Electric Charges and Fields - Vocabulary Flashcards (Video Notes)

Vocabulary-style flashcards covering core concepts from the video notes on Electric Charges and Fields.

Electrostatics

Branch of physics dealing with properties of electric charges at rest.

Electric Charge

Scalar quantity causing electrical and magnetic effects; excess electrons give negative charge, deficiency gives positive.

Conservation of Charge

Total charge of an isolated system remains constant.

Charge Quantization

Charges come in integral multiples of the elementary charge e (Q = N e; e ≈ 1.6×10^-19 C).

Charging by Friction

Charge transfer by rubbing; one body becomes positive, the other negative; charge is conserved.

Charging by Conduction

Charging by contact; charges redistribute until the connected conductors reach the same potential.

Conductor

Material with loosely bound outer electrons that are free to move; many free electrons.

Insulator (Dielectric)

Material with tightly bound electrons; no free charges to move.

Semiconductor

Material with free electrons but in small numbers; conductivity between conductor and insulator.

Grounding (Earthing)

Connecting a conductor to Earth; enables electron transfer to/from Earth, used in induction.

Induction (Charging by Induction)

Charging a body without direct contact by bringing a charged object nearby and rearranging charges; induced charge is opposite to inducing charge.

Induced Charge

Charge that appears on an object due to induction; its sign is opposite to the inducing charge.

Gold Leaf Electroscope

Device to detect charge: a brass rod with two thin gold leaves that diverge when charged.

Coulomb’s Law

F ∝ q1 q2 / r^2 for two stationary point charges; F along the line joining the charges.

Coulomb Constant (k)

k = 1/(4πε0) ≈ 8.99×10^9 N·m^2/C^2.

Permittivity of Free Space (ε0)

ε0 ≈ 8.85×10^-12 C^2/(N·m^2); constant in Coulomb’s law in vacuum.

Dielectric Constant (Relative Permittivity, εr or K)

Ratio ε/ε0; εr = K; measures how a medium reduces electric field relative to vacuum.

Effect of Medium on Field

Electric field in a dielectric is reduced by the factor εr: E = E0/εr.

Superposition Principle (Electric Fields)

Net electric field is the vector sum of the fields due to individual charges.

Electric Field

Region around a charge where a test charge experiences a force; a vector field.

Electric Field due to a Point Charge

E = k q / r^2, directed along r̂ (away from positive charge, toward negative).

Electric Field due to an Infinite Line Charge

E = λ / (2π ε0 r), directed away from the line for positive λ.

Electric Field due to a Uniformly Charged Disc on its Axis

E(z) = (σ/(2ε0)) [1 − z/√(z^2+R^2)], along the axis; z is distance from disc.

Electric Field due to a Circular Ring on its Axis

E(x) = (k Q x)/(x^2+R^2)^(3/2); along the axis of the ring.

Electric Field due to an Infinite Plane Sheet

E = σ/(2ε0) on each side; field is uniform and perpendicular to the sheet.

Gauss’s Law

∮ E·dA = Q_enclosed / ε0; net flux through a closed surface equals enclosed charge divided by ε0.

Electric Flux

Φ_E = ∮ E·dA; for uniform E through a plane area Φ = E A cosθ.

Flux through a Closed Surface

Net flux through a closed surface equals the enclosed charge divided by ε0.

Electric Field Inside a Hollow Sphere

Inside hollow conducting sphere, E = 0; outside, E = kQ/r^2.

Electric Field Inside/Outside a Uniform Solid Sphere

Outside: E = kQ/r^2; Inside (r < R): E = kQ r / R^3 (for uniform volume charge density).

Dipole Moment (p)

p = q d; vector from negative to positive charge.

Electric Field of a Dipole on Axial Point

E_axial = (1/(4πε0)) (2p)/r^3, direction along the axis from negative to positive charges.

Electric Field of a Dipole on Equatorial Point

E_equatorial = (1/(4πε0)) (p)/r^3; direction opposite to dipole moment for equatorial position.

Torque on a Dipole in Uniform Electric Field

τ = p × E; magnitude τ = p E sinθ.

Potential Energy of a Dipole in a Field

U = −p·E; minimum when dipole aligns with the field.

Angular SHM of a Dipole in Uniform Field

For small angle, θ̈ ≈ −(pE/I) θ; period T = 2π√(I/(pE)).

Nonuniform Field on a Dipole

Force on a dipole in nonuniform field: F = (p·∇)E; torque τ = p×E.

Electric Field Lines (Faraday)

Imaginary curves whose tangent gives the direction of the electric field; lines originate from positive charges and end on negative charges; they do not cross.

Conservative Electric Field

In electrostatics, the field is conservative; line integrals depend only on endpoints; potential energy exists.

Electrostatics

Branch of physics dealing with properties of electric charges at rest.

Electric Charge

Scalar quantity causing electrical and magnetic effects; excess electrons give negative charge, deficiency gives positive.

