Chapter 1: Electric Charges and Fields Assertion-Reason Questions | physics Class 12 CBSE

Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 1

Logic Check

Assertion (A): Like charges repel and unlike charges attract each other. Reason (R): There are exactly two types of electric charge in nature, termed positive and negative.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 2

Logic Check

Assertion (A): A nylon comb gets electrified on combing dry hair, but a metal spoon held in the hand does not retain charge when rubbed. Reason (R): Nylon is an insulator so charge stays localised, while metal is a conductor and charge leaks through the hand to earth.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 3

Logic Check

Assertion (A): The total charge of an isolated system is always conserved. Reason (R): Charge can be created or destroyed but only in equal and opposite pairs.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 4

Logic Check

Assertion (A): Electric charge is always an integral multiple of e = 1.6 × 10⁻¹⁹ C. Reason (R): Quantisation of charge was first experimentally demonstrated by Faraday.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 5

Logic Check

Assertion (A): At the macroscopic level, quantisation of electric charge can be ignored and charge can be treated as continuous. Reason (R): At macroscopic scales, the charges involved are enormously larger than e, so the discrete steps of size e are imperceptibly small.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 6

Logic Check

Assertion (A): The Coulomb force between two charges is unaffected by the presence of other nearby charges. Reason (R): This is a statement of the principle of superposition, which is an experimental fact.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 7

Logic Check

Assertion (A): The electrostatic force between two charges obeys Newton's third law. Reason (R): F₁₂ = −F₂₁ follows directly from the vector form of Coulomb's law when subscripts 1 and 2 are interchanged.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 8

Logic Check

Assertion (A): The electric field due to a charge Q is independent of the test charge q used to measure it. Reason (R): The force F on the test charge is proportional to q, so the ratio F/q (which defines E) is independent of q.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 9

Logic Check

Assertion (A): Two electric field lines can cross each other at a point where the field is very strong. Reason (R): At the point of crossing, the field would have two directions simultaneously, which is physically impossible.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 10

Logic Check

Assertion (A): Electrostatic field lines do not form closed loops. Reason (R): Electrostatic field lines start on positive charges and end on negative charges; they cannot return to their starting point.

Reasoning Options

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Assertion-Reason

Easy difficulty • Check the statement and reason

Easy

Question 11

Logic Check

Assertion (A): The electric flux through a closed surface is zero if the net charge inside is zero. Reason (R): By Gauss's law, φ = q_enc/ε₀; when q_enc = 0, the flux is necessarily zero.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 12

Logic Check

Assertion (A): The total electric flux through a closed Gaussian surface depends on the size and shape of the surface. Reason (R): Gauss's law states that the flux equals q_enc/ε₀, which depends only on the enclosed charge and not on the surface shape or size.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 13

Logic Check

Assertion (A): The electric field inside a uniformly charged thin spherical shell is zero. Reason (R): The Gaussian surface inside the shell encloses no charge, so by Gauss's law the flux and hence E are zero.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 14

Logic Check

Assertion (A): The electric field outside a uniformly charged spherical shell is the same as if all the charge were concentrated at its centre. Reason (R): For r > R, Gauss's law gives E = q/(4πε₀r²), identical to the field of a point charge q at the centre.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 15

Logic Check

Assertion (A): The electric field due to an infinite plane sheet of charge is independent of the distance from the sheet. Reason (R): The sheet is infinite, so field lines are parallel and do not diverge; the flux through any pillbox of any height is the same.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 16

Logic Check

Assertion (A): The electric field due to an infinitely long wire varies as 1/r, while that of a point charge varies as 1/r². Reason (R): For an infinite wire, the relevant Gaussian surface is a cylinder; the enclosing area grows as r (not r²), giving a slower fall-off of field strength.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 17

Logic Check

Assertion (A): The dipole moment vector points from the negative charge to the positive charge by convention. Reason (R): Benjamin Franklin named the charges positive and negative and defined this convention for the dipole moment direction.

Reasoning Options

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Assertion-Reason

Hard difficulty • Check the statement and reason

Hard

Question 18

Logic Check

Assertion (A): The electric field of a dipole at large distances falls off as 1/r³, not 1/r² as for a point charge. Reason (R): The dipole consists of two equal and opposite charges; their fields nearly cancel at large distances, leaving a small residual field that decreases faster with distance.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 19

Logic Check

Assertion (A): A dipole placed in a uniform electric field experiences only a torque and no net translational force. Reason (R): In a uniform field, the forces on +q and −q are equal in magnitude but opposite in direction, so they cancel.

