[ n\lambda = 2d\sin(\theta) \]where \( n \) is the order of reflection, \( \lambda \) is the wavelength, \( d \) is the distance between atomic layers, and \( \theta \) is the angle of diffraction.
Understanding this process is crucial for fields like chemistry, physics, and even medicine because it allows for the characterizing and discovery of new materials.
atomic layer spacing
Atomic layer spacing, symbolized as \( d \) in Bragg's Law, is the distance between planes of atoms in a crystal. This spacing is crucial because it affects how X-rays are diffracted.
Different materials have unique atomic layer spacings determining the angles at which X-rays will diffract.
In the given problem, the atomic layer spacing is given as \( 0.24 \, \text{nm} \). This exact spacing influences the angle at which we will observe the diffraction peaks.
  • The greater the spacing, the wider the potential range for diffraction.
  • This spacing is vital for calculating the correct wavelength of X-rays in the system, as well as predicting where higher orders of diffraction may be observed.
Understanding and calculating atomic layer spacing is essential for using Bragg's Law to analyze crystal structures effectively.
wavelength calculation
Calculating the wavelength of X-rays is critical in the context of X-ray diffraction. It allows one to understand the characteristics of the radiation used.
X-rays have very short wavelengths that can probe the distances between atoms. In the context of Bragg's Law, the wavelength \( \lambda \) is unknown and needs to be determined using the given diffraction angle.
In the provided solution, the formula\[ \lambda = \frac{2d\sin(\theta)}{n} \]is used to find the wavelength. For the first-order diffraction (\( n = 1 \)), substituting the given values,- \( \theta = 26.8^{\circ} \)- \( d = 0.24 \, \text{nm} \)We calculate:\[ \lambda = \frac{2 \cdot 0.24 \cdot \sin(26.8^{\circ})}{1} = 0.216 \, \text{nm} \]This calculation provides the wavelength of the X-rays, which can then be used to determine where higher-order diffraction peaks, like the second-order, will occur.
  • Calculating the wavelength accurately is vital for correctly interpreting the diffraction patterns and understanding the material being studied.
  • Each value influences the accuracy of determining the crystal's structure.
Understanding wavelength and its calculation are key to successfully applying Bragg's Law in practical scenarios.

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Most popular questions from this chapter

When yellow sodium light, \(\lambda=589 \mathrm{nm},\) falls on a diffraction grating, its first-order peak on a screen \(66.0 \mathrm{~cm}\) away falls \(3.32 \mathrm{~cm}\) from the central peak. Another source produces a line \(3.71 \mathrm{~cm}\) from the central peak. What is its wavelength? How many lines/cm are on the grating?

(II) A diffraction grating has 16,000 rulings in its \(1.9 \mathrm{~cm}\) width. Determine \((a)\) its resolving power in first and second orders, and \((b)\) the minimum wavelength resolution \((\Delta \lambda)\) it can yield for \(\lambda=410 \mathrm{nm}\)

(II) A diffraction grating has \(6.0 \times 10^{5}\) lines \(/ \mathrm{m} .\) Find the angular spread in the second-order spectrum between red light of wavelength \(7.0 \times 10^{-7} \mathrm{m}\) and blue light of wavelength \(4.5 \times 10^{-7} \mathrm{m} .\)

(III) The percent polarization \(P\) of a partially polarized beam of light is defined as $$ P=\frac{I_{\max }-I_{\min }}{I_{\max }+I_{\min }} \times 100 $$ where \(I_{\text {max }}\) and \(I_{\text {min }}\) are the maximum and minimum intensities that are obtained when the light passes through a polarizer that is slowly rotated. Such light can be considered as the sum of two unequal plane-polarized beams of intensities \(I_{\max }\) and \(I_{\min }\) perpendicular to each other. Show that the light transmitted by a polarizer, whose axis makes an angle \(\phi\) to the direction in which \(I_{\max }\) is obtained, has intensity $$ \frac{1+p \cos 2 \phi}{1+p} I_{\max } $$ where \(p=P / 100\) is the "fractional polarization."

(a) How far away can a human eye distinguish two car headlights \(2.0 \mathrm{~m}\) apart? Consider only diffraction effects and assume an eye diameter of \(6.0 \mathrm{~mm}\) and a wavelength of \(560 \mathrm{nm} .(b)\) What is the minimum angular separation an eye could resolve when viewing two stars, considering only diffraction effects? In reality, it is about \(1^{\prime}\) of arc. Why is it not equal to your answer in \((b) ?\)

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