Accumulation of Charges - General Physics - Past Paper, Exams of Physics

Download Accumulation of Charges - General Physics - Past Paper and more Exams Physics in PDF only on Docsity! St. Vincent College PH 112: General Physics II Final Exam 5/3/2005 The exam consists of 8 questions. There will be 2 hours to complete the exam. The questions may not be worth the same number of points, read the entire exam before beginning work. Put your name on all pages. Problem 1 20 Problem 2 30 Problem 3 30 Problem 4 25 Problem 5 20 Problem 6 25 Problem 7 25 Problem 8 25 Total 1. (20 pts) a) (5 pts) When a capacitor is charging, there is a magnetic field created in the region of space between the plates in addition to the electric field due to the accumulation of charges on the plates. What is it that causes this magnetic field when there are no charges moving through this region of space (ie. no current)? b) (5 pts) According to the currently accepted theory of light, is there a “dual-nature” to the way light behaves? If so, explain. If not, how does it behave? c) (5 pts) At one instant of time, the electric field of a certain E-M wave is pointing in the +k̂ direction while the magnetic field is pointing in the −ĵ direction. In what direction is the wave propagating? d) (5 pts) A positive charge is released in a region of space containing an electric field. The charge is observed to accelerate in the +k̂ direction. Is the electric potential in this region of space increasing or decreasing as one travels in this direction? 4. (25 pts) An infinite sheet of conductor has a net positive charge Q resulting in a surface charge density σ on both surfaces, as shown below in cross-section. Use Gauss’s Law to determine the electric field on either side of the plate. You may wish to draw your Gaussian surface on the figure below to aid your computations (and to increase the possibility of partial credit in the event that something else goes wrong). + + + + + + 5. (20 pts) a) (5 pts) Explain why, physically, the net magnetic flux through a closed surface must be zero. b) (5 pts) Three long, parallel wires carry currents of equal magnitudes. Can the direction of these currents be arranged such that all three wires are repelled from each other? c) (5 pts) Does the fact that index of refraction depends on the wavelength of the incident light affect the manner in which the light is reflected from the surface? If so, how? d) (5 pts) A loop of wire is motionless in a magnetic field. The magnetic field is perpendicular to the plane of the loop. However, there is no current nor potential induced in the loop. What can be said about the magnetic flux through the loop? 6. (25 pts) As was mentioned in class, the goal of electromagnetic theory is to predict the net force on a charged particle in the presence of other charges which may also be moving (ie. currents). The usual way to do this is to find (a) the electric field due to the other charges and then (b) the magnetic field due to the current if the charges are moving. The net force on the charged particle may then be determined Consider a region of space in which the electric field at some instant is given by ~E = 2000 î− 3500 k̂ V/m and the magnetic field by ~B = 0.2 ĵ + 0.9 k̂ T A singly ionized 6C12 ion is fired into this region of space with a velocity ~v = 1.5 × 103 î− 2.0 × 103 ĵ m/s What is the resulting net force on this ion? (You may leave your answer in terms of vector components if that is easier for you.)