Class 12 Physics – Electric Charges and Fields (Chapter Summary)

19 question-and-answer flashcards covering definitions, laws, formulas, and constants from the Class 12 Physics chapter "Electric Charges and Fields".

What fundamental property of matter causes it to experience a force in an electric field?

Electric charge

What are the two types of electric charge?

Positive charge and negative charge

What is the interaction rule between like and unlike charges?

Like charges repel each other, while unlike charges attract each other.

What does quantization of electric charge state?

Electric charge exists in integral multiples of the elementary charge: q = n e, where e = 1.6 × 10⁻¹⁹ C and n is an integer.

State the law of conservation of electric charge.

The total electric charge in an isolated system remains constant.

What is meant by the additive nature of charge?

The total charge of a system equals the algebraic sum of the individual charges present.

State Coulomb’s law for the force between two point charges.

F = k |q₁ q₂| / r², where k = 9 × 10⁹ N·m²/C² and r is the separation between the charges.

What is the SI value of the Coulomb constant k?

k = 9 × 10⁹ N·m² C⁻²

What does the principle of superposition for electric forces state?

The net force on a given charge equals the vector sum of the individual forces exerted on it by all other charges.

Define electric field intensity and give its basic formula.

Electric field intensity (E) is the force per unit positive test charge: E = F / q.

Give the expression for the electric field due to a point charge.

E = k q / r², directed radially outward for positive q and inward for negative q.

List three key properties of electric field lines.

(i) They originate on positive charges and terminate on negative charges. (ii) They never intersect. (iii) The tangent to a field line at any point gives the direction of the electric field at that point.

What is an electric dipole?

A pair of equal and opposite charges separated by a small distance.

Write the expression for electric dipole moment.

p = q (2a), a vector directed from –q to +q.

Give the electric field of a dipole on (a) the axial line and (b) the equatorial line.

(a) Axial line: E = (1/4πϵ₀) (2p / r³) ; (b) Equatorial line: E = (1/4πϵ₀) (p / r³)

Define electric flux and provide its formula.

Electric flux (Φ) is the total number of electric field lines passing through a surface: Φ = E A cos θ.

State Gauss’s law in electrostatics.

The net electric flux through any closed surface equals the total charge enclosed divided by ϵ₀: ∬ E·dA = q_inside / ϵ₀.

What is the value of the permittivity of free space (ϵ₀)?

ϵ₀ = 8.85 × 10⁻¹² C² N⁻¹ m⁻²

How is the Coulomb constant k related to the permittivity of free space ϵ₀?

k = 1 / (4πϵ₀)