Chapter 6: Q34E (page 226)
Question: Obtain equation (6.18) from(6.16) and (6.17).
Short Answer
Answer
The equation is derived from and
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Chapter 6: Q34E (page 226)
Question: Obtain equation (6.18) from(6.16) and (6.17).
Answer
The equation is derived from and
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Given the situation of exercise 25, show that
(a) as , reflection probability approaches 1 and
(b) as , the reflection probability approaches 0.
(c) Consider the limit in which the well becomes infinitely deep and infinitesimally narrow--- that is and data-custom-editor="chemistry" but the product U0L is constant. (This delta well model approximates the effect of a narrow but strong attractive potential, such as that experienced by a free electron encountering a positive ion.) Show that reflection probability becomes:
To obtain a rough estimate of the mean time required for uranium-238 to alpha-decay, let us approximate the combined electrostatic and strong nuclear potential energies by rectangular potential barrier half as high as the actual 35 Mev maximum potential energy. Alpha particles (mass 4 u) of 4.3 Mev kinetic energy are incident. Let us also assume that the barrier extends from the radius of nucleus, 7.4 fm to the point where the electrostatic potential drops to 4.3 Mev (i.e., the classically forbidden region). Because , this point is 35/4.3 times the radius of the nucleus, the point at which U(r) is 35 Mev. (a) Use these crude approximations, the method suggested in Section 6.3, and the wide-barrier approximation to obtain a value for the time it takes to decay. (b) To gain some appreciation of the difficulties in a theoretical prediction, work the exercise 鈥渂ackward鈥 Rather than assuming a value for U0, use the known value of the mean time to decay for uranium-238 and infer the corresponding value of U0, Retain all other assumptions. (c) Comment on the sensitivity of the decay time to the height of the potential barrier.

Exercise 39 gives a condition for resonant tunneling through two barriers separated by a space width of, expressed I terms of factorgiven in exercise 30. Show that in the limit in which barrier width, this condition becomes exactly energy quantization condition (5.22) for finite well. Thus, resonant tunneling occurs at the quantized energies of intervening well.
As we learn in physical optics, thin-film interference can cause some wavelengths of light to be strongly reflected while others not reflected at all. Neglecting absorption all light has to go one way or the other, so wavelengths not reflected are strongly transmitted. (a) For a film, of thickness t surrounded by air, what wavelengths 位 (while they are within the film) will be strongly transmitted? (b) What wavelengths (while they are 鈥渙ver鈥 the barrier) of matter waves satisfies condition (6-14)? (c) Comment on the relationship between (a) and (b).
Your friend has just finished classical physics and can鈥檛 wait to know what lies ahead. Keeping extraneous ideas and postulates to a minimum, Explain the process of Quantum-mechanical tunneling.
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