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Download Date: 13/11/2005
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Islamic University of Gaza Faculty of Engineering Electrical & Computer Dept. Instructor : Dr. Mohamed Ouda T.A: Eng. Mohammed El-Absi Date: 13/11/2005 Time: 90 Minutes. Electromagnetic I EELE 3330 Mid-Term Exam Student Name: …………………………………… ID Number: ………………. Attempt All Questions. Question 1 (18 Points) Indicate whether of the following statements are TRUE or FALSE. Explain your answers to tell that you are not guessing. (1) A unit normal vector to the cone θ = 30° is ( ar + aφ ) ( ) (2) Gauss's Law can be used when charge distribution is symmetric or not ( (3) An equipotential surface (or line) is one on which potential equal zero ( ) ) (4) The Electric Flux Intensity is the force per unit charge when placed in the electric field ( ) (5) Electric Field Intensity is dependent on the medium in which the charge is placed as soon as Electric Flux Density ( ) (6) Electric potential is measured in Joules per Coulomb and is dependent of the path taken ( ) (7) Plane z=10 m carries charge 20 nC/m2 . The magnitude of electric field intensity at the origin is -360π V\m and the direction of electric field intensity is az ( ) (8) The electric flux density on a spherical surface r = b is the same for point charge Q located at the origin and for charge Q uniformly distributed on surface r = a (a < b) ( ) (9) An electric dipole is formed when two point charges of equal magnitude but opposite sign ( ) 1 Question 2 (18 Points) A Uniformly charged annulus (ρs = 20 nC/m2) with 5cm ≤ R ≤ 10 cm is placed in free space at z = 0 plane. Find a) Potential at P(0,0,3m). b) What point charge could be placed at the origin to cause D to be zero at P(0,0,3m)? Annulus 2 Question 3 (18 Points) Using two different methods Find the free charge enclosed within the region defined by 1<ρ<2 , 1<φ<2 (rad) , 1<z<2 , given that D = 15ρ 2sin(2 ) a 10 ρ 2cos(2 )a C/m 2 ρ 3 Question 4 (18 Points) Find the work required to move a point charge Q = 10 nC from point ( 2.5 , 0 , the point ( 10 , 90° , 60° ) in the field E = 20 r sin( ) a r 10 r cos( ) a θ V/m What is the potential difference between the two points? 4 5 3 ) to 2 Question 5 (18 Points) A Copper sphere of radius 4 cm carries a uniformly distributed total charge of 5 µC on its surface in free space. a) Use Gauss's law to find D external to the sphere. b) Calculate the total energy stored in the electrostatic field. With my best wishes 5 8.854 10 xdx x x x a 2 dx 2 a2 xdx 2 a 2 12 3/ 2 2 3/ 2 6 109 F /m 36 x2 a2 C x / a2 x2 a2 1 x a2 2 C C