CBSE Class 12th Physics Electric Charges and Fields 100 MCQs

Physics – Electric Charges and Fields

Class 12 Physics (Chapter 1) • 100 Multiple Choice Questions

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Question 1

What is the SI unit of electric charge?

Correct Answer: Coulomb

Question 2

Quantization of charge implies that:

Correct Answer: Charge exists as an integral multiple of elementary charge e

Question 3

The value of elementary charge (e) is approximately:

Correct Answer: 1.6 × 10⁻¹⁹ C

Question 4

Coulomb's law is applicable for:

Correct Answer: Point charges at rest

Question 5

The force between two point charges placed in a vacuum at a distance r is given by F. If they are immersed in a medium of dielectric constant K, the new force becomes:

Correct Answer: F / K

Question 6

Permittivity of free space (ε₀) has the value:

Correct Answer: 8.854 × 10⁻¹² C²N⁻¹m⁻²

Question 7

Electric field intensity at a distance r from a point charge q is proportional to:

Correct Answer: 1/r²

Question 8

Electric field lines always begin on a _____ charge and end on a _____ charge.

Correct Answer: Positive, Negative

Question 9

Two electric field lines can never intersect each other because:

Correct Answer: There would be two directions of electric field at that point

Question 10

An electric dipole consists of two equal and opposite charges separated by a small distance:

Correct Answer: 2a

Question 11

Electric dipole moment is a vector quantity directed from:

Correct Answer: Negative charge to positive charge

Question 12

The SI unit of electric dipole moment is:

Correct Answer: Coulomb-meter (C m)

Question 13

Electric field intensity at an axial point of a short dipole at distance r varies as:

Correct Answer: 1/r³

Question 14

Electric field intensity at an equatorial point of a short dipole at distance r varies as:

Correct Answer: 1/r³

Question 15

When an electric dipole is placed in a uniform electric field, the net force experienced by it is:

Correct Answer: Zero

Question 16

Torque experienced by an electric dipole placed in a uniform electric field E at angle θ is:

Correct Answer: pE sinθ

Question 17

Potential energy of an electric dipole in a uniform electric field is given by:

Correct Answer: -p · E

Question 18

Gauss's law relates the electric flux through a closed surface to:

Correct Answer: Total charge enclosed by the surface

Question 19

According to Gauss's law, total electric flux through a closed surface is equal to:

Correct Answer: q / ε₀

Question 20

Electric flux is a:

Correct Answer: Scalar quantity

Question 21

The SI unit of electric flux is:

Correct Answer: N m²C⁻¹

Question 22

Electric field due to an infinitely long straight uniformly charged wire varies with distance r as:

Correct Answer: 1/r

Question 23

Electric field due to an infinite thin plane sheet of charge is:

Correct Answer: Independent of distance r

Question 24

Electric field inside a uniformly charged thin spherical shell is:

Correct Answer: Zero

Question 25

Electric field outside a charged spherical shell behaves as if the entire charge is concentrated at:

Correct Answer: Its center

Question 26

A glass rod rubbed with silk acquires:

Correct Answer: Positive charge

Question 27

An ebonite rod rubbed with fur acquires:

Correct Answer: Negative charge

Question 28

Charging by induction involves:

Correct Answer: No physical contact

Question 29

Surface charge density (σ) is defined as charge per unit:

Correct Answer: Area

Question 30

Linear charge density (λ) is defined as charge per unit:

Correct Answer: Length

Question 31

Volume charge density (ρ) is measured in:

Correct Answer: C/m³

Question 32

Force between two charges is F. If distance between them is halved, the force becomes:

Correct Answer: 4F

Question 33

Two identical metal spheres having charges +Q and -Q are brought in contact and then separated. The charge on each sphere will be:

Correct Answer: Zero

Question 34

The dielectric constant (K) of a metal is:

Correct Answer: Infinity

Question 35

The dielectric constant of a vacuum or air is taken as:

Correct Answer: 1

Question 36

If a body is charged, its mass:

Correct Answer: Slightly changes (increases or decreases)

Question 37

Which of the following charges is possible?

Correct Answer: 3.2 × 10⁻¹⁹ C

Question 38

Coulomb force is a:

Correct Answer: Conservative force

Question 39

Superposition principle of electric force states that total force on a charge is:

Correct Answer: Vector sum of forces exerted by all other charges

Question 40

Electric field inside a charged conductor is always:

Correct Answer: Zero

Question 41

Electric field lines at the surface of a charged conductor are always:

Correct Answer: Normal (perpendicular) to the surface

Question 42

A charge q is placed at the center of a cube of side a. The total electric flux through all faces of the cube is:

Correct Answer: q / ε₀

Question 43

Total electric flux through one face of a cube enclosing charge q at its center is:

Correct Answer: q / 6ε₀

Question 44

If the electric flux entering and leaving a closed surface are Φ₁ and Φ₂ respectively, the charge inside the surface is proportional to:

Correct Answer: Φ₂ - Φ₁

Question 45

When a soap bubble is given a positive charge, its size:

Correct Answer: Increases

Question 46

A neutral body can be attracted by a charged body due to:

Correct Answer: Electrostatic induction

Question 47

The force between two charges placed in air is F. If the space between them is completely filled with glass (K=6), the new force is:

Correct Answer: F / 6

Question 48

Which property is NOT satisfied by electric field lines?

