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KENDRIYA VIDYALAYA SANGATHAN
AHMEDABAD REGION
OBJECTIVE TYPE QUESTIONS
SUB: PHYSICS CHAPTER: ELECTRIC CHARGES AND FIELDS CLASS: XII
MULTIPLE CHOICE QUESTIONS
- An electric dipole of length 2 cm is placed at an angle of 30º with an electric field 2 X
5
N/C. If the dipole experiences a torque of 8 X 10
Nm, the magnitude of either
charge of the dipole, is
A) 4 μC
B) 7 μC
C) 8 mC
D) 2mC
- A negatively charged object X is repelled by another charged object Y. However, an
object Z is attracted to object Y. Which of the following is the most possibility for the
object Z?
A) Positively charged only
B) Negatively charged only
C) Neutral or positively charged
D) Neutral or negatively charged
- The magnitude of electric field due to a point charge 2q, at distance r is E. Then the
magnitude of electric field due to a uniformly charged thin spherical shell of radius R
with total charge q at a distance r/2, (r >>R) will be
A)
𝑬
𝟒
B) 0
C) 2E
D) 4E
- A square sheet of side 'a' is lying parallel to XY plane at z = a. The electric field in the
region is
E =c z
2
k. The electric flux through the sheet is
A) a
4
c
B)
𝟏
𝟑
a
3
c
C)
𝟏
𝟑
a
4
c
D) 0
- Three charges q, - q and q 0 are placed as shown in figure. The magnitude of the net
force on the charge q 0 at point O is [k = 1/ 4πϵ 0 ]
A) 0
B)
𝟐𝒒𝟏𝒒𝟐
𝒂𝟐
C)
√𝟐𝒒𝟏𝒒𝟐
𝒂𝟐
D)
𝟏
√𝟐
𝒒𝟏𝒒𝟐
𝒂𝟐
- Four objects W, X, Y and Z, each with charge +q is held fixed at four points of a
square of side d as shown in the figure. Objects X and Z are on the midpoints of the
sides of the square. The electrostatic force exerted by object W to object X is F. Then
the magnitude of the force exerted by object W to Z is
A)
𝑭
𝟕
B)
𝑭
𝟓
C)
𝑭
𝟑
D)
𝑭
𝟐
- Three charges +Q, q, +Q are placed respectively, at distance 0, d/2 and d from the
origin, on the x-axis. If the net force experienced by +Q placed at x = 0 is zero, then
value of q is
A) +Q/
B) – Q/
C) +Q/
D) – Q/
- Two identical small conducting balls B 1
and B 2
are given - 7pC and +4pC charges
respectively. They brought in contact with a third identical ball B 3
and then
separated. If the final charge on each ball is - 2pC, the initial charge on B 3
was
- Two identical conducting spheres A and B, carry equal charge. They are separated
by a distance much larger than their diameters, and the force between them is F. A
third identical conducting sphere, C, is uncharged. Sphere C is first touched to A,
then to B, and then removed. As a result, the force between A and B would be equal
to
A) F
B) F/
C) 3F/
D) 3 F/
- Eight equal charges each +Q are kept at the corners of a cube. Net electric field at
the Centre of the cube.
