Courses

# CAPACITOR-Conceptual and NCERT Level Questions BM Sharma Notes | EduRev

## : CAPACITOR-Conceptual and NCERT Level Questions BM Sharma Notes | EduRev

``` Page 1

1
CAPACITOR
2CA-01
Conceptual and NCERT Level
1. Suppose the two plates of a capacitor have
different areas. When the capacitor is
charged by connecting it to a battery, do the
charges on the two plates have equal
magnitude, or may they be different? Explain
2. The charged plates of a capacitor attract each
other, so to pull the plates farther apart
requires work by some external force. What
becomes of the energy added by this work ?
3. The two plates of a capacitor are given
charges ±Q. The capacitor is then
disconnected from the charging device so
that the charges on the plates can’t change,
and the capacitor is immersed in a tank of
oil. Does the electric field between the plates
increase, decrease or stay the same ? Explain
your reasoning. How can this field be
measured ?
4. At which of the two
points, 1 or 2, of a
charged capacitor with
nonparallel plates is the
surface charge density
greater ?
5. In the figure shown, the
plate A has 100µ charge,
while the plate B has 60
µC charge.
(a) When both
switches are open, then
q
1
= _____________
q
2
= _____________
q
3
= _____________
q
4
= _____________
(b) When switch S
1
is closed only then
q
1
= ____________ q
2
= _____________
q
3
= ____________ q
4
= _____________
(c) When switch S
2
is also closed, then
q
1
= ____________ q
2
= _____________
q
3
= ____________ q
4
= _____________
6. A capacitor of capacitance C is charged to a
potential difference V from a cell and then
disconnected from it. A charge +Q is now
given to its positive plate. Find the potential
difference across the capacitor.
7. A parallel-plate vacuum capacitor with plate
area A and separation x has charges +Q and -
Q on its plates. The capacitor is disconnected
from the source of charge, so the charge on
each plate remains fixed.
(a) What is the total energy stored in the
capacitor ?
(b) The plates are pulled apart an additional
distance dx. What is the change in the
stored energy?
(c) If F is the force with which the plates
attract each other, then the change in
the stored energy must equal the  work
dW = F dx done in pulling the plates
apart. Find an expression for F.
(d) Explain why F is not equal to QE,
where E is the electric field between
the plates.
8. (a)  How many excess electrons must be
added to one plate and removed from
the other to give a 5.00 nF parallel
plate capacitor 25.0 J of stored  energy?
(b)  How could you modify the geometry
of this capacitor to get it to store 50.0
J of energy without changing the  charge
on its plates?
9.    A capacitor is connected across a battery.
(a) Why does each plate receive a charge
of exactly the same magnitude?
(b) Is this true even if the plates are of
different size? (Yes/No)
+
2
1
?
s
1
q
1
q
2
A
s
2
q
3
q
4
B
Page 2

1
CAPACITOR
2CA-01
Conceptual and NCERT Level
1. Suppose the two plates of a capacitor have
different areas. When the capacitor is
charged by connecting it to a battery, do the
charges on the two plates have equal
magnitude, or may they be different? Explain
2. The charged plates of a capacitor attract each
other, so to pull the plates farther apart
requires work by some external force. What
becomes of the energy added by this work ?
3. The two plates of a capacitor are given
charges ±Q. The capacitor is then
disconnected from the charging device so
that the charges on the plates can’t change,
and the capacitor is immersed in a tank of
oil. Does the electric field between the plates
increase, decrease or stay the same ? Explain
your reasoning. How can this field be
measured ?
4. At which of the two
points, 1 or 2, of a
charged capacitor with
nonparallel plates is the
surface charge density
greater ?
5. In the figure shown, the
plate A has 100µ charge,
while the plate B has 60
µC charge.
(a) When both
switches are open, then
q
1
= _____________
q
2
= _____________
q
3
= _____________
q
4
= _____________
(b) When switch S
1
is closed only then
q
1
= ____________ q
2
= _____________
q
3
= ____________ q
4
= _____________
(c) When switch S
2
is also closed, then
q
1
= ____________ q
2
= _____________
q
3
= ____________ q
4
= _____________
6. A capacitor of capacitance C is charged to a
potential difference V from a cell and then
disconnected from it. A charge +Q is now
given to its positive plate. Find the potential
difference across the capacitor.
