Electric Charges and Fields – Vocabulary Flashcards

Vocabulary terms and concise definitions covering essential concepts from the lecture notes on Electric Charges and Fields.

Electric charge

A property of matter that causes objects to experience a force in an electric field; it is a scalar quantity that can be positive, negative, or zero.

Electrostatics

Branch of physics dealing with static electric charges, their forces, fields, and potentials.

Coulomb's Law

The force between two stationary point charges in vacuum is proportional to the product of the charges and inversely proportional to the square of the distance between them.

Permittivity of free space (ε0)

A constant that appears in Coulomb's law; ε0 ≈ 8.85×10−12 C²N−1m−2; relates electric field and charge in vacuum.

Coulomb constant (k)

Proportionality constant in Coulomb's law; k = 1/(4π ε0) ≈ 9×10^9 N m² C⁻².

Absolute permittivity (ε)

Permittivity of a medium; ε = κ ε0 where κ is the relative permittivity of the medium.

Relative permittivity (dielectric constant, κ/εr)

Ratio of the permittivity of a medium to ε0; a dimensionless quantity indicating how much the medium reduces the electric field.

Electric field (E)

A vector field that represents the force per unit positive test charge at each point in space.

Electric field intensity

Another term for the electric field vector E; measured as force per unit charge.

Conductor

A material in which electric charges move freely; allows charge to flow easily.

Insulator (dielectric)

A material that does not conduct electricity well; resists the flow of electric charges.

Dielectric

An insulating material used to increase the capacitance of a system by reducing the effective electric field.

Gauss's law

The total electric flux through a closed surface equals the enclosed charge divided by ε0; ΦE = ∮ E·dA = Qenc/ε0.

Electric flux

The total number of electric field lines passing through a surface; ΦE = ∮ E·dA.

Gaussian surface

A closed, imaginary surface used in applying Gauss's law to exploit symmetry.

Electric field lines

Imaginary lines showing the direction of the electric field; start on positive charges and end on negative ones, do not intersect.

Charging by induction

Charging a neutral body by bringing a charged body near it without direct contact, causing charge rearrangement.

Charging by contact (conduction)

Charging a body by physical contact so charges are transferred between bodies.

Charging by friction (triboelectric effect)

Charging by rubbing two insulators or materials, transferring electrons and creating opposite charges on each.

Quantisation of electric charge

Electric charge exists only in integral multiples of the elementary charge e.

Elementary charge (e)

The magnitude of the charge of a single electron (≈ 1.6×10⁻¹⁹ C); basic unit of charge.

Additive nature of electric charge

Total charge in a system is the algebraic sum of the individual charges.

Conservation of electric charge

In any process, the net electric charge of an isolated system remains constant.

Solid angle/Surface charge density (σ)

Charge per unit area on a surface; units C/m².

Linear charge density (λ)

Charge per unit length on a line of charge; units C/m.

Volume charge density (ρ)

Charge per unit volume; units C/m³.

Electric dipole

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

Dipole moment (p)

p = q × d (charge times separation); a vector quantity pointing from negative to positive charge.

Axial line (dipole)

Line along the axis of the dipole; electric field strength has a specific form along this axis.

Equatorial line (dipole)

Line perpendicular to the axis of the dipole through its centre; the dipole field has a characteristic form here.

Torque on a dipole in a uniform field

τ = p × E = pE sinθ; torque tends to align the dipole with the field.

Work done in rotating a dipole

W = pE (cosθ1 − cosθ2); work required to rotate the dipole between orientations.

Electric potential energy of a dipole

U = −pE cosθ; energy associated with the orientation of a dipole in a field.

Electric dipole field (axial line)

Field on the axis of a dipole, often expressed as E ∝ p/r³.

Electric field due to a system of charges (superposition)

The net field is the vector sum of the fields due to each charge.

Polar molecule

Molecule with permanent dipole moment due to uneven charge distribution (e.g., H2O).

Electric field due to a point charge

E = kq/r², directed radially away from positive and toward negative.

Electric field magnitude (NC)

Unit of electric field is N/C (newtons per coulomb).

Electric flux density (D)

Often used in media; D = εE; related to permittivity of the medium.

Electric shielding (electrostatic shielding)

Conductor shields interior from external electric fields; field inside is zero.

Faraday cage

An enclosure of conducting material that blocks external static and low-frequency electric fields.

Cylindrical/planar/line charge fields

Specific field expressions for line, plane, and cylindrical charge distributions (special cases of Gauss's law).