Conservation of Charge

Total charge of an isolated system remains constant.

Charge Quantization

Charges come in integral multiples of the elementary charge e (Q = N e; e \approx 1.6 \times 10^{-19} C).

Charging by Friction

Charge transfer by rubbing; one body becomes positive, the other negative; charge is conserved.

Charging by Conduction

Charging by contact; charges redistribute until the connected conductors reach the same potential.

Conductor

Material with loosely bound outer electrons that are free to move; many free electrons.

Insulator (Dielectric)

Material with tightly bound electrons; no free charges to move.

Semiconductor

Material with free electrons but in small numbers; conductivity between conductor and insulator.

Grounding (Earthing)

Connecting a conductor to Earth; enables electron transfer to/from Earth, used in induction.

Induction (Charging by Induction)

Charging a body without direct contact by bringing a charged object nearby and rearranging charges; induced charge is opposite to inducing charge.

Induced Charge

Charge that appears on an object due to induction; its sign is opposite to the inducing charge.

Gold Leaf Electroscope

Device to detect charge: a brass rod with two thin gold leaves that diverge when charged.

Coulomb’s Law

F \propto q1 q2 / r^2 for two stationary point charges; F along the line joining the charges.

Coulomb Constant (k)

k = 1/(4 \pi \varepsilon_0) \approx 8.99 \times 10^9 N \cdot m^2/C^2.

Permittivity of Free Space ( \varepsilon_0 )

\varepsilon_0 \approx 8.85 \times 10^{-12} C^2/(N \cdot m^2); constant in Coulomb’s law in vacuum.

Dielectric Constant (Relative Permittivity, \varepsilon_r or K)

Ratio \varepsilon / \varepsilon0 ; \varepsilonr = K; measures how a medium reduces electric field relative to vacuum.

Effect of Medium on Field

Electric field in a dielectric is reduced by the factor \varepsilonr : E = E0 / \varepsilon_r .

Superposition Principle (Electric Fields)

Net electric field is the vector sum of the fields due to individual charges.

Electric Field

Region around a charge where a test charge experiences a force; a vector field.

Electric Field due to a Point Charge

E = k q / r^2, directed along \hat{r} (away from positive charge, toward negative).

Electric Field due to an Infinite Line Charge

E = \lambda / (2 \pi \varepsilon_0 r) , directed away from the line for positive \lambda .

Electric Field due to a Uniformly Charged Disc on its Axis

E(z) = (\sigma / (2 \varepsilon_0)) [1 - z / \sqrt{(z^2 + R^2)}] , along the axis; z is distance from disc.

Electric Field due to a Circular Ring on its Axis

E(x) = (k Q x) / (x^2 + R^2)^{3/2} ; along the axis of the ring.

Electric Field due to an Infinite Plane Sheet

E = \sigma / (2 \varepsilon_0) on each side; field is uniform and perpendicular to the sheet.

Gauss’s Law

\oint E \cdot dA = Q{enclosed} / \varepsilon0 ; net flux through a closed surface equals enclosed charge divided by \varepsilon_0 .

Electric Flux

\Phi_E = \oint E \cdot dA ; for uniform E through a plane area \Phi = E A \cos \theta .

Flux through a Closed Surface

Net flux through a closed surface equals the enclosed charge divided by \varepsilon_0 .

Electric Field Inside a Hollow Sphere

Inside hollow conducting sphere, E = 0; outside, E = kQ/r^2.

Electric Field Inside/Outside a Uniform Solid Sphere

Outside: E = kQ/r^2; Inside (r < R): E = kQ r / R^3 (for uniform volume charge density).

Dipole Moment (p)

p = q d; vector from negative to positive charge.

Electric Field of a Dipole on Axial Point

E{axial} = (1 / (4 \pi \varepsilon0)) (2p) / r^3 , direction along the axis from negative to positive charges.

Electric Field of a Dipole on Equatorial Point

E{equatorial} = (1 / (4 \pi \varepsilon0)) (p) / r^3 ; direction opposite to dipole moment for equatorial position.

Torque on a Dipole in Uniform Electric Field

\tau = p \times E ; magnitude \tau = p E \sin \theta .

Potential Energy of a Dipole in a Field

U = -p \cdot E ; minimum when dipole aligns with the field.

Angular SHM of a Dipole in Uniform Field

For small angle, \ddot{\theta} \approx -(pE/I) \theta ; period T = 2 \pi \sqrt{(I / (pE))} .

Nonuniform Field on a Dipole

Force on a dipole in nonuniform field: F = (p \cdot \nabla)E ; torque \tau = p \times E .

Electric Field Lines (Faraday)

Imaginary curves whose tangent gives the direction of the electric field; lines originate from positive charges and end on negative charges; they do not cross.

Conservative Electric Field

In electrostatics, the field is conservative; line integrals depend only on endpoints; potential energy exists.