Chapter 39: Q. 41 (page 1118)
What is the smallest one-dimensional box in which you can confine an electron if you want to know for certain that the electron's speed is no more than ?
Short Answer
The smallest one-dimensional box is
Chapter 39: Q. 41 (page 1118)
What is the smallest one-dimensional box in which you can confine an electron if you want to know for certain that the electron's speed is no more than ?
The smallest one-dimensional box is
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Get started for freeFIGURE Q39.6 shows wave packets for particles 1, 2, and 3. Which particle can have its velocity known most precisely? Explain.
A -mm-diameter sphere bounces back and forth between two walls at and . The collisions are perfectly elastic, and the sphere repeats this motion over and over with no loss of speed. At a random instant of time, what is the probability that the center of the sphere is
a. At exactly ?
b. Between and ?
c. At ?
FIGURE EX39.13 shows the probability density for an electron that has passed through an experimental apparatus. What is the probability that the electron will land in a -wide strip at (a) , (b), (c) , and (d) ?
a. Starting with the expression for a wave packet, find an expression for the product for a photon.
b. Interpret your expression. What does it tell you?
c. The Bohr model of atomic quantization says that an atom in an excited state can jump to a lower-energy state by emitting a photon. The Bohr model says nothing about how long this process takes. You'll learn in Chapter 41 that the time any particular atom spends in the excited state before cmitting a photon is unprcdictablc, but the average lifetime of many atoms can be determined. You can think of as being the uncertainty in your knowledge of how long the atom spends in the excited state. A typical value is ns. Consider an atom that emits a photon with a wavelength as it jumps down from an excited state. What is the uncertainty in the energy of the photon? Give your answer in eV.
d. What is the fractional uncertainty in the photon's energy?
Soot particles, from incomplete combustion in diesel engines, are typically in diameter and have a density of . FIGURE P39.45 shows soot particles released from rest, in vacuum, just above a thin plate with a -diameter holeroughly the wavelength of visible light. After passing through the hole, the particles fall distance and land on a detector. If soot particles were purely classical, they would fall straight down and, ideally, all land in a -diameter circle. Allowing for some experimental imperfections, any quantum effects would be noticeable if the circle diameter were . How far would the particles have to fall to fill a circle of this diameter?
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