Electric Charges and Fields

Comprehensive vocabulary flashcards covering electric charges, properties of charge, methods of charging, Coulomb's Law, its vector form, characteristics, and limitations based on lecture notes.

Electric Charge

An intrinsic property of elementary particles (such as electrons and protons) of which all objects are made. It is a scalar quantity, denoted by "$q$", with the SI unit of Coulomb ($C$). Charge is a property, not an entity.

Fundamental Law of Electrostatics

Like charges repel each other ($+$ repels $+$, and $-$ repels $-$), while unlike charges attract each other ($+$ attracts $-$).

Elementary Charge Magnitudes

The charge on one electron ($1e^-$) is $-1.6 \times 10^{-19}\text{ }C$, the charge on one proton ($1p^+$) is $+1.6 \times 10^{-19}\text{ }C$, and the charge on one neutron is $\text{Zero}\text{ }C$.

Neutral Body

A body that possesses an equal number of positive and negative charges ($\text{net} = 0$), meaning it is electrically balanced rather than being without charge.

Metric Submultiples of Coulomb

Common unit prefixes used for electric charge: $1\text{ }mC = 10^{-3}\text{ }C$, $1\text{ }\mu C = 10^{-6}\text{ }C$, $1\text{ }nC = 10^{-9}\text{ }C$, and $1\text{ }pC = 10^{-12}\text{ }C$.

Additivity of Charge

A scalar property stating that if a system contains point charges $q_1, q_2, q_3$, the total charge of the system is the algebraic sum of the individual charges: $q = q_1 + q_2 + q_3$.

Quantization of Charge

The principle that electric charge always occurs as an integral multiple of the basic elementary charge $e$, represented by the formula $q = n e$, where $n = 0, \pm 1, \pm 2, \dots$.

Conservation of Charge

The law stating that the total charge of an isolated system remains constant; electric charge can neither be created nor destroyed, and can only be transferred from one body to another.

Invariance of Charge

The property that electric charge is independent of the frame of reference; the charge on a body does not vary with speed, unlike mass and time which change at speeds comparable to the speed of light.

Fields Produced by Moving and Accelerated Charges

A charge at rest produces only an electric field; a charge in uniform motion ($v = \text{Constant}$) produces both an electric field and a magnetic field; an accelerated charge produces an electric field ($\vec{E}$), a magnetic field ($\vec{B}$), and radiates energy as electromagnetic waves (E.M waves).

Mass Variation During Charging

When a body is charged positively, it loses electrons and its mass decreases. When a body is charged negatively, it gains electrons and its mass increases.

Charging by Friction (Rubbing)

A method of charging where two bodies are rubbed together, causing electrons to transfer from the body with the lower work function to the body with the higher work function. (For example, clouds become charged by friction.)

Triboelectric Pairs

Specific pairs of materials that develop characteristic charges when rubbed together: Glass rod ($+\text{ve}$) with Silk cloth ($-\text{ve}$); Woollen cloth ($+\text{ve}$) with Plastic objects or rubber shoe ($-\text{ve}$); Cat skin ($+\text{ve}$) with Ebonite rod ($-\text{ve}$); Dry hair ($+\text{ve}$) with Comb ($-\text{ve}$).

Charging by Conduction

The process of transferring electric charge between two bodies through direct physical contact.

Electrostatic Induction

The phenomenon of temporary electrification of a conductor in which opposite charges appear at its closer end and similar charges appear at its farthest end in the presence of a nearby charged body.

Electron Transfer Calculation ($q = -2 \times 10^{-7}\text{ }C$)

Using $q = n e$, rubbing polythene with wool to produce a charge of $-2 \times 10^{-7}\text{ }C$ results in the transfer of $n = \frac{2 \times 10^{-7}}{1.6 \times 10^{-19}} = 1.25 \times 10^{12}$ (or $12.5 \times 10^{11}$) electrons, where the mass of an electron is $m_e = 9.1 \times 10^{-31}\text{ }kg$.

Coulomb's Constant ($K$)

The proportionality constant in Coulomb's Law, having a numerical value of $K = 9 \times 10^9\text{ }N\,m^2\,C^{-2}$.

Coulomb's Law

The electrostatic force of attraction or repulsion between any two point charges at rest is directly proportional to the product of the magnitudes of the charges ($F \propto q_1 q_2$), inversely proportional to the square of the distance between them ($F \propto \frac{1}{r^2}$), and acts along the line joining the two charges: $F = \frac{K q_1 q_2}{r^2}$.

Vector Form of Coulomb's Law

Expressed as $\vec{F}_{12} = -\vec{F}_{21}$ with equal magnitudes $|\vec{F}_{12}| = |\vec{F}_{21}|$, demonstrating that the electrostatic interaction between two charges forms an action-reaction pair and validates Newton's Third Law.

Point Charge

A charged body whose physical size is much smaller than the separation distance between it and another body; characterized as "NOT SMALL; BUT LOOKS SMALL".

Central Force Property of Coulomb's Law

The electrostatic force acts strictly along the straight line joining the centres of the two charged bodies.

Characteristics of Coulomb's Force

Key properties include: it is valid for point charges, forms action-reaction pairs obeying Newton's Third Law, is a central force, obeys the inverse square law, depends on the intervening medium, is a conservative force (work done is path-independent), and is a long-range force operating from $10^{-15}\text{ }m$ to $10^{18}\text{ }m$.

Limitations of Coulomb's Law

Coulomb's Law is strictly valid only when: 1) charges are at rest, 2) charges are point charges, and 3) the separation distance is greater than the nuclear distance ($1\text{ }fm = 10^{-15}\text{ }m$).