# MCQs For NCERT Class 12 Physics Chapter 1 Electric Charges and Fields

Please refer to the MCQ Questions for Class 12 Physics Chapter 1 Electric Charges and Fields with Answers. The following Electric Charges and Fields Class 12 Physics MCQ Questions have been designed based on the latest syllabus and examination pattern for Class 12. Our experts have designed MCQ Questions for Class 12 Physics with Answers for all chapters in your NCERT Class 12 Physics book.

## Electric Charges and Fields Class 12 MCQ Questions with Answers

See below Electric Charges and Fields Class 12 Physics MCQ Questions, solve the questions and compare your answers with the solutions provided below.

Question. Two point charges A and B, having charges +Q and –Q respectively, are placed at certain distance apart and force acting between them is F. If 25% charge of A is transferred to B, then force between the charges
becomes
(a) 4F/3
(b) F
(c) 9F/16
(d) 16F/9

C

Question. The electrostatic potential inside a charged spherical ball is given by f = ar2 + b where r is the distance from the centre a, b are constants. Then the charge density inside the ball is
(a) –6aε0r
(b) –24paε0
(c) –6aε0
(d) –24paε0r

C

Question. A hollow insulated conduction sphere is given a positive charge of 10 mC. What will be the electric field at the centre of the sphere if its radius is 2 m?
(a) Zero
(b) 5 mCm–2
(c) 20 mCm–2
(d) 8 mCm–2

A

Question. Suppose the charge of a proton and an electron differ slightly. One of them is –e, the other is (e + De). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then De is of the order of
[Given: mass of hydrogen mh = 1.67 × 10–27 kg]
(a) 10–23 C
(b) 10–37 C
(c) 10–47 C
(d) 10–20 C

B

Question. Which of the following pair of quantities do not have the same dimensions :
(b) Torque, kinetic energy
(c) Light year, time period
(d) Impedance, reactance

C

Question. Two identical charged spheres suspended from a common point by two massless strings of lengths l, are initially at a distance d (d < < l) apart because of their mutual repulsion. The charges begin to leak from both the spheres at a constant rate. As a result, the spheres approach each other with a velocity v.
Then v varies as a function of the distance x between the spheres, as
(a) v ∝ x–1/2
(b) v ∝ x–1
(c) v ∝ x1/2
(d) v ∝ x

A

Question. The potential at a point P due to an electric dipole is 1.8 × 105V. If P is at a distance of 50 cm apart from the centre O of the dipole and if CP makes an angle 60° with the positive side of the axial line of the dipole, what is the moment of the dipole?
(a) 10 C–m
(b) 10–3 C –m
(c) 10–4 C–m
(d) 10–5 C–m

D

Question. Two point charges +q and –q are held fixed at (–d, 0) and (d, 0) respectively of a x – y coordinate system. Then
(a) the electric field E at all points on the axis has the same direction
(b) work has to be done in bringing a test charge from ¥ to the orgin
(c) electric field at all points on y-axis is along x-axis
(d) the dipole moment is 2qd along the x-axis

C

Question. When air is replaced by a dielectric medium of constant K, the maximum force of attraction between two charges separated by a distance
(a) increases K times
(b) remains unchanged
(c) decreases K times
(d) increases K–1 times.

D

Question. A charge q is placed at the centre of the line joining two equal charges Q. The system of the three charges will be in equilibrium if q is equal to
(a) –Q/4
(b) Q/4
(c) –Q/2
(d) Q/2

A

Question. “Parsec” is the unit of :
(a) time
(b) distance
(c) frequency
(d) angular acceleration

B

Question. Point charges +4q, –q and +4q are kept on the X-axis at point x = 0, x = a and x = 2a respectively. Then
(a) only –q is in stable equilibrium
(b) all the charges are in stable equilibrium
(c) all of the charges are in unstable equilibrium
(d) none of the charges is in equilibrium.

C

Question. An electron falls from rest through a vertical distance h in a uniform and vertically upward directed electric field E. The direction of electric field is now reversed, keeping its magnitude the same. A proton is allowed to fall from rest in it through the same vertical distance h. The time of fall of the electron, in comparison to the time of fall of the proton is
(a) smaller
(b) 5 times greater
(c) 10 times greater
(d) equal

A

Question. A toy car with charge q moves on a frictionless horizontal plane surface under the influence of a uniform electric field vector E. Due to the force qEvector , its velocity increases from 0 to 6 m s–1 in one second duration. At that instant the direction of the field is reversed. The car continues to move for two more seconds under the influence of this field. The average velocity and the average speed of the toy car between 0 to 3 seconds are respectively
(a) 2 m s–1, 4 m s–1
(b) 1 m s–1, 3 m s–1
(c) 1 m s–1, 3.5 m s–1
(d) 1.5 m s–1, 3 m s–1

