Electric Charges & Fields Lecture Notes

Practice flashcards covering the fundamental concepts, laws, and definitions of electric charges and fields according to the lecture notes.

Coulomb's Law (Scalar form)

States that the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitude of the charges and inversely proportional to the square of the distance between them.

Coulomb Constant ($K$)

A constant in the electrostatic force formula that depends on the units and the medium; in vacuum, it is approximately k = rac{1}{4\pi\epsilon_0} = 9 \times 10^9\,N\,m^2\,C^{-2}.

Absolute permittivity of free space ($\epsilon_0$)

A physical constant representing the capability of vacuum to permit electric fields, with a value of $8.85 \times 10^{-12}\,C^2\,N^{-1}\,m^{-2}$.

Newtonian forces

A term for electrostatic forces because they obey Newton\'s 3rd Law, meaning $\mathbf{F}<em>{12} = -\mathbf{F}</em>{21}$.

Central forces

Forces that act only in a straight line between two charges.

Conservative forces

Forces where the work done depends only on initial and final positions; the notes characterize the equal and opposite nature of electrostatic forces as leading to this property.

Superposition Principle

States that when several charges are present, the total force on a given charge is equal to the vector sum of the forces exerted on it by all the other charges.

Relative Permittivity or Dielectric Constant ($k$)

The ratio of the electrostatic force between two charges in a vacuum ($F$) to the force between them in a given medium ($F_m$), expressed as $k = \frac{F}{F_m} = \frac{\epsilon}{\epsilon_0}$.

Linear charge density ($\lambda$)

The charge per unit length for a uniform distribution, defined as $\lambda = \frac{dq}{dl}$.

Surface charge density ($\sigma$)

The charge per unit surface area for a uniform distribution, defined as $\sigma = \frac{dq}{ds}$.

Volume charge density ($\rho$)

The charge per unit volume for a uniform distribution, defined as $\rho = \frac{dq}{dv}$.

Electric field intensity ($E$)

The force exerted by a source charge per unit positive test charge, where $\mathbf{E} = \lim_{q_0 \to 0} \frac{\mathbf{F}}{q_0}$. Its S.I. unit is $\text{N/C}$ or $\text{Volt/metre}$.

Electric Dipole

A pair of equal and opposite charges ($+q$ and $-q$) separated by a small distance.

Electric Dipole moment ($\mathbf{p}$)

A vector quantity defined as the product of either charge ($q$) and the distance between the two charges ($2l$), pointing from the negative charge to the positive charge ($\mathbf{p} = q \times 2\mathbf{l}$).

Torque ($\tau$)

The turning effect experienced by a dipole in a uniform electric field, given by $\tau = pE \sin(\theta)$ or in vector form $\mathbf{\tau} = \mathbf{p} \times \mathbf{E}$.

Electric field lines

Imaginary straight or curved lines such that the tangent at any point gives the direction of the electric field at 그 point.

Electric flux ($\phi$)

The total number of electric field lines passing through a surface perpendicularly, calculated as the product of the electric field and the surface area ($\phi = E \cdot S$).

Area Vector

A vector that is always directed perpendicularly outwards from the surface of a closed body.

Gauss\'s Law

States that the total electric flux through any closed surface is equal to $\frac{1}{\epsilon_0}$ times the total electric charge enclosed within that surface ($\phi = \frac{q}{\epsilon_0}$).

Gaussian surface

Any hypothetical closed surface enclosing a charge used for applying Gauss\'s Law.