CBSE Class 12 Physics Quiz | CBSE Class 12 Physics Multiple Choice Questions(MCQs) & Answers

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Questions
1 Which of the following statements is not true about Gauss’s law?
A Gauss’s law is true for any closed surface.
B The term q on the right side side of Gauss’s law includes the sum of all charges enclosed by the surface.
C Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.
D Gauss’s law is based on the inverse square dependence on distance contained in the coulomb’s law

Answer: Gauss’s law is not much useful in calculating electrostatic field when the system has some symmetry.
2 The surface considered for Gauss’s law is called
A Closed surface
B Spherical surface
C Gaussian surface
D Plane surface

Answer: Gaussian surface
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3 Consider a region inside which, there are various types of charges but the total charge is zero. At points outside the region
A the electric field is necessarily zero.
B the electric field is due to the dipole moment of the charge distribution only.
C the dominant electric field is inversely pro-portional to r3, for large r (distance from ori-gin).
D the work done to move a charged particle along a closed path, away from the region will not be zero.

Answer: the dominant electric field is inversely pro-portional to r3, for large r (distance from ori-gin).
4 The unit of electric dipole moment is
A debye
B farad
C newton
D coulomb

Answer: debye
5 Electric field lines provide information about
A nature of charge
B direction
C field strength
D all of these

Answer: all of these
6 The force per unit charge is known as
A electric flux
B electric field
C electric potential
D electric current

Answer: electric field
7 SI unit of permittivity of free space is
A C2N-1 m-2
B C2N-1 m-2
C Farad
D None of these

Answer: C2N-1 m-2
8 Gauss’s law will be invalid if
A there is magnetic monopoles.
B the inverse square law is not exactly true.
C the velocity of light is not a universal constant.
D none of these.

Answer: the inverse square law is not exactly true.
9 The magnitude of electric field intensity E is such that, an electron placed in it would experience an electrical force equal to its weight is given by
A mge
B mg/e
C e/mg
D e²g/m²

Answer: mg/e
10 The electric field intensity due to an infinite cylinder of radius R and having charge q per unit length at a distance rir r(r > R) from its axis is
A directly proportional to r².
B directly proportional to r3.
C inversely proportional to r.
D inversely proportional to r².

Answer: inversely proportional to r.
11 Electric field at a point varies as r° for
A a plane infinite sheet of charge
B a line charge of infinite length
C an electric dipole
D a point charge

Answer: a plane infinite sheet of charge
12 The electric field inside a spherical shell of uniform surface charge density is
A directly proportional to the distance from the centre.
B zero.
C constant, less than zero.
D none of the these

Answer: zero.
13 A charge Q is divided into two parts of q and Q – q. If the coulomb repulsion between them when they are separated is to be maximum, the ratio of Q/q should be
A 2:1
B 1/4
C 1/2
D 4:1

Answer: 2:1
14 Two similar spheres having +Q and -Q charges are kept at a certain distance. F force acts between the two. If at the middle of two spheres, another similar sphere having +Q charge is kept, then it experiences a force in magnitude and direction as
A zero having no direction.
B 8F towards +Q charge.
C 8F towards -Q charge.
D 4F towards +Q charge.

Answer: 8F towards -Q charge.
15 In general, metallic ropes are suspended on the carriers taking inflammable materials. The reason is
A to control the speed of the carrier.
B to keep the centre of gravity of the carrier nearer to the earth.
C to keep the body of the carrier in contact with the earth.
D none of these.

Answer: to keep the body of the carrier in contact with the earth.
16 When a glass rod is rubbed with silk, it
A gains electrons from silk.
B gives electrons to silk.
C gains protons from silk.
D gives protons to silk.

Answer: gives electrons to silk.
17 Which of the following statement is correct? The electric field at a point is
A always continuous.
B continuous if there is a charge at that point.
C discontinuous only if there is a negative charge at that point.
D discontinuous if there is a charge at that point.

Answer: discontinuous if there is a charge at that point.
18 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 [NCERT Exemplar]
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.

Answer: directed perpendicular to the plane and away from the plane.
19 The SI unit of electric flux is
A N C-1 m-2
B N C m-2
C N C-1 m2
D N C-2 m2

Answer: N C-1 m2
20 A positively charged particle is released from rest in an uniform electric field. The electric potential energy of the charge [NCERT Exemplar]
A decreases because the charge moves along the electric field.
B decreases because the charge moves opposite to the electric field.
C remains a constant because the electric field is uniform.
D increases because the charge moves along the electric field.

Answer: decreases because the charge moves along the electric field.
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