Chapter 5: Q62E (page 191)
What is the product of uncertainties determined in Exercise 60 and 61? Explain.
Short Answer
The product of uncertainty in position and momentum is , which is in accordance with the uncertainty principle.
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Chapter 5: Q62E (page 191)
What is the product of uncertainties determined in Exercise 60 and 61? Explain.
The product of uncertainty in position and momentum is , which is in accordance with the uncertainty principle.
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Outline a procedure for predicting how the quantum-mechanically allowed energies for a harmonic oscillator should depend on a quantum number. In essence, allowed kinetic energies are the particle-in-a box energies, except the length Lis replaced by the distance between classical tuning points. Expressed in terms of E. Apply this procedure to a potential energy of the form U(x) = - b/x where b is a constant. Assume that at the origin there is an infinitely high wall, making it one turning point, and determine the other numing point in terms of E. For the average potential energy, use its value at half way between the tuning points. Again in terms of E. Find and expression for the allowed energies in terms of m, b, and n. (Although three dimensional, the hydrogen atom potential energy is of this form. and the allowed energy levels depend on a quantum number exactly as this simple model predicts.)
Advance an argument based on that there is no bound state in a half-infinite well unless is at least. (Hint: What is the maximum wavelength possible within the well?)
Show that the uncertainty in a particle鈥檚 position in an infinite well in the general case of arbitrary is given by
Discuss the dependence. In what circumstance does it agree with the classical uncertainty of discussed in Exercise 55?
What is the probability that the particle would be found between x = 0and x = 1/a?
In Section 5.5, it was shown that the infinite well energies follow simply from the formula for kinetic energy, p2/2m; and a famous standing-wave condition, . The arguments are perfectly valid when the potential energy is 0(inside the well) and L is strictly constant, but they can also be useful in other cases. The length L allowed the wave should be roughly the distance between the classical turning points, where there is no kinetic energy left. Apply these arguments to the oscillator potential energy, .Find the location x of the classical turning point in terms of E; use twice this distance for L; then insert this into the infinite well energy formula, so that appears on both sides. Thus far, the procedure really only deals with kinetic energy. Assume, as is true for a classical oscillator, that there is as much potential energy, on average, as kinetic energy. What do you obtain for the quantized energies?
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