Download Date: 13/11/2005

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
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