Chapter 42: Problem 32
It is proposed to send a beam of electrons through a diffraction grating. The electrons have a speed of 400 \(\mathrm{m} / \mathrm{s}\). How large must the distance between slits be if a strong beam of electrons is to emerge at an angle of \(25^{\circ}\) to the straight-through beam?
Short Answer
Expert verified
The slit distance must be calculated using \(d = \frac{\lambda}{\sin(25^\circ)}\), where \(\lambda\) is the de Broglie wavelength.
Step by step solution
01
Understand the problem
We need to find the distance between slits of a diffraction grating that allows electrons moving at 400 m/s to produce a strong beam at a 25-degree angle.
02
Use the de Broglie wavelength formula
Calculate the wavelength of the electrons using the de Broglie wavelength formula \( \lambda = \frac{h}{mv} \), where \( h \) is Planck's constant \(6.63 \times 10^{-34} \text{ m}^2 \text{ kg} / \text{s} \), \( m \) is the mass of an electron \(9.11 \times 10^{-31} \text{ kg}\), and \( v \) is the speed of the electrons \(400 \text{ m/s}\).
03
Calculate the electron wavelength
Substitute the known values into the de Broglie wavelength formula: \( \lambda = \frac{6.63 \times 10^{-34}}{9.11 \times 10^{-31} \times 400} \). This will give the wavelength of the electrons.
04
Use the diffraction grating formula
To find the slit spacing \(d\), use the diffraction grating formula \(d \sin(\theta) = m \lambda\), where \( \theta = 25^\circ \) and \(m\) is the order of diffraction (typically \(m = 1\) for the first strong beam).
05
Calculate the distance between slits
Substitute \( \lambda \) from Step 3 and \(\theta\) into the formula \(d = \frac{m \lambda}{\sin(\theta)}\) to find \(d\). Use \(\theta = 25^\circ\) and \(m = 1\).
06
Solve for the slit distance
Calculate \(d = \frac{1 \cdot \lambda}{\sin(25^\circ)}\) using the wavelength from Step 3 and the sine function to find the distance between slits.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
de Broglie wavelength
The de Broglie wavelength is a fundamental concept that connects the wave and particle nature of matter. According to the de Broglie hypothesis, particles such as electrons exhibit wave-like properties. This wavelength, denoted by \( \lambda \), can be calculated using the formula: \[ \lambda = \frac{h}{mv} \]Here:
- \( h \) is Planck's constant \( 6.63 \times 10^{-34} \text{ m}^2 \text{ kg} / \text{s} \)
- \( m \) is the mass of the particle, for an electron it is \( 9.11 \times 10^{-31} \text{ kg} \)
- \( v \) is the velocity of the particle, which in this exercise is \( 400 \text{ m/s} \)
electron diffraction
Electron diffraction explains how electrons can demonstrate wave-like behaviors, such as creating interference patterns. This occurs when a beam of electrons passes through a material, like a diffraction grating, that has closely spaced lines or slits. The spacing is comparable to the wavelength of the electrons. When these electrons encounter such a material, they undergo diffraction, a bending of waves around obstacles. Coinciding waves due to constructive interference intensify certain angles, creating visible patterns.In this exercise, we aim for a strong diffraction pattern at an angle of \( 25^{\circ} \). The way electrons spread depends significantly on their de Broglie wavelength, which was calculated earlier, and the structural design of the grating.
slit spacing
The slit spacing in a diffraction grating is critical in determining where strong beams or interference patterns appear. The distance between slits, denoted as \( d \), depends on the wavelength of the illumination and the desired angle of the beam.For electrons moving at a certain speed, the de Broglie wavelength gives us insight into appropriate slit spacing. In this case, you can find \( d \) using the formula:\[ d = \frac{m \lambda}{\sin(\theta)} \]
- \( m \) represents the order of diffraction, which is often \( m = 1 \) for the first strong beam.
- \( \lambda \) is the wavelength calculated previously.
- \( \theta \) is the diffraction angle, \( 25^{\circ} \), in this situation.
diffraction angle
The diffraction angle is where electrons or any diffracted waves emerge after passing through a grating. In this setup, the desired diffraction angle, \( \theta \), is given as \( 25^{\circ} \).The angle tells us where the principal maximum, or strong beam, will appear following interaction with the grating. It is significantly influenced by several factors:
- The de Broglie wavelength of the electrons
- The slit spacing in the grating
- The order \( m \) of the maximum, commonly the first order \( m = 1 \)