B

Question. A particle of mass m and charge q is placed at rest in a uniform electric field E and then released. The kinetic energy attained by the particle after moving a distance y is
(a) qEy
(b) qE2y
(c) qEy2
(d) q2Ey

A

Question. Which of the following pairs does not have similar dimensions ?
(a) tension and surface tension
(b) stress and pressure
(c) Planck’s constant and angular momentum
(d) angle and strain

A

Question. A charge Q is enclosed by a Gaussian spherical surface of radius R. If the radius is doubled, then the outward electric flux will
(a) increase four times
(b) be reduced to half
(c) remain the same
(d) be doubled

C

Question. A charge Q is situated at the corner of a cube, the electric flux passed through all the six faces of the cube is
(a) Q/6ε0
(b) Q/8ε0
(c) Q/ε0
(d) Q/2ε0

B

Question. A point charge + q is placed at the centre of a cube of side l. The electric flux emerging from the cube is
(a) 6ql2/ε0
(b) q/6l2ε0
(c) zero
(d) q/ε0

D

Question. Three point charges +q, –2q and +q are placed at points (x = 0, y = a, z = 0), (x = 0, y = 0, z = 0) and (x = a, y = 0, z = 0) respectively. The magnitude and direction of the electric dipole moment vector of this charge assembly are
(a) 2qa along the line joining points (x = 0, y = 0, z = 0) and (x = a, y = a, z = 0)
(b) qa along the line joining points (x = 0, y = 0,z = 0) and (x = a, y = a, z = 0)
(c) 2qa along + x direction
(d) 2qa along + y direction.

A

Question. A point Q lies on the perpendicular bisector of an electrical dipole of dipole moment p. If the distance of Q from the dipole is r (much larger than the size of the dipole), then the electric field at Q is proportional to
(a) p2 and r–3
(b) p and r–2
(c) p–1 and r–2
(d) p and r–3

D

Question. An electric dipole is placed at an angle of 30° with an electric field intensity 2 × 105 N C–1.
It experiences a torque equal to 4 N m. The charge on the dipole, if the dipole length is 2 cm, is
(a) 8 mC
(b) 2 mC
(c) 5 mC
(d) 7 mC

B

Question. Which of the following physical quantities do not have same dimensions?
(a) pressure and stress
(b) tension and surface tension
(c) strain and angle
(d) energy and work.

B

Question. What is the flux through a cube of side a if a point charge of q is at one of its corner?
(a) 2q/ε0
(b) q/8ε0
(c) q/ε0
(d) q/2ε0 . 6a2

B

Question. A hollow metal sphere of radius R is uniformly charged. The electric field due to the sphere at a distance r from the centre
(a) decreases as r increases for r < R and for r > R
(b) increases as r increases for r < R and for r > R
(c) zero as r increases for r < R, decreases as rincreases for r > R
(d) zero as r increases for r < R, increases as r increases for r > R

C

Question. The electric field at a distance 3R/2 R from the centre of a charged conducting spherical shell of radius R is E.   The electric field at a distance R/2from the centre of the sphere is
(a) zero
(b) E
(c) E/2
(d) E/3

A

Question. A hollow insulated conduction sphere is given a positive charge of 10 mC. What will be the electric field at the centre of the sphere if its radius is 2 metres ?
(a) 20 mC m–2
(b) 5 mC m–2
(c) zero
(d) 8 mC m–2

C

Question. A body can be negatively charged by :
(a) removing some neutrons from it
(b) giving excess electrons to it
(c) removing some protons from it
(d) removing some electrons from it

B

Question. The number of electrons for one coulomb of charge are:
(a) 6.25 × 1023
(b) 6.25 × 1021
(c) 6.25 × 1018
(d) 6.25 × 1019

C

Question. What is the electric flux associated with one of faces of a cube, when a charge (q) is enclosed in the cube ?
(a) 6q/ε0
(b) q/6ε0
(c) q/3ε0
(d) 3q/ε0

B

Question. The point charges Q and –2Q are placed at some distance apart. If the electric field at the location of Q is E. The electric field at the location of Q is E. The electric field at the location of –2Q will be
(a) – 3E/2
(b) – E
(c) – E/2
(d) -2E

C

Question. How many electrons make up a charge of 20 μC.
(a) 1.25 × 1014
(b) 2.23 × 1014
(c) 3.25 × 1014
(d) 5.25 × 1014

A

Question. Let Ea be the electric field due to a dipole in its axial plane distant l and Eq be the field in the equatorial plane distant l’, then the relation between Ea and Eq will be :
(a) Ea = 4Eq
(b) Eq = 2Ea
(c) Ea = 2Eq
(d) Eq = 3Ea

C

Question. A particle of mass 2g and charge 1mC is held at a distance of 1m from a fixed charge 1mC. If the particle is released it will be repelled. The speed of particle when it is at a distance of 10 metre from the fixed charge is
(a) 90 m/s
(b) 100 m/s
(c) 45 m/s
(d) 55 m/s