Reasoning Options

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Assertion-Reason

Medium difficulty • Check the statement and reason

Medium

Question 20

Logic Check

Assertion (A): A dipole in a non-uniform electric field experiences both a torque and a net translational force. Reason (R): In a non-uniform field, the forces on +q and −q have different magnitudes (since E differs at their positions), resulting in a net force.

Reasoning Options

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Chapter sections

Chapter 1: Electric Charges and Fields | Assertion-Reason

Assertion (A): Like charges repel and unlike charges attract each other. Reason (R): There are exactly two types of electric charge in nature, termed positive and negative.

Assertion (A): A nylon comb gets electrified on combing dry hair, but a metal spoon held in the hand does not retain charge when rubbed. Reason (R): Nylon is an insulator so charge stays localised, while metal is a conductor and charge leaks through the hand to earth.

Assertion (A): The total charge of an isolated system is always conserved. Reason (R): Charge can be created or destroyed but only in equal and opposite pairs.

Assertion (A): Electric charge is always an integral multiple of e = 1.6 × 10⁻¹⁹ C. Reason (R): Quantisation of charge was first experimentally demonstrated by Faraday.

Assertion (A): At the macroscopic level, quantisation of electric charge can be ignored and charge can be treated as continuous. Reason (R): At macroscopic scales, the charges involved are enormously larger than e, so the discrete steps of size e are imperceptibly small.

Assertion (A): The Coulomb force between two charges is unaffected by the presence of other nearby charges. Reason (R): This is a statement of the principle of superposition, which is an experimental fact.

Assertion (A): The electrostatic force between two charges obeys Newton's third law. Reason (R): F₁₂ = −F₂₁ follows directly from the vector form of Coulomb's law when subscripts 1 and 2 are interchanged.

Assertion (A): The electric field due to a charge Q is independent of the test charge q used to measure it. Reason (R): The force F on the test charge is proportional to q, so the ratio F/q (which defines E) is independent of q.

Assertion (A): Two electric field lines can cross each other at a point where the field is very strong. Reason (R): At the point of crossing, the field would have two directions simultaneously, which is physically impossible.

Assertion (A): Electrostatic field lines do not form closed loops. Reason (R): Electrostatic field lines start on positive charges and end on negative charges; they cannot return to their starting point.

Assertion (A): The electric flux through a closed surface is zero if the net charge inside is zero. Reason (R): By Gauss's law, φ = q_enc/ε₀; when q_enc = 0, the flux is necessarily zero.

Assertion (A): The total electric flux through a closed Gaussian surface depends on the size and shape of the surface. Reason (R): Gauss's law states that the flux equals q_enc/ε₀, which depends only on the enclosed charge and not on the surface shape or size.

Assertion (A): The electric field inside a uniformly charged thin spherical shell is zero. Reason (R): The Gaussian surface inside the shell encloses no charge, so by Gauss's law the flux and hence E are zero.

Assertion (A): The electric field outside a uniformly charged spherical shell is the same as if all the charge were concentrated at its centre. Reason (R): For r > R, Gauss's law gives E = q/(4πε₀r²), identical to the field of a point charge q at the centre.

Assertion (A): The electric field due to an infinite plane sheet of charge is independent of the distance from the sheet. Reason (R): The sheet is infinite, so field lines are parallel and do not diverge; the flux through any pillbox of any height is the same.

Assertion (A): The electric field due to an infinitely long wire varies as 1/r, while that of a point charge varies as 1/r². Reason (R): For an infinite wire, the relevant Gaussian surface is a cylinder; the enclosing area grows as r (not r²), giving a slower fall-off of field strength.

Assertion (A): The dipole moment vector points from the negative charge to the positive charge by convention. Reason (R): Benjamin Franklin named the charges positive and negative and defined this convention for the dipole moment direction.

Assertion (A): The electric field of a dipole at large distances falls off as 1/r³, not 1/r² as for a point charge. Reason (R): The dipole consists of two equal and opposite charges; their fields nearly cancel at large distances, leaving a small residual field that decreases faster with distance.

Assertion (A): A dipole placed in a uniform electric field experiences only a torque and no net translational force. Reason (R): In a uniform field, the forces on +q and −q are equal in magnitude but opposite in direction, so they cancel.

Assertion (A): A dipole in a non-uniform electric field experiences both a torque and a net translational force. Reason (R): In a non-uniform field, the forces on +q and −q have different magnitudes (since E differs at their positions), resulting in a net force.

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