※ [本文转录自 NTU-Exam 看板] 作者: rexx () 看板: NTU-Exam 标题: [试题] 94下 张颜晖 普通物理甲 期末考 时间: Wed Jun 28 17:50:50 2006 课程名称︰普通物理学甲 课程性质︰ 课程教师︰张颜晖 开课系所︰电机系 考试时间︰2006/6/27 是否需发放奖励金：是XD （如未明确表示，则不予发放） 试题 : 1. Assume that a electron of mass m and charge e moves in a circular orbit of radius r about a nucleus. A magnetic field B is then applied perpendicular to the plane of the orbit. Assuming also that the radius of the orbit does not change and that the change in speed of the electron due to B is small, find an expression for the change in magnetic moment of the electron due to the field.(10) 2. In Fig.1, a laser beam of power 5W and diameter 2 mm is directed upward at one circular face (of diameter d<2mm) of a perfectly reflecting cylinder. the cylinder is lavitated because the upward radiation force matches the downward gravitation force. If the cylinder's density is 1g/cm^3, what is its height H.(10) 3. show that the simple magnifying lens has an angular magnification m_θ= 25cm/f, where f is the focal length (in cm) of the simple magnifier.(10) 4. Three EM wave travel through a certain point P along x-axis. They are polarized parallel to the y-axis. With the following variation in their amplitude. E1=(10.0mV/m)sin[(2.0x10^14 rad/s)t], E2=( 5.0mV/m)sin[(2.0x10^14 rad/s)t+45度], E3=(10.1mV/m)sin[(2.0x10^14 rad/s)t-30度]. Find the resultant electric field at P.(10) 5. A monochromatic beam of parallel light is incident on a "collimating" hole of a diameter x>>λ. Point P lies in the geometric shadow region on a distant screen. (see Fig.2 (a)). Two diffracting object, shown in Fig.2 (b), are placed in turn over the collimating hole. Object A is an opaque circle with a hole in it and B is the photographic negative of A. Using principle of superposition show that the intensity at P identical for the two diffracting object A and B.(10) 6. Show that the resolving power of a grating is given by R=Nm, where N is the number of ruling in the grating and m is the order of diffraction. (Note for N slit diffraction ( I(θ)=Im cos^2αsinNβ/Nsinβ, α=πasinθ/λ, β=πdsinθ/λ, a is the slit width and d is the distant between adjacent slits. Dispersion D=Δθ/Δλ)(10) 7. Write down the four Maxwell equations and explain the meaning of the equations in common language (remember E and B are vectors and make sure integral is a integrate around a surface or a circle). Write down the one dimensional time independent Schrodinger equation for a particle of mass m in a potential U(x). For the wavefunction ψ(x) with eigenenergy E write down the time dependent wavefunction ψ(x,t). What is the probability of finding the particle between x and x+dx.(10) 8. In a Compton scattering experiment, show that Δλ=h/mc(1-cosψ), where ψ is the angle between the incoming photon and the scattered photon, and m is the rest mass of the electron.(10) 9. Find the energy level of an electron in a rectangular quantum dots of size a If there are a total of 12 electrons in the quantum dots, what is the total energy of the electrons. (Dont forget that one electron has two spin states) (10) 10. In a experiment similar to the Stern-Gerlach experiment shown in Fig.3, a beam of unknown atoms was sent through a nonuniform magnetic field. If the beam split into five parts after it passed through the B field, assume the total spin of the atom is zero, what is the total orbital angular momentum of the atoms? Assume the gradient of the magnetic field dB/dz=a, what is the force acting on the atom when the atoms were passing through the magnetic field? (In the answer please express μ_s,z in term of Bohr magneton)(10) 11. Explain what are spontaneous emission, stimulated absorption and stimulated emission. How to create a population inversion? Explain why the resonant cavity could make the laser beam highly directional.(10) --

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