中南大学双语物理月日试卷.docVIP

09 Question One. Fill in the blanks (24 marks total, 4 marks each) 1. The surface charge density of a conductor of arbitrary shape in vacuum is . Then the electric field near the conductor’s surface has magnitude and its direction is . 2. The electric potential at points in an xy plane is given by . Find the magnitude and direction of the electric field at point (1, 2). E = ___, and the direction is __ . 3. An alternating voltage of the form is applied across an air-filled parallel-plate capacitor of area A and separation d. Find (a) the electric flux through a surface between the two plates of the capacitor with area A and parallel to the plates, and (b) the displacement current in the capacitor. = ___, =____. Fig. 1-1 4. A conducting rod MN of length L located on the horizontal plane rotates about point O, a distance L/3from end N, at a constant angular speed ? .A uniform magnetic field points upward vertically (Fig.1-1). The magnitude of the motional emf in the rod is . Which end of the rod has higher potential? . 5. In vacuum, the energy density of an electromagnetic wave at a point is . The ratio of E to B is . 6. The energy required for the quantum jump of the electron in ground state to the energy level with n=4 in hydrogen atom is . The number of spectra lines that this excited electron can emit is . Question Two. Multiple-choice questions (30 marks total, 3 marks each) Fig.2-1 1. Figure 2-1 shows the electric field lines of concentric conducting solid sphere and conducting spherical shell. Then the spherical shell is (a) positively charged；(b) electrically neutral; (c) negatively charged; (d) not enough information. 2. An infinitely long straight charged plastic rod with uniform linear charge density ? is placed in vaccum, and then electric field energy density at a point, a distance r from the rod, is given by (a) ; (b) ; (c) ; (d) . 3. An electron with charge e moves in a circle of radius r at a constant speed v,