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Eastern Mediterranean University
Department of Physics
PHYS 102 – Second Midterm Examination
FALL SEMESTER (21.12.2004)
NUMBER
NAME SURNAME
INSTRUCTOR
GROUP
INSTRUCTIONS:
1) DO ALL THE QUESTIONS
2) TIME ALLOWED IS 90 MINUTES
3) READ CAREFULLY AND ANSWER ONLY WHAT IS ASKED IN THE
QUESTION.


F  q0 E

 
F  qv  B


 
F  qE  qv  B


F  ma

 
F  Id   B
f 

V  V fi    E  d s
dV  k



E  V
dq
r
dx
(x  b )
2
2
1

 ln x  x 2  b 2
  q
   E  dA  enclosed
0
U  qV
i
dE  k
dq
rˆ
r2

b
a

2
3
TOTAL
dx
b
 ln
x
a
Q1 Choose the best answer (Total marks = 5)
Gauss’s Law & Electric Potential (1 Mark each, Total = 4 marks)
Q1. An advantage of evaluating surface integrals related to Gauss’s law for charge distributions is:
A) the electric field is a constant on any surface
B) the electric field is of constant magnitude on certain surfaces
C) the charge is always on the surface
D) the flux is outward
Q1b. Volt per meter, V/m, are equivalent to Newton per coulomb? (Choose True or False!)
(A) TRUE
(B) FALSE
Q1c. The potential of a uniformly charged sphere is lowest at
A) the center of the sphere
B) the outside of the sphere
C) a distance from the sphere equal to its radius
D) infinity
Q1d. The electron volt is a unit for
A) potential
B) gradient
C) electron potential
D) energy
Magnetic Field Section
(1 Mark)
Q1e. The figure shown below has a magnetic force field vector on a wire of length
A)
F  I B(kˆ )
B)
C)
D)
F  I B( ˆj)
F  I B(kˆ )
F  I B(ˆi )
given by:
X
X
X
X
X
X
Bin
X
X
X
X
X
X
X
X
X
I
ĵ
k̂
î
Q2.
A small sphere carrying a charge Q is located at the center of a thick conducting spherical shell of
inner radius a and outer radius b carrying a net charge –2Q. Using Gauss’ law, find the electric field
at radius:
a) 0  r  a
(2 pts)
b) a  r  b
(1 pt)
c) r  b
(1 pt)
d) the induced charges on the inner and outer surfaces of the conducting shell
(1 pt)
Metal
b
a
Q
Free
space
Thick conducting shell
2Q
Q3.
A uniformly charged rod of density  and total charge Q is bent into a 3 4 -circle with a radius R
shown in the figure below.
a) Calculate the electrical potential at the pint P.
(3 pts)
b) Find the electric potential energy of a charge q if it is placed at the point P.
(2 pts)
y
Charged rod
R
P
x
z
x
Q4.
A magnetic field, B  (2.5ˆi  3.5ˆj) T , and an electric field, E  (3.2ˆi  3.0ˆj  2.5kˆ ) 103 V/m , act
together on a proton. At the time when the proton’s velocity is, v  (6.0kˆ ) 103 m/s , calculate:
(1.5 pts)
(a)
the electric force on the proton
(1.5 pts)
(b)
the magnetic force on the proton
(1 pts)
(c)
the net force on the proton (i.e., Lorentz force).

(1 pts)
(d)
The acceleration vector a of the proton.
(Take:
proton charge: q  1.6  10 19 C
mass: m  1.67  10 27 kg )