X marks the spot what is the net electric field at

5. X marks the spot. What is the net electric field at point
X?
"
1 -
√
2
# "
1 -
√
2
#
A.
kq
a 2 2
ˆ ı +
kq
a 2 2
ˆ 
B.
kq
a 2
"
1 +
√
2
2
#
ˆ ı +
kq
a 2
"
1 +
√
2
2
#
ˆ 
C.
kq
a 2
"
√
2
2
- 1
#
ˆ ı +
kq
a 2
"
√
2
2
- 1
#
ˆ 
D. zero
6. Charge on X. Which of the following statements is/are TRUE if another point charge - 2 q
is placed at point X?
A – 3

First Long Exam First Semester, AY 2015–2016 Physics 72
7. Mutual repulsion. Two electrons exert a force with magnitude F on each other. What will
be the new magnitude of this mutual force if their separation distance is halved?
For the next three items, consider two infinite charged sheets
perpendicular to each other whose cross-sections are as
shown. The sheet along the x -axis has a uniform charge den-
sity + σ while the sheet along the y -axis has - σ .
8. Ilocos. What is the net electric field in region I?
9. Central Luzon. What is the net electric field in region III?
A.
σ
2
0
(ˆ ı + ˆ  )
B.
σ
2
0
(ˆ ı - ˆ  )
C.
σ
2
0
( - ˆ ı + ˆ  )
D.
σ
2
0
( - ˆ ı - ˆ  )
10. Before Deadpoole. If a dipole with p = p (ˆ ı + ˆ  ) , p > 0 , is placed in region II, which of
the following will happen to the dipole?
11. Bingbong. Which of the following Gaussian surfaces is the most useful in calculating the
electric field due to this cylinder?

First Long Exam First Semester, AY 2015–2016 Physics 72
12. Inside. If the cylinder has a non-uniform volume charge density ρ ( r ) = ρ
1
r
2
, ρ
1
> 0 , what
is the electric field in the region r < a ?
0
r
4
0
r
2
0
r
2
0
r
13. Out. If the cylinder has a uniform volume charge density ρ = ρ
2
, ρ
2
> 0 , what is the
electric field in the region r > a ?
A.
ρ
2
0
r
B.
ρ
2
2
0
a
2
r
C.
ρ
2
3
0
a
3
r 2
D.
ρ
2
4
0
a
4
r 3