Physics 102. First Midterm Examination Fall Semester 2015/2016. November 3, 2015 Time: 6.30 p.m p.m. Name. Student No..

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Kuwait University Physics Department Physics 102 First Midterm Examination Fall Semester 2015/2016 November 3, 2015 Time: 6.30 p.m. - 8.00 p.m. Name. Student No.. Section No. Instructors: Drs.

1 Kuwait University Physics Department Physics 102 First Midterm Examination Fall Semester 2015/2016 November 3, 2015 Time: 6.30 p.m p.m. Name. Student No.. Section No. Instructors: Drs. Abdelkarim, Afrousheh, Farhan, Guzman, Kokaj, Marafi, Pichler, Sharma and Vagenas. (Fundamental constants) k = N.m 2 / C o = C 2 / (N m 2 ) 0 = T.m/A e = C NA = g = 9.8 m/s 2 me= kg mp = kg 2 (Coulomb constant) (Permittivity of free space) (Premeability of free space) (Elementary unit of charge) (Avogadro s number) (Acceleration due to gravity) (Electron mass) (Proton mass) Prefixes of units m = 10-3 = 10-6 n = 10-9 p = k = 10 3 M = 10 6 G = 10 9 T = For use by Instructors only Prob Total Marks Ques Total Marks

PART I. Solve the following problems. Show your solutions in detail. 1. In the figure, a ring with radius R= 0.71 m lies in the YZ plane and carries a charge Q= 580 nc uniformly distributed over it.

2 PART I. Solve the following problems. Show your solutions in detail. 1. In the figure, a ring with radius R= 0.71 m lies in the YZ plane and carries a charge Q= 580 nc uniformly distributed over it. A point charge q is placed at the center of the ring. The electric field is zero at the point P the distance of which from the center is x = 0.73 m. Find the charge q. [5 points] + 2. A very large conducting plate lying in the XY plane carries charge with surface density 2σ. A second such plate lies above it in a parallel plane at z = 2 m. The surface charge density on the upper plate is -3σ. If σ = 8.85 nc/m 2, find located at z = 0.60 m. [4 points] at a point P on the z-axis 1

The electric fields at the ends of S have the magnitudes E 1 = 6000 V/m and E 2 = 1000 V/m. Find the net flux through S.

3 3. A nonuniform electric field is given by. The axis of a cylindrical surface S, 0.80 m long and 0.20 m in diameter, is aligned parallel to the x-axis. The electric fields at the ends of S have the magnitudes E 1 = 6000 V/m and E 2 = 1000 V/m. Find the net flux through S. [3 points] 4. A spherical conductor of radius R = 20 cm carries a charge Q = -10 μc. Calculate the work done by an external force in moving a point charge q = 5 nc from point b to point a as shown in the figure if r a = 4 m and r b = 2 m. [3 points] 2

4 5. A particle of mass 4 x Kg and charge q = 6 μc enters a region of uniform electric field of magnitude = (2 x 10 7 V/m) î at the right angles to the direction of the field and with the speed v 0 = 10 6 m/s as shown in the figure. Determine its coordinates (x,y) after 4 μs have elapsed. [4 points] 6. A uniformly charged rod of length L = 9 m lies along the positive X-axis with its left end at the distance of 1 m from the origin O. If λ = 2 nc/m, calculate the potential at O. Take the potential to be zero at infinity. [5 points] 3

5 7. In the figure q 1 = q 3 = 8 nc and q 2 = -10 nc. Find the net electric field E at the point P. [4 points] 8. The figure shows three charges q 1 = 6 µc, q 2 = - 4 µc and q 3 = 2 µc in the XY plane. Calculate the total electric potential energy of the system. [4 points] 4

6 Part II. Conceptual questions (each carries 1 point). Tick the best answer: 1. The figure shows two point charges q = 6μC and Q = -10 μc. In which of the regions X, Y, Z will there be a point at which the net electric field is zero? a. Only regions X and Z. b. Only region X. c. Only region Z d. Only region Y. q Q X Y Z 2. Three equal negative point charges are placed at three corners of a square of side d as shown in the figure. Which of the arrows represents the direction of the net electric field at point O? a. A b. B c. C d. D -q A D O d C B -q d -q 3. Two very large parallel plates are uniformly charged and a distance d apart. At the point P half way between the two plates the electric field has the magnitude E. If the separation is reduced to ½ d what will be the magnitude of the electric field at P? a. 4E b. 2E c. E d. E/2 4. A charged conducting spherical shell with net charge Q on its surface has a point charge q at its center. The electric field lines are as shown. We conclude that a. Q > -q b. Q > 0 c. Q < 0 d. Q = -q Q q 5

7 5. At all points on an arbitrary equipotential surface the electric field a. is perpendicular to the surface. b. is tangential to the surface. c. always points away from the surface. d. always points towards the surface. 6. Two charged particles have a potential energy 20 J. If the charge of one of the particles is doubled and the distance between them increased four times, the potential energy will have the value a. 40 J b. 80 J c. 10 J d. 20 J 7. Two spherical conductors of radii R 1 = 3R and R 2 = R, respectively, are connected by a conducting wire. At equilibrium the ratio Q 1 /Q 2 of their charges is: a. 3 b. 1/3 c. 1 d A conductor with a cavity has a charge of -9 nc. If a charge q = 4nC is placed inside the cavity, the net charge on the outer surface of the conductor will be: a. 13 nc b. -4 nc c. -5 nc d. 9 nc 6

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Downloaded from Question 1.1: What is the force between two small charged spheres having charges of 2 10 7 C and 3 10 7 C placed 30 cm apart in air? Repulsive force of magnitude 6 10 3 N Charge on the first sphere, q