Download Date: 13/11/2005

Islamic University of Gaza
Faculty of Engineering
Electrical & Computer Engineering Department
EELE 3330 Electromagnetic I
Mid-Term II Exam
December 8,2005
Instructor : Dr. Mohamed Ouda
T.A: Eng. Mohammed El-Absi
Exam Time: 9:00 – 11:00
Name
ID Number
Grade
Read the following:
 You have two hour for this exam.
 This exam is closed book and closed notes. An equation
sheet has been
provided for you as the last page of the
exam.
 There are 5 problems on this exam, you must complete all
of the problems.
Good Luck
Question 1 (22 Points)
Indicate whether of the following statements are TRUE or FALSE. Explain your
answers to tell that you are not guessing.
(1) where surfaces ρ=2 and z=1 intersect is a cylinder (
)
(2) the vector component of 6ax + 2ay – 3az along 3ax - 4ay is 1.2ax – 1.6ay (
)
(3) The potential difference between two points in an imperfect conductor is zero
(
)
(4) By saying that the electrostatic field is conservative, we mean that the work done in a closed
path inside the field is zero (
)
(5) Electric current flowing in a copper wire is an example of conduction current (
(6) Sea water has  r = 80. Its permittivity is 79
(
(7) In a linear dielectric, P varies linearly with E (
)
)
)
(8) The major effect of the electric field on a dielectric is the creation of dipole moment in the
direction opposite to electric field (
)
(9) For good dielectrics, relaxation time is very large (
)
(10) The capacitance of a capacitor filled by a linear dielectric is independent of the charge on
the plates but depend on the potential difference between the plates (
)
(11) A cylindrical resistor of radius 5.0 mm and length 2.0 cm is made of material that has a
resistivity of 3.5 × 10-5Ω.m . the current density when the power dissipation is 1.0 W is
2.65× 10-3 Am-2 (
)
2
Question 2 (14 Points)
A conducting sphere of radius 10 cm is centered at the origin and embedded in a
dielectric material with ε  2.5ε ο . If the sphere carries a surface charge of 4 nC/m2, find
E at (-3 cm, 4 cm, 12 cm).
3
Question 3 (18 Points)
Two homogeneous dielectric regions 1 ( ρ ≤ 4 cm) and 2 ( ρ ≥ 4 cm ) have dielectric
constants 3.5 and 1.5, respectively. If D2 = 12aρ – 6aφ + 9az nC/m2 , calculate:
a) E1 and D1.
b) P2 and ρPv2 .
c) The energy density for each region.
4
Question 4 (18 Points)
The cylindrical capacitor has inner and outer radii of 5mm and 15mm, respectively. If
V(ρ = 5mm) = 100 V and V(ρ = 15mm) = 0 V,  r  2 . Calculate:
a) V & E at ρ = 10 mm .
b) ρs on each plate.
c) The capacitance per unit length.
5
Question 5 (18 Points)
An infinite uniform line charge, ρL = 25 nC/m, lies along the line x=0 , z=1 m in free space.
The surface z=0 is a perfect conductor.
a) Find E at P(1,2,3).
b) Find V at P if V = 0 at the origion.
c) What is the maximum magnitude of ρs on the conducting plane?
6