A) kQ/r
2
B) 8 k Q/r
2
C) 2 kQ/r
2
D) Zero
- Two-point charges Q and – 3 Q are placed at some distance apart. If the electric field
at the location of Q is E , then at the locality of – 3 Q , it is
A) - E
B) E/
C) - 3E
D) - E/
- Two- point charges +4 q and + q are placed at a distance L apart. A third charge Q is
so placed that all the three charges are in equilibrium. Then location and magnitude
of third charge will be
A) At a distance L/3 from+4q charge, +4q/
B) At a distance L/3 from +4q charge, - 4q/
C) At a distance 2L/3 from +4q charge, - 4q/
D) At a distance 2L/3 from +4q charge, +4q/
- A drop of 10
kg water carries 10
C charge. What electric field should be applied
to balance its weight (assume g = 10 m / s
2
A) 10 V/m, Upwards
B) 10 V/m, Downward
C) 0.1 V/m, Downward
D) 0.1 V/m, upward
- A point charge placed at any point on the axis of an electric dipole at some large
distance experiences a force F****. The force acting on the point charge when it’s
distance from the dipole is doubled is
A) F
B) F/
C) F/
D) F/
- In a region of space, the electric field is in the x - direction and proportional to x , i.e. ,
E= E 0 x i. Consider an imaginary cubical volume of edge a , with its edges parallel
to the axes of
coordinates. The charge inside this cube is
A) Zero
B) ϵ 0
E
0
a
3
C) E 0 a
3
/ ϵ 0
D) ϵ 0
Ea
2
- ABC is a right - angled triangle in which AB = 3 m, BC = 4 m and angle B = 90
0
. The
three charges +15C, +12C and 20C are placed respectively on A, B and C. The force
acting on B is –
A) 125N
B) 35N
C) 25N
D) Zero
- Two equal charges are separated by a distance d. A third charge placed on a
perpendicular bisector at x distance, will experience maximum coulomb force when
A) x= d/ √
B) x=d/
C) x= d/2√𝟐
D) x= d/ √
ASSERTION/REASON TYPE QUESTIONS
- Assertion (A): In a non-uniform electric field, a dipole will have translatory as well as
rotatory motion.
Reason (R): In a non-uniform electric field, a dipole experiences a force as well as
torque.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is NOT the correct explanation of A
C) A is true but R is false
D) A is false and R is false
- Assertion (A): Electric lines of force cross each other.
Reason (R): The resultant electric field at a point is the superimposition of the
electric fields at that point.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is NOT the correct explanation of A
C) A is true but R is false
D) A is false and R is false
- Assertion (A): Using Gauss law, it is possible to find the electric field at any point.
Reason (R): Gauss law is applicable for any type of charge distribution.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is NOT the correct explanation of A
C) A is true but R is false
D) A is false and R is false
iii) Three charges +2q, - q and +3q are given. Two charges + 2q and - q are enclosed
with in a surface 'S'. What is the electric flux due to this configuration through the
surface 'S'?
A) 5q/2 ϵ 0
B) 3q/ ϵ 0
C) 4q/ ϵ 0
D) q/ ϵ 0
iv) SI unit of electric flux is
A) N
2
mC B) NmC
C) Nm
2
C D) Nm
C
- The electric field due to a charge configuration with total charge zero is not zero, but
for distances large compared to the size of the configuration, its field falls off faster
than 1/r², typical of the field due to a single charge. An electric dipole is the simplest
example of this fact. An electric dipole is a pair of equal and opposite charges +q and
- q separated by some distance 2a. Its dipole moment vector p has magnitude 2qa and
is in the direction of the dipole axis from - q to +q. The electric field of the pair of
charges can be found out from Coulomb's law and the superposition principle. The
magnitude and the direction of the dipole field depend not only on the distancer but
also on the angle between the position vector and the dipole moment p. In some
molecules, like H₂O, the centers of - ve charges and of +ve charges do not coincide.
So they have permanent dipole moment. Such molecules are called polar molecules.
i) What will be the value of electric field at the Centre of the electric dipole?
