课程名称︰普通物理学乙 课程性质︰必修 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）︰2012.6.20 考试时限（分钟）：120分钟 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1. A plane electromagnetic wave, with wavelength 2.50m, travels in vacuum in the direction of an x axis. The electric field, of amplitude 350 V/m, oscillates parallel to the y axis. What are the (a) frequency, (b) angular frequency, and (c) angular wave number of the wave? (d) what is the amplitude of the magnetic field component? (e) Parallel to which axos does the magnetic field wscillate? (f) What is the time averaged rate of energy flow in watts per square meter associated with this wave? The wave uniformly illuminates a furface of 2.40m^2. If the furface totally absorbs the wave, what are (g) the rate at which momentum is transferred to the surface and (h) the radiation pressure on the surface? 2. In Fig.1 (Holiday第九版 Fig.35-38) , two isotropic point sources S1 and S2 emit light in phase at wavelength λ and at same amplitude. The sources are separated by distance 2d=5.00λ. They lie on an axis that is parallel to an x axis,which runs along a viewing screen at distance D=30.0λ. The origin lies on the perpendicular bisector between the sources. The figure shows two rays reaching point P on the screen, at position Xp. (a) At what valur of Xp do the rays have the minimum phase difference? (b) What multiple of λ gives that minimum phase difference? (c) At what value of Xp do the rays have the maximum possible phase difference? What multiple of λ gives (d) that maximum phase difference and (e) the phase difference when Xp=6.00λ? (f) When Xp=6.00λ, is the resulting intensity at point P maximum, minimum, intermediate but closer to maximum, or intermediate but closer to minimum? 3. The full width at half-maximum (FWHM) of a central diffraction maximum is defined as the angle between the two points in the pattern.(See Fig.2) (课本Fig.36-8) (a) Show that the intensity drops to one-half the maximum value when (sinα)^2=α^2/2. (b) Verify that α=1.39rad(80°) is a solutionto the transcendental equation of (a) . (c) Show that the FWHM is △θ=2(sin)^-1 (0.443λ/a), where a is the slit width. Calculate the FWHM of the central maximum for slit width (d) 1.00λ (e) 5.00λ (f) 8.00λ. 4. Fig.3 (课本Fig31-35) shows an ac generator connected to a 'black box' through a pair of terminals. The box contains an RLC circuit, possibly even a multiloop circuit, whose elements and cinnections we do not know. Measurements outside the box reveal that ε(t)=(100.V)sinωdt and i(t)=(1.40A)sin(ωdt+42.0°). (a) What is the power factor? (b) Does the current lead or lag the emf? (c) Is the circuit in the box largely inductive or largely capacitive? (d) Is the cirvuit in the box in resonance? (e) Must there be a capacitor in the box? (f) An inductor? (g) A resistor? (h) At what average rate is the energy delivered to the box by the generator? (i) Why do not you need to know ωd to answer all these questions? 5. Fig.4a (课本Fig.32-34) shows the vurrent i that is produced in a wire of resistivity 1.84x10^-8Ω.m.The magnitude of the current versus t is shown in Fig.4b. The vertical axis scale is set by Is=12.5A, and the horizontal axis scale is set by ts=60.0ms. Point P is at radial distance 1.20cm from the wire's center. Determine the magnitude of the magnetic field Bi at point P due to the actual current i in the wire at (a) t=24.0ms, (b) t=48.0ms, and (c) t=72.0ms. Next, assume that the electri field driving the current is confined to the wire. Then determine the magnitude of the magnetic field Bid at point P due to the dicplacement current Id in the wire at (d) t=24.0ms, (e) t=48.0ms, (f) t=72.0ms. At point P at t=10.0s what is the direction (into or out of the page) of (g) Bi, (h) Bid. 6. Fig.5 (课本Fig.29-87) shows a cross section of a long conducting coaxial cable and gives its radii (a,b,c). Equal but opposite currents i are uniformly distributed in the two cinductors. Derive expressions for B(r) with radial distance r in the ranges (a)r<c, (b) c<r<b, (c) b<r<a, (d) r<a. Assume that a=2.00cm, b=1.60cm, c=0.40cm, i=160A. Calculate B(r) at (e) r=2.40cm (f) r=1.80cm, (g) r=0. 7. The conducting rodshown in Fig.6 (课本Fig.30-50) has length L and is being pulled along horozontal, frictionless cinducting rails at a constant velocity v. The rails are cinnected at one end with a metal strip. A uniform magnetic field B, directed out of the page, fills the region in which the rod moves. Assume that L=16.0cm, v=5.00m/s, and B=1.60T. What are the (a) magnitude and (b) direction (up or down the page)of the wmf induced in the rod? What are the (c) size and (d) direction of the current in the conducting loop? Assume that the resistance of the rod is 0.600Ω and that the resistance of the rails and metal strip is negligibly small. (e) At what rate is the thermal energy being generated in the rod? (f) What external force on the rod is needed to maintain v? (g) At what rate does this force do work on the rod? --

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