INDIAN SCHOOL MUSCAT
Class : XII Physics Assignment - 2 (2014 -2015)
Electrostatic Potential And Capacitance
Section A Conceptual and application type Questions
1
2
A capacitor is charged with a battery and then its plate separation is increased without
disconnecting the battery. What will be the change in i) Charge stored in the capacitor
ii) Energy stored in the capacitor iii ) Potential difference across the plates of the
capacitor. iv) Electric field between the plates of the capacitor. (2007)
The given graph shows that variation of charge q versus potential difference V for two
capacitors A and B. The two capacitors have same plate separation but the plate area of
B is double than that of A. Which of the lines in the graph correspond to A and B ?
Justify. ( 2006)
q
3
4
5
6
V
If the plates of a charged capacitor be suddenly connected to each other by a wire , what will
happen ? ( 2006)
If a dielectric slab completely inserted between the parallel plates of a capacitor is replaced by a
metal slab how does its capacitance change ? 2006
What is the direction of electric field line at a point with respect to equipotential surface? Give
reason.
P
+
K1
K2
Q
K3
-
Two parallel plates P and Q are kept at a distance ‘d’ apart . Area of each plate is A. The space
between them is filled with three dielectric slabs of identical size having dielectric constants
K1,K2 ,and K3 respectively as shown in the figure. Calculate the effective capacitance of the
Electrostatic Potential W.S. 2/Class XII/ V VETRISELVAN
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arrangement. (2002)
Sketch a graph to show the dependence of a charge Q stored in a capacitor on the potential
difference V applied. From the graph drawn how will you calculate the capacitance C of the
capacitor and the energy U stored in the capacitor.(2000)
Calculate the capacitance of the arrangement of two parallel plates of area A separated by a
distance of d between them. K1 ,K2, and K3 are the dielectric constants of the three materials in
between the plates as in the figure.
d
kK2
2
d/2
d/2
K1K1
k3
A/2
9
10
d/2
A/2
If a dielectric slab of dielectric constant K is introduced between the plates of a parallel plate
capacitor completely ,how does the energy density of the capacitor change?
The following table shows the dimensions and medium between the plates of three capacitors
P, Q and R. Compare their capacitances.
s.no Capacitor
1
2
3
4
Area of plates
Separation
Medium between
between the plates
the plates
1
P
A
D
Medium of εr =4
2
Q
2A
D/2
air
3
R
2A
D
Medium of εr =2
Section B Numericals
Six charges of 5µC are placed at the corners of a regular hexagon of side 10cm calculate the
electric potential at the centre of the hexagon.
Calculate the potential difference that must be applied to produce an electric field , that can
accelerate an electron to 1/10 th of velocity of light?
A parallel plate capacitor of capacitance 100µF is charged to 200V. After disconnecting it from
the battery , using an insulated handle , the distance between the plates is doubled. Find the i)
capacitance ii) pd between the plates and the energy stored in the capacitor.( 2003)
A 12pF capacitor is connected to a 50 V battery. How much electrostatic energy is stored in the
capacitor?
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Capacitance of a capacitor changes from 5µF to 30µF by the introduction of a dielectric slab
in between its plates, calculate its dielectric constant.
Calculate the equivalent capacitance between the points a and b in Figure.
7
Two tiny spheres carrying charges 1.5µC and 2.5µC are located 30cm apart. Find the electric
potential and field at the midpoint of the line joining the two charges , and at a point 10cm
from its mid point in a plane normal to the line and passing through the mid point.
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9
10
Three capacitors each of capacitance 9pF are connected in series. What is the effective
capacitance of the combination? What is the Pd across each capacitor if the combination is
connected to a 120 V supply?
Three capacitors each of capacitance 3pF are connected in parallel. What is the effective
capacitance of the combination? What is the charge on each capacitor if the combination is
connected to a 120 V supply?
A parallel plate capacitor has plates of area 200cm2 and the separation between the plates
1mm.Calculate i ) the potential difference between the plates if 1nC charge is given to the
capacitor ii) with the same charge if the plate separation is increased to 2mm, what is the new
potential difference and iii) electric field between the plates.
11
Calculate the equivalent capacitance between the points A and B of the given circuit.
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When an electron moves from A to B along an electric field line in the figure , the electron
does 3.94 x 10-19 J of work on it. What are the electric potential differences.
i) VB -VA ii) VC–VA iii ) VC –VB
13
Two capacitors of unknown capacitances are connected in series and parallel. If the net
capacitances in the two combinations are 6μF and 25μF respectively,find their capacitances.
14
Calculate the capacitance of the capacitor and the charge on each plate of a parallel plate
capacitor with air between the plates of cross sectional area 6 x 10-3m2 separated by 3mm, if the
capacitor is connected to 100V supply.
Explain what would happen if in the same capacitor a mica sheet of K=6 were completely
inserted between the plates,i) while the voltage source remained connected ii) after the supply
was disconnected.
15
Calculate the capacitance of the capacitor C in the figure. The equivalent capacitance of the
combination between A and B is 15 μF .
A
20 μF
C
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