Chapter 39: Q.25 (page 1137)
What is the minimum uncertainty in position, in , of an electron whose velocity is known to be between and ?
Short Answer
Round off to two significant figures, the minimum uncertainty in position of the electron is
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Chapter 39: Q.25 (page 1137)
What is the minimum uncertainty in position, in , of an electron whose velocity is known to be between and ?
Round off to two significant figures, the minimum uncertainty in position of the electron is
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Physicists use laser beams to create an atom trap in which atoms are confined within a spherical region of space with a diameter of about . The scientists have been able to cool the atoms in an atom trap to a temperature of approximately , which is extremely close to absolute zero, but it would be interesting to know if this temperature is close to any limit set by quantum physics. We can explore this issue with a onedimensional model of a sodium atom in a -long box.
a. Estimate the smallest range of speeds you might find for a sodium atom in this box.
b. Even if we do our best to bring a group of sodium atoms to rest, individual atoms will have speeds within the range you found in part a. Because there's a distribution of speeds, suppose we estimate that the root-mean-square speed of the atoms in the trap is half the value you found in part a. Use this to estimate the temperature of the atoms when they've been cooled to the limit set by the uncertainty principle.
What is the value of the constant a in FIGURE Q39.5?

Andrea, whose mass is , thinks she's sitting at rest in her 5.0-m-long dorm room as she does her physics homework. Can Andrea be sure she's at rest? If not, within what range is her velocity likely to be?
Consider the electron wave function
a. Determine the normalization constant c. Your answer will be in terms of L.
b. Draw a graph of over the interval -Lx 2L.
c. Draw a graph of over the interval -L x 2L. d. What is the probability that an electron is in the interval 0 x L/3?
FIGURE Q39.1 shows the probability density for photons to be detected on the-axis.
a. Is a photon more likely to be detected at or at ? Explain.
b. One million photons are detected. What is the expected number of photons in a -wide interval at ?

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