A

Question. A conducting sphere of radius 10 cm is charged with 10 μC. Another uncharged sphere of radius 20 cm is allowed to touch it for some time. After that if the spheres are separated, then surface density of charges on the spheres will be in the ratio of
(a) 1 : 1
(b) 2 : 1
(c) 1 : 3
(d) 4 : 1

B

Question. An electric dipole placed in a non-uniform electric field experiences :
(a) both, a torque and a net force
(b) only a force but no torque
(c) only a torque but no net force
(d) no torque and no net force

A

Question. Two infinitely long parallel conducting plates having surface charge densities +s and –s respectively, are separated by a small distance.
The medium between the plates is vacuum. If ε0 is the dielectric permittivity of vacuum then the electric field in the region between the plates is :
(a) 0 volt/m
(b) s/ 2ε0 volt/m
(c) s/ ε0 volt/m
(d) 2s / ε0 volt/m

C

Question. Two parallel large thin metal sheets have equal surface charge densities (s = 26.4 × 10–12 c/m2) of opposite signs. The electric field between these sheets is :
(a) 1.5 N/C
(b) 1.5´10-10N/C
(c) 3 N/C
(d) 3´10-10N/C

C

Question. Three charge q, Q and 4q are placed in a straight line of length l at points distant 0, 1/2 and l respectively from one end. In order to make the net froce on q zero, the charge Q must be equal to
(a) –q
(b) – 2q
(c) -q/2
(d) q

A

Question. A solid sphereical conductor of radius R has a spherical cavity of radius a (a < R) at its centre. A charge + Q is kept at the centre. The charge at the inner surface, outer and at a position r (a < r < R) are respectively
(a) + Q, – Q, 0
(b) – Q, + Q, 0
(c) 0, – Q, 0
(d) + Q , 0, 0

Ans

B

Question. A glass rod rubbed with silk is used to charge a gold leaf electroscope and the leaves are observed to diverge. The electroscope thus charged is exposed to X-rays for a short period. Then
(a) the divergence of leaves will not be affected
(b) the leaves will diverge further
(c) the leaves will collapse
(d) the leaves will melt

Ans

B

Question. A solid conducting sphere of radius a has a net positive charge 2Q. A conducting spherical shell of inner radius b and outer radius c is concentric with the solid sphere and has a net charge – Q. The surface charge density on the inner and outer surfaces of the spherical shell will be

Ans

A

Question. An uncharged sphere of metal is placed in between charged plates as shown. The lines of force look like

(a) A
(b) B
(c) C
(d) D

Ans

C

Question. If a charge q is placed at the centre of the line joining two equal charges Q such that the system is in equilibrium then the value of q is
(a) Q/2
(b) –Q/2
(c) Q/4
(d) –Q/4

Ans

D

Question. The electric intensity due to a dipole of length 10 cm and having a charge of 500 μC, at a point on the axis at a distance 20 cm from one of the charges in air, is
(a) 6.25 × 107 N/C
(b) 9.28 × 107 N/C
(c) 13.1 × 1011 N/C
(d) 20.5 × 107 N/C

Ans

A

Question. Two positive ions, each carrying a charge q, are separated by a distance d. If F is the force of repulsion between the ions, the number of electrons missing from each ion will be (e being the charge of an electron)

Ans

C

Question. Five charges q1, q2, q3, q4, and q5 are fixed at their positions as shown in Figure, S is a Gaussian surface. The Gauss’ law is given by ∫Eds = q/∈0 Which of the following statements is correct?

(a) E on the LHS of the above equation will have a contribution from q1, q5 and q1, q5 and q3 while q on the RHS will have a contribution from q2 and q4 only
(b) E on the LHS of the above equation will have a contribution from all charges while q on the RHS will have a contribution from q2 and q4 only
(c) E on the LHS of the above equation will have a contribution from all charges while q on the RHS will have a contribution from q1, q3 and q5.
(d) Both E on the LHS and q on the RHS will have contributions from q2 and q4 only

Question. A hemisphere is uniformely charged positively. The electric field at a point on a diameter away from the centre is directed
(a) perpendicular to the diameter
(b) parallel to the diameter
(c) at an angle tilted towards the diameter
(d) at an angle tilted away from the diameter

Ans

A

Ans

B

Question. A point charge + q is placed at a distance d from an isolated conducting plane. The field at a point P on the other side of the plane is
(a) directed perpendicular to the plane and away from the plane
(b) directed perpendicular to the plane but towards the plane
(c) directed radially away from the point charge
(d) directed radially towards the point charge.

Ans

A

Question. Two pith balls carrying equal charges are suspended from a common point by strings of equal length. The equilibrium separation between them is r. Now the strings are rigidly clamped at half the height. The equilibrium separation between the balls now become

Ans

A