7. A parallel-plate vacuum capacitor with plate
area A and separation x has charges +Q and -
Q on its plates. The capacitor is disconnected
from the source of charge, so the charge on
each plate remains fixed.
(a) What is the total energy stored in the
capacitor ?
(b) The plates are pulled apart an additional
distance dx. What is the change in the
stored energy?
(c) If F is the force with which the plates
attract each other, then the change in
the stored energy must equal the  work
dW = F dx done in pulling the plates
apart. Find an expression for F.
(d) Explain why F is not equal to QE,
where E is the electric field between
the plates.
8. (a)  How many excess electrons must be
added to one plate and removed from
the other to give a 5.00 nF parallel
plate capacitor 25.0 J of stored  energy?
(b)  How could you modify the geometry
of this capacitor to get it to store 50.0
J of energy without changing the  charge
on its plates?
9.    A capacitor is connected across a battery.
(a) Why does each plate receive a charge
of exactly the same magnitude?
(b) Is this true even if the plates are of
different size? (Yes/No)
+
2
1
?
s
1
q
1
q
2
A
s
2
q
3
q
4
B

2
2CA-01
CAPACITOR
Conceptual and NCERT Level
10. The plates of a plane capacitor are drawn
apart keeping them connected to a battery.
Next the same plates are drawn apart from
the same initial condition keeping battery
disconnected. In which case is more work
done ?
11. If a small charge q is moved along a closed
path in the field between the plates of a
parallel - plate capacitor, will any work be
done by the agent who moves the charge?
(Yes / No)
12. Which of the following changes to an ideal
parallel - plate capacitor connected to an
ideal battery will result in an increase in the
charge on the capacitor ?
(a) Decreasing the potential difference
across the plates
(b) Decreasing the area of the plates
(c) Decreasing the separation of the
plates
13. A parallel - plate capacitor is connected to an
ideal battery, which provides a fixed
potential difference. Originally the energy
stored in the capacitor is U
0
. If the distance
between the plates is doubled, then the new
energy stored in the capacitor will be……..
14. A capacitor has
square plates of side
a making an angle q
with each other as
shown in figure.
Show that the capacitance of this
arrangement is given by
2
0
1,
2
a a
C
tt
? ?
??
??
??
??

where d is the minimum separation between
the plates at one end. q is very small.
15. Each plate of a parallel plate air capacitor
has area S = 5 × 10
-3
m
2
and are d = 8.80 mm
apart. Plate A has positive change q
1
= +10
-10

C and plate B and change q
2
= +2 × 10
-10
C.
Calculate the energy supplied by a battery of
emf E = 10V When its positive terminal is
connected to plate A and negative terminal to
plate B. (Given ?
0
= 8.8 × 10
-12
)
16. A circuit has a section AB shown in figure.
5V
A B
C
1
=1 F ? C
2
=2 F ?
10V

The emf of the cell is 10 V and the capacitors
have capacitances C
1
= 1µF and C
2
= 2µF.
The potential difference V
AB
= 5V. Find the
charges on the capacitors.
17. Four identical
capacitor plates,
each of area A,
are arranged
such that
are a distance d apart. The plates are
connected to a source of emf V as shown in
the figure. Find the charge on plate 1 and
that on Plate 4.
18. N identical capacitors are connected in
parallel and then a potential difference of V
is applied to them. The potential difference
when these capacitors are reconnected in
series, their charges being left undisturbed ?
19. In the arrangement
shown, plate A & C are
connected together by a
conducting wire & plate
B is given a charge
equal to 60 µC. The ratio d
1
/ d
2
= 2.
q
1
= __________________
q
2
= __________________
q
3
= __________________
q
4
= __________________
q
5
= __________________
q
6
= __________________
?
a
a
t
+
V 1 2 3 4 5
A B C
q
1
q
2
q
3
q
4
q
5
d
1
d
2
```
Offer running on EduRev: Apply code STAYHOME200 to get INR 200 off on our premium plan EduRev Infinity!