Correct Answer: They form closed loops

Question 49

Electric dipole placed in a non-uniform electric field experiences:

Correct Answer: Both a net force and a torque

Question 50

Torque on a dipole is maximum when angle θ between p and E is:

Correct Answer: 90°

Question 51

Torque on a dipole is minimum (zero) when angle θ between p and E is:

Correct Answer: 0° or 180°

Question 52

Stable equilibrium of an electric dipole in an electric field occurs when angle θ is:

Correct Answer: 0°

Question 53

Unstable equilibrium of an electric dipole in an electric field occurs when angle θ is:

Correct Answer: 180°

Question 54

Electric flux through a closed surface depends on:

Correct Answer: Charge enclosed inside the surface

Question 55

If a closed surface encloses an electric dipole, the total electric flux through the surface is:

Correct Answer: Zero

Question 56

The electric field intensity due to a thin infinite plane sheet of charge is given by:

Correct Answer: σ / 2ε₀

Question 57

Electric field intensity just outside a charged conductor is:

Correct Answer: σ / ε₀

Question 58

A metallic spherical shell of radius R carries a charge Q. Electric potential inside the shell is:

Correct Answer: Constant and equal to that at the surface

Question 59

Coulomb's law in vector form accounts for:

Correct Answer: Both (a) and (b)

Question 60

Which material has the highest dielectric constant among these?

Correct Answer: Water

Question 61

If 1 coulomb charge is placed at 1 meter distance from another 1 coulomb charge in vacuum, the force between them is:

Correct Answer: 9 × 10⁹ N

Question 62

Point charges q₁ and q₂ are placed at distance r. The graph between force F and 1/r² is a:

Correct Answer: Straight line passing through origin

Question 63

The electric field inside a hollow charged metal sphere is zero. This can be proved using:

Correct Answer: Gauss's law

Question 64

The magnitude of electric field intensity E is related to electric potential V as:

Correct Answer: E = -dV/dr

Question 65

Electric lines of force contract lengthwise due to:

Correct Answer: Attraction between unlike charges

Question 66

Electric lines of force exert lateral pressure due to:

Correct Answer: Repulsion between like charges

Question 67

If charge on a body is doubled, its electric field at a point becomes:

Correct Answer: Doubled

Question 68

The electrostatic force is how many times stronger than gravitational force for two protons?

Correct Answer: 10³⁶ times

Question 69

Electrostatic shielding is based on the fact that electric field inside a conductor is:

Correct Answer: Zero

Question 70

Faraday cage works on the principle of:

Correct Answer: Electrostatic shielding

Question 71

A charge Q is divided into two parts q and Q-q. For maximum Coulomb force between them, q/Q must be:

Correct Answer: 1/2

Question 72

When a glass rod is rubbed with silk, the glass rod becomes positive because:

Correct Answer: It loses electrons

Question 73

The minimum amount of charge that can exist independently is:

Correct Answer: 1.6 × 10⁻¹⁹ C

Question 74

Electric field at the center of a uniformly charged ring is:

Correct Answer: Zero

Question 75

If an electric dipole is placed in a non-uniform electric field, it experiences:

Correct Answer: Force and torque both

Question 76

What is the angle between electric dipole moment and electric field when potential energy is minimum?

Correct Answer: 0°

Question 77

What is the angle between electric dipole moment and electric field when potential energy is maximum?

Correct Answer: 180°

Question 78

The work done in rotating an electric dipole from stable equilibrium to unstable equilibrium in a uniform electric field is:

Correct Answer: 2pE

Question 79

Gaussian surface is a:

Correct Answer: Imaginary closed surface

Question 80

For applying Gauss's law, the Gaussian surface should be chosen such that electric field is:

Correct Answer: Uniform and normal at every point on the surface

Question 81

Electric flux through a surface of area S placed parallel to uniform electric field E is:

Correct Answer: Zero

Question 82

Electric flux is maximum when angle between E and area vector S is:

Correct Answer: 0°

Question 83

If the radius of a charged spherical conductor is doubled while keeping charge constant, the potential at its surface becomes:

Correct Answer: Halved

Question 84

The unit of surface charge density is:

Correct Answer: C/m²

Question 85

The unit of linear charge density is:

Correct Answer: C/m

Question 86

Which of the following is a vector quantity?

Correct Answer: Electric field intensity

Question 87

Which of the following is a scalar quantity?

Correct Answer: Electric potential

Question 88

Electrostatic forces are central forces because:

Correct Answer: They act along the line joining the centers of two charges

Question 89

If a body gives out 10⁹ electrons every second, the time required to get a total charge of 1 C from it is approximately:

Correct Answer: 198 years

Question 90

Two point charges +4e and +e are fixed at a distance a apart. Where should a third charge q be placed on the line joining them so that it is in equilibrium?

Correct Answer: At distance 2a/3 from +4e

Question 91

Electric lines of force originate from positive charge and end at negative charge, showing that electric field is:

Correct Answer: Conservative

Question 92

What is the net charge on a charged capacitor?

Correct Answer: Zero

Question 93

When distance between two point charges is tripled, the electrostatic force between them becomes:

Correct Answer: 1/9 times

Question 94

The work done in moving a charge along an equipotential surface is:

Correct Answer: Zero

Question 95

An electric field line is a curve such that tangent to it at any point gives the direction of:

Correct Answer: Electric field intensity at that point

Question 96

The force per unit charge is known as:

Correct Answer: Electric field intensity

Question 97

Dimensional formula of electric field intensity is:

Correct Answer: [M L T⁻³ A⁻¹]

Question 98

Dimensional formula of permittivity of free space (ε₀) is:

Correct Answer: [M⁻¹ L⁻³ T⁴ A²]

Question 99

Dimensional formula of linear charge density (λ) is:

Correct Answer: [M⁰ L⁻¹ T⁰ A¹]

Question 100

Dimensional formula of surface charge density (σ) is:

Correct Answer: [M⁰ L⁻² T¹ A¹]