Electric Circuits: Charge

Electric charge is a fundamental physical property that causes matter to experience a force within an electromagnetic field.
Charge is conserved. This principle, known as the law of conservation of charge, maintains that in an isolated system, the total charge always remains constant.
There are two types of charge - positive and negative. Similar charges repel while opposite charges attract.
The unit of electric charge is the coulomb (C).
An elementary charge, often denoted by e, is approximately 1.60 x 10^(-19) coulombs and represents the smallest amount of electric charge that can exist independently. This value is the magnitude of the charge of a proton or the negative of the charge of an electron.

The quantity of charge (Q) passing a given point in a circuit can be found using the equation Q = It where I is the current and t is the time.
A current of one ampere means that one coulomb of charge is flowing past a given point in the circuit every second.

Conductors are materials that allow electric charge to free flow. These typically have a low number of valence electrons which can easily move, resulting in electric charge flow.
Insulators are materials that do not allow the free flow of electric charge. These typically have a high number of valence electrons that are not free to move.
Semiconductors are typically materials that fall between conductors and insulators. They do not conduct as well as conductors but can conduct much better than insulators under certain conditions.
Some semiconductors can be manipulated to either conduct or insulate, making them useful in the manufacture of electronic devices, including diodes and transistors.

Objects can be charged by contact, known as conduction, or by being close to a charged object, known as induction.
When two different materials are rubbed together (like a balloon and a wool sweater), electrons are transferred from the less electronegative material to the more electronegative material. This results in one object gaining a net negative charge and the other a net positive charge, a process known as triboelectric charging.

An electric field is a region around a charged object where the charge can exert a force.
The electric field strength (E) at a point in space is defined as the force (F) experienced by a small positive test charge (q), divided by the magnitude of the charge itself, i.e., E = F/q.
The direction of an electric field is always directed in the direction that a positive test charge would move.
The line along which a positively charged particle would move, or a line that indicates the direction of the electric field at various points, is known as an electric field line.

Coulomb’s law describes the force between two charges and states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
Mathematically, it can be expressed as **F=k q1q2 /r^2** where F is the force, q1 and q2 are the two charges, r is the distance between the charges, and k is the electrostatic constant.