Basic Properties of Electric Charge:

• The fundamental electric quantity is charge.
• Atoms are composed of charge carrying particles: electrons and protons, and neutral particles, neutrons.
• The smallest amount of charge that exists is carried by an electron and a proton.
• Basic Properties of Electric Charge:
  – Additivity: If a system contains two-point charges q1 and q2, the total charge of the system is obtained simply by adding algebraically q1 and q2, i.e., charges add up like real numbers or they are scalars like the mass of a body.
  – Charge is conserved: Total charge of the isolated system is always conserved.
  – Quantization: all free charges are integral multiples of a basic unit of charge denoted by e.

Coulomb Law:

Force between two-point charges varies inversely as the square of the distance between the charges and is directly proportional to the product of the
magnitude of the two charges and acted along the line joining the two charges.
– Thus, if two point charges q1 , q2 are separated by a distance r in vacuum, the magnitude of the force (F) between them is given by:

Electric Field:

• Charge q produces an electric field everywhere in the surrounding
• When another charge q is brought at some point P, the field there acts on it and produces a force.
• Units are newtons per coulomb, equivalent to volts per metre
• The electric field produced by the charge q at a point r is given as:

Current:

• Current is rate of flow of negatively-charged particles, called electrons, through a predetermined cross-sectional area in a conductor. Flow of electrons in an electric circuit leads to the establishment of current.
• Current always flows from positive to negative.
• Unit of Current is Ampere.
• Amp = C/sec

Voltage:

• A Voltage is the force applied to a conductor which causes electric current to flow.
• It is the work done in moving a positive charge of 1 coulomb from one terminal through an element to another terminal.
• The force required to make electricity flow through a conductor is called a difference in potential, electromotive force (emf), or more simply referred to as voltage.

Resistance:

• Resistance (also known as ohmic resistance or electrical resistance) is a measure of the opposition to current flow in an electrical circuit.
• The amount of resistance depends upon composition, length, cross-section and temperature of the resistive material.
• Resistance of a conductor increases with an increase of length or a decrease of cross section.
• Resistance is designated by the symbol R and unit is Ohm.
• V=IR

Electric Circuit:

• Interconnection of electrical elements linked together in a closed path so that an electric current may continuously flow.

Elements in Electric Circuit:

• Linear Elements: Elements which satisfy the principle of superposition and homogeneity theorem are Linear Elements.
  – If the principle of superposition is true, then the excitation i1 + i2 must produce a response v1 + v2
  – If principle of homogeneity is true, the response of the element must be kv2, for an excitation ki.
  – Network consisting of linear elements is known as Linear Circuit.
• Passive Circuit Elements: Elements which cannot supply any energy (voltage or current), can only absorb a positive or zero energy
  • Current enters at positive(+ve) & leaves at negative(-ve) terminal.
  • Examples of passive elements are resistors, capacitors and inductors.
  • Active Circuit Elements: Elements which supply energy to a circuit or is a source of energy.
  • Current is supplied from +ve terminal & enters at -ve terminal.
  • Examples: Voltage & Current sources
• Unilateral network: An Unilateral network is one whose properties or characteristics change with the direction.
  • An example of unilateral network is the semiconductor diode, which conducts only in one direction.
• Bilateral network: A bilateral network is one whose properties or characteristics are same in either direction.
  • For example, a transmission line is a bilateral network, because it can be made to perform the function equally well in either direction.

Electrical Energy:

• The electrical energy is the amount of charge q moved through voltage V in a time interval t.
• The voltage across an element is the work done in moving a positive charge of 1 coulomb from first terminal through the element to second
  terminal.
• Unit of energy Joule, KWh(Kilowatt hour)

Electrical Power:

• It is the time rate of change of energy.
• P=dw/dt
• P=VI (For DC)
• AC Power:
  • p=vi(instantaneous AC Power)
  • P = VI cos ϕ (Real Power/Active Power/Consumed Power)
  • Unit: Watt
  • Q = VI sin ϕ (Reactive Power/Imagine Power)
  • Unit: Volt Ampere Reactive (VAR)
  • S=VI* (Total Power)
    – Unit is Volt Ampere(VA)