Unit 2. Electricity and Magnetism
II. Conductors, capacitors, dielectrics
1.
Negative charge has been deposited on the irregular conducting solid shown above in cross section. What is the direction of the electric field at point
A
, ignoring any components of the field that point perpendicular to the page?
A
B
C
D
E
Questions 2 and 3 refer to the statement below:
Each square plate of a parallel plate capacitor has length
s
; the plates are separated by a distance
a
across a vacuum. The plates are directly connected to opposite sides of a battery of EMF
V
.
2.
Which of the following expressions gives the capacitance of this capacitor?
3.
Now the separation of the plates is doubled, as is the length of each side of each plate. This new capacitor is connected to the same battery. If the magnitude of the electric field inside the original capacitor was
E
, what is the magnitude of the electric field inside the new capacitor?
(1/2)
E
(1/4)
E
E
2
E
4
E
Questions 4 and 5 refer to the image below
A metal sphere of radius
R
1 carries charge +
Q
. A concentric spherical metal shell, of inner radius
R
2 and outer radius
R
3, carries charge +2
Q
.
4.
How much charge resides on the outer surface of the outer sphere?
-
Q
+
Q
+3
Q
+2
Q
-2
Q
5.
Which of the following graphs correctly represents the electric potential
V
as a function of the distance
r
from the center of the inner sphere?
A
B
C
D
6.
A parallel plate capacitor, consisting of two metal plates separated by a vacuum, is charged by connecting it to a battery of EMF
ε
. The battery is disconnected, and an insulating substance of dielectric constant
κ
is inserted between the plates. How does the voltage across the capacitor
V
and the charge stored on the capacitor
Q
change upon the dielectric's insertion?
V
increases,
Q
decreases
V
decreases,
Q
increases
V
does not change,
Q
increases
V
decreases,
Q
does not change
V
increases,
Q
does not change
7.
An uncharged spherical conducting shell is shown in the diagram above. It is desired to create an electric field at point
P
that points directly to the right. Either a positive or a negative point charge can be used to create this field. Placing a charge at which of the three labeled points could create the desired field?
X
or
Z
, but not
Y
.
X
only.
Z
only.
Y
or
Z
, but not
X
.
Y
only.
8.
Which of the following actions would cause the electrostatic energy stored in a parallel plate capacitor to double?
quadruple the potential difference between the two plates
quadruple the distance between the plates
double the distance between the plates
double the area of each plate
double the potential difference between the two plates
9.
Which of the following best explains why electronics corporations test their electromagnetic wave receivers (i.e. radios or cellphones) in a room enclosed by sheet of metal?
Electromagnetic waves cannot exist inside the room.
Electromagnetic waves generated from external sources cannot enter the room.
No charge can exist within the room.
The air inside the room cannot be ionized due to the metal sheet.
Magnetic fields cannot exist inside the room.
10.
Capacitor
C
1
is initially uncharged; capacitor
C
2
initially stores charge
Q
. The two capacitors are connected as shown above. After a long time, which of the following values must be the same?
I. The capacitance of each capacitor
II. The charge stored on each capacitor
III. The potential difference across each capacitor
None of the above
I only
II only
III only
II and III only
