课程名称︰近代物理 课程性质︰选修 课程教师︰杨志忠 开课学院：电资院 开课系所︰电机系 考试日期（年月日）︰1000512 考试时限（分钟）：180 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1.Describe how we can use X-ray diffraction to measure the lattice size of a crystal material. 2.Please give the energy levels of aparticle of m in mass in a box of L in length. 3.Please give the expression of the two key uncertainty principle, i.e., in the time-energy domain and the position-momentum domain(one-dimensional). 4.When the energy of a photon is exactly equal to the energy different between two energy states, this photon can be absorted for electron transition from the lower state to the upper state. However even when the photon energy is smaller than the energy different between the two states, the transition can still ouccer. Does this phenomenon disobey the energy conservation rule? Explain why. 5.What is the relationship between the elecron lifetime in the upper state and the emission spectral width due to the electron transition between the upper state and a lower state? 6.Under what condition the result of the quantum theory can approach theat of the classical theory? 7.In laser operation, what kind of photon emission dominates the emission mechanism before and after the threshold condition? 8.For laser operation, how can the laser systme receive the first photon for generating stimulated emission? 9.In a four-level system for laser operation, the electron transition between the two states E1 and E2 (E1>E2) correspends to stimulated emission. For efficient laser operation, do we prefer a longer or shorter electron lifetime in state E2? Why? Do we prefer a longer or shorter electron lifetime in state E1? Why? 10.In quantum mechanics, we assume that all the physical quantities are mathematical operators, what is the basis for deriving the Schroudinger equation? 11.Can <p> or <E> be complex number? Explain why. Here, p and E represent the momentum and energy of a particle, repectively. Also, < > represents the expectation value and p stands for the momentum. 12.Explain tje different between <p^2> and <p>^2. Here, < > represents the expectation value and p stands for the momentum. 13.Describe the basic mathematical properties of a set of eigenfunction of a potential energy system. 14.Consider a symmetric quantum well structure. If we know that there are four even confined states in this quantum well, how many odd confined states in this quantum well? 15.In duality of a particle, what is the relationship between its momentum and its propagation vector? Note that both of them are vectors. 16.Please explain the difference of the energies of a harmonic oscillator between classical physics and quantum mechanics. 17.In a tunneling process of 10^12 electrons, only 10^6 electrons can transmit. If the thickness of the potential barrier becomes four times, Please estimate the new transmission probability. 18.In a symmetric quantum well, if the well width is increase, does the confined state number increase or decrease? If the well width is increase, does the confined state number increase or decrease? 19.In laser operation, when the pumping strength reaches the threshold condition, if we further increase the pumping strength, will the population inversion density be increased at the new steady state? Please describe the response of the system to ther further increase of pumping strength. 20.Based on Bohr's atomic theory, what is the physical meaning of the Bohr radius? --

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