课程名称︰普通物理学乙 课程性质︰ 课程教师︰王建万 开课学院： 开课系所︰农化系 考试日期（年月日）︰2011.4.27 考试时限（分钟）：110分 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 题末附:第九版<章节-题号> 1. A parallel-plate capacitor has plates of area 0.12m^2 and a seperation of 1.44cm. A battery charges the plates to a potential difference of 160V and is then disconnected. A dielectric slab of thickness 4.8mm and dielectric constant 3.6 is then placed symmetrically between the plates. (a) What is the capacitance before the slab is inserted? (b) What is the capacitance with the slab in place? What is the free charge q (c) before and (d) after the slab is inserted? What is the magnitude of the electric field (e) in the place between the plates and dielectric and (f) in the dielectric itself? (g) With the slab in the place, what is the potential difference across the plates? (h) How much external work involved in inserting the slab? (15%) <25-53> 2.Two isolated, concentric, conducting spherical shells have radii R1=0.400m and R2=1.00m, uniform charges q1=+4.00μC and q2=+2.00μC, and negligible thicknesses.What is the magnitude of the electric field E at radial distance (a) r=4.00m, (b) r=0.700m, and (c) r=0.200m? With V=0 at infinity, what is V at (d) r=4.00m, (e) r=1.00m, (f) r=0.700m, (g) r=0.500m, (h) r=0.200m, and (i)r=0? (15%) <24-66> 3.What is the current in a wire of radius R=3.60mm if the magnitude of the current density is given by (a) Ja=Jo (r/R)^2 and (b) Jb=Jo(1-r/R)^2, in which r is the radial distance and Jo=5.50×10^4 A/m^2? (c) Which function maximizes the current density near the wire's surface? (9%) <26-11> 4.An electron follows a heilcal path in a uniform magnetic field given by B = (30i-50j-30k)mT. At time t = 0, the electron's velocity is given by v = (30i-30j+50k)m/s. (a) What is the angel ψ between v and B? The electron's velocity changes with time. Do (b) its speed and(c)the angel ψ change with time? (d) What is the radius of the helocal path?(e)what is the pitch of the helical motion? (10%) [electron mass m=9.11x10^-31kg, electron charge q=-e=-1.60x10^-19C] <28-34> 5.Fig.1 shows a proton(p) on the central axis through a disk with a uniform charge density due to excess electrons.Three of those electrons are shown: electron ec at the disk center and electron es at opposite sides of the disk, at radius R from the center.The proton is initially at distancez=R=2.50cm from the disk.At that location, what are the magnitudes of(a)the electric field Ec due to ec and (b)the net electric field Es,net due ti the electrons es? The proton is then moved to z=R/12.0. What then are the magnitudes of (c) Ec and (d)Es,net at the proton's location? (e)From (a) and (c) we see that as the proton gets nearer to the disk, the magnitude of Ec increases. Why does the magnitude of Es,net decrease, as we see from (b) and (d)? (10%) <22-13> 6.In Fig.1, a solid sphere of radius a=3.00cm is concentric with a spherical conducting shell of inner radius b=2.00a and outer radius of c=2.40a. The sphere has a net uniform charge q1=+8.00fC; the shell has a net charge q2=-q1. What is the magnitude of the electric field at radial distances (a) r=0, (b)r=a/2.00, (c) r=a, (d) r=1.50a, (e) r=2.30a, and (f) r=3.50a? What is the net charge on the (g) inner and (h) outer surface of the shell? (14%) <23-49> 7.In the circuit of Fig.3, ε=1.6kV, C=8.5μF,R1=R2=R3=0.73MΩ.With C completely uncharged, switch S is suddenly closed at t=0. At t=0, what are (a)current i1 in resistor 1,(b)current i2 in resistor 2, and (c)current i3 in resistor 3? At t=∞, what are (d)i1,(e)i2,and (f)i3?What is the potential difference V across resistor 2 at (g)t=0 (h)t=∞? (15%) <27-63> 8. Fig.4 is a section of a conducting rod of radius R1 = 1.50mm and length L =14.00m inside a thin-walled coaxial conducting cylindrical shell of radius R2 = 10.00R1 and the same length L. The net charge on the rod is Q1=+3.80x10^-12C; that on the shell is Q2=-2.00Q1.What are the(a) magnitude E and (b) direction (radially inward or outward) of the electric field at radial distance r = 2.00R2? What are (c) E and (d) direction at r = 5.00R1? What is the charge on the(e) interior and (f) exterior surface of the shell? (12%) <23-29> --

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