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Why Don't We Diffract? (a) Calculate the de Broglie wavelength of a typical person walking through a doorway. Make reasonable approximations for the necessary quantitics. (b) Will the person in part (a) exhibit wave-like behavior when walking through the "single slit" of a doorway? Why?

Short Answer

Expert verified
The de Broglie wavelength is too small for wave-like behavior to be noticeable.

Step by step solution

01

Estimate Necessary Quantities

To calculate the de Broglie wavelength, we need the mass and velocity of the person. Assume an average mass (m) of 70 kg and an average walking speed (v) of 1.4 m/s.
02

Use the de Broglie Wavelength Formula

The de Broglie wavelength (\(\lambda\) ) is given by the formula: \[\lambda = \frac{h}{mv}\]where \(h\) is Planck's constant (\(6.626 \times 10^{-34} \text{ J} \cdot \text{s}\) ). Plug in the values:\[\lambda = \frac{6.626 \times 10^{-34}}{70 \times 1.4}\]
03

Perform the Calculation

Calculate the de Broglie wavelength:\[\lambda = \frac{6.626 \times 10^{-34}}{98} = 6.76 \times 10^{-36} \text{ meters}\]The de Broglie wavelength of the person is approximately \( 6.76 \times 10^{-36} \) meters.
04

Compare Wavelength to Doorway

Typical doorway widths are about 0.8 meters. The de Broglie wavelength (\(6.76 \times 10^{-36} \text{ meters}\)) is much smaller than the doorway width. Thus, any wave-like behavior or diffraction effects would be imperceptibly small.
05

Conclusion on Wave-like Behavior

Given the significantly larger width of the doorway compared to the de Broglie wavelength, the person will not exhibit any wave-like behavior while walking through the doorway.

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Key Concepts

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

Quantum Mechanics
Quantum mechanics is the remarkable field of physics that explains the peculiar behavior of particles at very small scales, like atoms and subatomic particles. Unlike classical physics, which deals with the macroscopic world, quantum mechanics introduces unusual concepts that challenge our common experience. One of these concepts is the quantization of energy levels, meaning that certain properties, like energy, can only take on specific discrete values.

In the quantum world, particles also exhibit a kind of duality, embodying characteristics of both particles and waves. Quantum mechanics utilizes complex mathematical frameworks and probabilistic principles to predict the behavior and interaction of particles. It explains phenomena like atomic spectra, superconductivity, and the photoelectric effect.

Understanding quantum mechanics is crucial because it helps us elucidate how light and matter behave on these incredibly small scales, influencing technologies such as semiconductors and MRI scanners. Despite its abstract nature, quantum mechanics heavily impacts modern technology, allowing for advancements that classical theories can’t fully address.
Wave-Particle Duality
Wave-particle duality is a core concept in quantum mechanics that proposes particles, such as electrons and photons, exhibit both wave and particle characteristics. This duality allows particles to behave like waves in some situations, producing interference patterns and diffraction, while in other scenarios, they exhibit particle properties such as discrete impacts.

The idea became prominent with experiments like the double-slit experiment, where particles create an interference pattern typical of waves when unobserved, but behave like particles when measured. This duality is significant because it challenges the classical understanding of particles solely as localized objects, introducing the concept of the de Broglie wavelength, which calculates the wave nature of matter based on its momentum.

For a person walking through a doorway, the de Broglie wavelength is imperceptibly small due to their large mass and relatively slow speed. Therefore, while individuals technically possess a de Broglie wavelength, any wave-like behavior is negligible, emphasizing how wave-particle duality becomes more pronounced at microscopic scales.
Diffraction
Diffraction is a phenomenon that occurs when waves encounter an obstacle or a slit that is comparable in size to their wavelength, causing them to spread out and create interference patterns. It is an essential concept in understanding the behavior of waves, whether sound, light, or matter waves.

One classic example of diffraction is light passing through narrow slits and producing a pattern of bright and dark fringes. Diffraction provides evidence of the wave nature of light and matter, as it is a behavior specific to waves.

In the context of a person walking through a doorway, the de Broglie wavelength calculated is so minuscule compared to the width of a typical doorway that the person would not exhibit noticeable wave-like diffraction patterns. This shows how diffraction effects become significant when the size of an opening is similar to the wavelength of the wave passing through, explaining why we don't observe such phenomena in everyday life for large objects like people.

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Most popular questions from this chapter

Imagine another universe in which the value of Planck's constant is \(0.0663 \mathrm{J} \cdot \mathrm{s},\) but in which the physical laws and all other physical constants are the same as in our universe. In this universe, two physics students are playing catch. They are 12 \(\mathrm{m}\) apart, and one throws a \(0.25-\mathrm{kg}\) ball directly toward the other with a speed of 6.0 \(\mathrm{m} / \mathrm{s}\) (a) What is the uncertainty in the ball's horizontal momentum, in a direction perpendicular to that in which it is being thrown, if the student throwing the ball knows that it is located within a cube with volume 125 \(\mathrm{cm}^{3}\) at the time she throws it? (b) By what horizontal distance could the ball miss the second student?

An electron has a de Broglie wavelength of \(2.80 \times 10^{-10} \mathrm{m}\) . Determine (a) the magnitude of its momentum and \((b)\) its kinetic energy (in joules and in electron volts).

The wave nature of particles results in the quantum- mechanical situation that a particle confined in a box can assume only wavelengths that result in standing waves in the box, with nodes at the box walls, (a) Show that an electron confined in a one- dimensional box of length \(L\) will have energy levels given by $$E_{n}=\frac{n^{2} h^{2}}{8 m L^{2}}$$ (Hint: Recall that the relationship between the de Broglic wave- length and the speed of a nonrelativistic particle is \(m v=h / \lambda\) . The energy of the particle is \(\frac{1}{2} m v^{2}, )(b)\) If a hydrogen atom is modeled as a one-dimensional box with length equal to the Bohr radius, what is the energy (in electron volts) of the lowest energy level of the electron?

By extremely careful measurement, you determine the \(x\) -coondinate of a car's center of mass with an uncertainty of only 1.00\(\mu \mathrm{m}\) . The car has a mass of 1200 \(\mathrm{kg}\) . (a) What is the minimum uncertainty in the \(x\) -component of the velocity of the car's center of Mass as presuribed by the Heisenberg uncertainty principle? (b) Does the uncertainty principle impose a practical limit on our ability to make simultaneous measurements of the positions and velocities of ordinary objects like cars, books, and people? Explain.

Particle \(A\) is described by the wave function \(\psi(x, y, z)\) . Particle \(B\) is described by the wave function \(\psi(x, y, z) e^{i \phi}\) , where \(\phi\) is a real constant. How does the probability of finding particle \(A\) within a volume \(d V\) around a certain point in space compare with the probability of finding particle \(B\) within this same volume?

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