Phys102 Term: 131 Online HW-Ch25-Lec03
Q1:
Two parallel-plate capacitors with the same plate separation but different capacitance are connected in parallel to a battery. Both capacitors are filled with air. The quantity that is NOT the same for both capacitors when they are fully charged is:
A.
potential difference
B.
energy density
C.
electric field between the plates
D.
charge on the positive plate
E.
dielectric constant
Ans:
D
Q2:
Figure shows a parallel-plate capacitor with a plate area A = 5.56 cm
2 and a separation d = 5.56 mm. The left half of the gap is filled with material of dielectric constant κ
1
=
7.00. The right half is filled with material of dielectric constant κ
2
= 12.0. What is the capacitance of this configuration?
(Give the answer in three significant figures and SI units)
Ans:
Parallel Combination
C eq
= C
1
+ C
2
= k
1
ε
0 d
�A2�
+ k
2
ε
0 d
�A2�
ε
0
�
A
2d�
(k
1
+ k
2
) = 8.41 × 10 −12 F
Q3:
A 2.0-nF parallel plate capacitor is charged using a 12-V battery. The battery is removed and a dielectric of dielectric constant
κ
= 3.5 is inserted, filling completely the space between the plates of the capacitor. What is the energy stored in the capacitor after inserting the dielectric? (Give the answer in two significant figures and SI units)
Ans:
Q i
= C i
. V i
= Q f
U f
=
=
Q f
2C f
2
=
2.0 × 10
1
2 C i
−9
2 V i
2 ×
× 144
2 × 3.5
1 kC i
=
C i
V i
2
2k
= 4.1 × 10 −8 J
KFUPM-Physics Department 1