A) Zero
B) Equal to the electric field due to one charge at Centre
C) Twice the electric field due to one charge at Centre
D) Half the value of electric field due to one charge at Centre
ii) If r is the distance of a point from the Centre of a short dip dipole, then the electric
field intensity due
to the short dipole remains proportional to
A) r
2
B) r
3
C) r
D) r
iii) An electric dipole coincides on Z-axis and its midpoint is on origin of the coordinate
system. The electric field at an axial point at a distance z from origin is E, and electric
field at an equatorial point at a distance y from origin is E y
Here z = y >>a, so | Ez|/|Ey| is
equal to
A) 1 B) 4 C) 3 D) 2
iv) An electric dipole of moment p is placed in a uniform - electric field E The maximum
torque
experienced by the dipole is
A) pE B) p/E C) E/p D)
3pE
- Surface Charge Density. Surface charge density is defined as the charge per unit
surface area the
surface (Arial) charge symmetric distribution and follow Gauss law of electro statics
mathematical term of surface charge density σ=ΔQ/ΔS
Two large thin metal plates are parallel and close to each other. On their inner faces, the
plates have surface charge densities of opposite sign (± s). Having magnitude 8.8 × 10
-
12
cm
- 2
as shown here. The intensity of electrified at a point is E =σ/ε 0 and flux is
Φ=E.ΔS, where ΔS = 1 m
2
(unit arial plate)
i) Electric field in the outer region (I) of the first (A) plate is
(a) 1.7 × 10
- 22
N/C
(b) 1.1 × 10
- 12
V/m
(c) Zero
(d) 11 × 10
- 12
V/m
ii) Electric field in the outer region (III) of the second plate (B) is
(a) 1 N/C
(b) 0.1 V/m
(c) 0.5 N/C
(d) zero
iii) The ratio of E from left side of plate A at distance 1 cm and 2 m respectively is
(a) 1: 2
(b) 10: 2
(c) 1: 1
(d) 20: 1
iv) Electric field in the region (II) is
(a) 1 N/C
(b) 0.1 V/m
(c) 0.5 N/C
(d) 2 N/C
- When electric dipole is placed in uniform electric field, its two charges experience
equal and opposite forces, which cancel each other and hence net force on electric
dipole in uniform electric field is zero. However, these forces are not collinear, so
they give rise to some torque on the dipole. Since net force on electric dipole in
uniform electric field is zero, so no work is done in moving the electric dipole in
uniform electric field. However, some work is done in rotating the dipole against the
torque acting on it.
KENDRIYA VIDYALAYA SANGATHAN
AHMEDABAD REGION
OBJECTIVE TYPE QUESTIONS
SUB: PHYSICS CHAPTER: ELECTROSTATIC POTENTIAL AND
CAPACITANCE
CLASS : XII
MULTIPLE CHOICE QUESTIONS
- Electric potential varies with distance such that V(x) = ax - bx
3
; where a and b are constants.
Where will the electric field intensity be zero?
A) x =
𝑎
𝑏
B) x =
𝑎
3 𝑏
C) x = √
𝑎
𝑏
D) x = ±√
𝑎
3 𝑏
- The 3 charges →
𝑞
2
, - q,
𝑞
2
are placed along the x axis at x = 0, x = r, x = 2r respectively. Find
the resultant potential at a point A located at a distance y from charge q such that r << y.
A) V =
4 𝑞𝑟
2
4 πεoy
B) V =
𝑞𝑟
3
4 πεo𝑦
3
C) V =
𝑞𝑟
2
4 πεo𝑦
3
D) V =
𝑞𝑟
3
4 πεo𝑦
2
- Three capacitors C1, C2 and C3 are connected in a combination as shown below. Identify
the correct statement(s).
(i) The charge on capacitor C1 is greater than that on capacitor C2.
(ii) The charge on capacitor C1 is the same as that on capacitor C3.
(iii) The charge on capacitor C1 is 30 μC.
A) Only (i) is correct
B) Only (iii) is correct.
C) Both (i) and (iii) are correct.
D) Both (i) and (ii) are correct.
- An electron is introduced in a region of an electric field. The charge starts accelerating in the
direction opposite to that of the field. Which of the following statements is true?
A) The field does positive work on the electron and its potential energy increases.
B) The field does positive work on the electron and its potential energy decreases.
C) The field does negative work on the electron and its potential energy increases.
D) The field does negative work on the electron and its potential energy decreases.
- Given below are the representations of uniform electric and gravitational fields.
In fig (a), a positive charge q moves from A to B in the direction parallel to electric field
E. The charge-field system undergoes a change in its electrical potential energy.
In fig (b), a mass particle m moves from A to B in the direction parallel to gravitational
field g. The mass-field system undergoes a change in gravitational potential energy.
Identify the statement that correctly states the changes in the energies of the above two
systems.
A) The charge-field system loses electrical potential energy whereas the mass-field system
gains gravitational potential energy.
B) The charge-field system gains electrical potential energy whereas the mass-field system
loses gravitational potential energy.
C) Both the charge-field system and the mass-field system lose their respective potential
energies.
D) Both the charge-field system and the mass-field system gain their respective potential
energies.
D) W/
- The potential at a point 𝑥 meaasured in 𝜇m due to some charges situated on the X - axis is
given by V(𝑥) =
20
𝑥
2
− 4
volt. The electric field E at 𝑥 = 4 𝜇m is given by
A) 10/9 volt/ 𝜇m and in the positive X direction
B) 5/3 volt/ 𝜇m and in the negative X direction
C) 5/3 volt/ 𝜇m and in the positive X direction
D) 10/9 volt/ 𝜇m and in the negative X direction
- Three identical capacitors of capacitance C each, are connected in series and this
combination is connected in in parallel with one more identical capacitor. The capacitance of
the whole combination is:
A) 3 C
B) 3/C
C) 3C/
D) 4C/
- Two identical capacitors are joined in parallel, charged to a potential V, separated and then
connected in serirs, i.e. the positive plate of one is connected to negative of the other:
A) The charges on the free plates connected together are destroyed
B) The charges on the free plate are enhanced
C) The energy stored in the system increases
D) The potential difference between the free plates is 2V
- A parallel plate air capacitor has a capacitance C. when it is half filled with a dielectric of
dielectric constant 5, the percentage increase in the capacitance will be
A) 400 %
B) 66.6 %
C) 33.3 %
D) 200 %
- Three charges; 1 𝜇C, 2 𝜇C, 3 𝜇C are kept at vertices of an equilateral triangle of side 1 m. if
they are brought nearer so that they now form an equilateral triangle of side 0.5 m, then work
done is:
A) 11 J
B) 1.1 J
C) 0.01 J
D) 0.11 J
- Four point charges; Q, - q, 2q and 2Q are placed one at each corner of a square. The
relation between Q and q for which the potential at the centre of of the square is zero is
A) Q = - q
B) Q = - 1/q
C) Q = q
D) Q = 1/q
- The variation potential V with r & electric field E with r for a point charge is correctly shown in
the graphs
A)
B)
C)
D)
- A capacitor has some dielectric between its plates, and the capacitor is connected to a dc
source. The batter is now disconnected and then the dielectric is removed, then
A) Capacitance will increase
- An electric charge 10
𝜇C is placed at the origin (0, 0) of X – Y coordinate system. Two
points A and B are situated at (√ 2 , √ 2 ) and (2, 0) respectively. The potential difference
between the points A and B will be
A) 4.5 volts
B) 9 volts
C) 2 volts
D) Zero
ASSERTION/REASON TYPE QUESTIONS
- Assertion (A) : A thin uncharged metallic plate placed in between the two charged plates of
a capacitor results in an arrangement equivalent to two capacitors in a series combination.
The equivalent capacitance of this combination stays the same irrespective of the position
of the metallic plate in between the plates of the capacitor.
Reason (R) : The change in the position of the central metallic plate, results in the
decrease in plate separation of one capacitor that is compensated by the increase in plate
separation for the other.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true and R is not the correct explanation of A
C) A is true but R is false
D) A is false and R is also false
- Assertion (A) : The electric potential is constant everywhere inside a charged conductor
and is equal to its value at the surface.
Reason (R) : A constant work has to be done to move a test charge from the interior of a
charged conductor to its surface.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is not the correct explanation of A
C) A is true but R is false
D) A is false and R is also false
- Assertion (A): If the distance between parallel plates of a capacitor is halved and dielectric
constant is made three times, then the capacitance becomes 6 times.
Reason (R) : Capacitance of the capacitor does not depend upon the nature of the material.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is not the correct explanation of A
C) A is true but R is false
D) A is false and R is also false
- Assertion (A) : An electron has a higher potential energy when it is at a location associated
with a negative value of potential and has a lower potential energy when at a location
associated with a positive potential.
Reason (R) : Electrons move from a region of higher potential to a region of lower
potential.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is not the correct explanation of A
C) A is true but R is false
D) A is false and R is also false
- Assertion (A) :Capacity of a conductor is independent on the amount of charge on it.
Reason (R) : Capacitance depends on the dielectric constant of surrounding medium,shape
and size of the conductor.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is not the correct explanation of A
C) A is true but R is false
D) A is false and R is also false
- Assertion (A) :Two equipotential surfaces cannot cut each other.
Reason (R) : Two equipotential surfaces are parallel to each other.
A) Both A and R are true and R is the correct explanation of A
B) Both A and R are true but R is not the correct explanation of A
C) A is true but R is false
D) A is false and R is also false
CASE BASED QUESTIONS
- The surface on which all points have the same potential is called the equipotential surface.
On the equipotential surface, to move a charge from one point to another no work is
required. Equipotential Points: The same electric potential points on the electric field are
called equipotential points. The line or curve connecting the points is known as an
equipotential line. The surface on which the point lies is called the equipotential surface.
The volume in which the points are filled is known as an equipotential volume. In an
- The potential at any observation point P of a static electric field is defined as the work done
by the external agent ( or negative of work done by electrostatic field ) in slowly bringing a
unit positive point charge from infinity to the observation point. Figure shows the potential
variation along the line of charges. Two point charges Q1 and Q 2 lie along a line at a
distance from each other.
i) At which of the points 1, 2 and 3 is the electric field is zero.
(A) 1
(B) 2
(C) 3
(D) both (A) and (B)
ii) The signs of Q1 and Q 2 respectively are
(A) Positive and negative
(B) Negative and positive
(C) Positive and positive
(D) Negative and negative
iii) Which of the two charges Q1 and Q 2 is greater in magnitude?
(A) Q 2
(B) Q
1
(C) same
(D) can’t be determined
iv) Which of the following statement is not true?
(A) Electrostatic force is conservative force
(B) Potential energy of charge q at a point is the work done per unit charge in
bringing a charge from infinity.
(C) When two like charges lie infinite distance apart, their potential energy is zero.
(D) Both (A) and (C)
- A dielectric slab is a substance which does not allow the flow of charges through it but
permits them to exert electrostatic forces on one another.
When a dielectric slab is placed between the plates, the field E o
polarises the dielectric. This
induces charge - Qp on the upper surface and + Qp on the lower surface of the dielectric.
These induced charges set up a field Ep inside as shown in the figure.
i) In a parallel plate capacitor, the capacitance increases from 4 μF to 80 μF on introducing a
dielectric medium between the plates. What is the dielectric constant of the medium
(A) 10
(B) 20
(C) 50
(D) 100
ii) A parallel plate capacitor with air between the plates has a capacitance of 8 pF. The
separation between the plates is now reduced half and the space between them is filled
with a medium of dielectric constant 5.
Calculate the value of capacitance of the capacitor in second case.
(A) 8 pF
(B) 10 pF
(C) 80 pF
(D) 100 pF
iii) A dielectric introduced between the plates of a parallel plate capacitor
(A) decreases the electric field between the plates
(B) decreases the capacity of the capacitor
(C) increases the charge stored in the condenser
(D) increases the capacity of the condenser
iv) A parallel plate capacitor of capacitance 1 pF has separation between the plates is d. When
the distance of separation becomes 2d and wax of dielectric constant x is inserted in it the
capacitance becomes 2 pF. What is the value of x?
(A) 2
(B) 4
(C) 6
(D) 8
