Charge is the quantity
of electricity responsible for electric
phenomena. It is one of the fundamental
physical quantities in electric circuit
Coulomb’s law is
the fundamental law of the electric force
between two stationary, charged particles.
It states that the force of electrostatic
attraction or repulsion is directly proportional
to the product of the two charges and inversely
proportional to the square of the distance
between them. Coulomb’s law may also
introduce another concept that is the electric
field intensity (E).
Current is the time rate
of change of electric charge passing through
a predetermined area.
Current density is the
measure of the amount of current flowing
through a unit area normal to the direction
of current flow.
A direct current (DC)
is a current of constant magnitude in time.
A sinusoidal current (AC)
is that varies sinusoidaly with time.
Frequency is the number
of times the direction of current changes
(and changes back) per second.
Voltage across an element
is the electrical pressure, measured in
i.e., the electromotive force (EMF), which
causes current to flow through an electric
Resistance is the most
common component in electric circuits. It
is used mainly to control current and voltage
within the circuit. It is measured in ohms.
A passive element, however,
is defined as an element that cannot supply
an average power that is greater than zero
over an infinite time interval.
Conductance is the ability
of an element to conduct electric current;
it is measured in mhos or siemens (S).
Ohm’s Law deals
with the relationship between voltage and
current in an ideal conductor. This relationship
states that the potential difference v across
a conductor of resistance R is proportional
to the current i through it.
Power is the time rate
of expending or absorbing energy, measured
in watts (W).
Passive sign convention is
satisfied when the current enters through
the positive terminal of an element and
p = +vi . If the current enters through
the negative terminal, then p = -vi.
Energy is the capacity
to do work. It is measured in joules (J).
An electric circuit or
electric network is an interconnection of
electrical elements linked together in a
closed path so that electric current may
A reference point is an
arbitrarily chosen point to which all other
points in the circuit are compared.
An open circuit is a circuit
element whose resistance approaches infinity
R = ) and accordingly no current can flow
in the circuit.
A short circuit is a circuit
that has very little or no resistance to
limit the flow of current.
A grounded circuit is
a path of current other than the intended
that is established to ground.
A source is a voltage
or current generator capable of supplying
electrical energy to a circuit.
Independent source is
a source in which the voltage is independent
of the current, or the current is independent
of the voltage. It is termed as active elements.
Dependent source is a
source for which either the source voltage
or current depends upon a voltage or current
elsewhere in the circuit. It is termed as
An active element is an
element that is capable of furnishing an
average power greater than zero to some
external devices, where the average is taken
over an infinite time interval.
Kirchhoff’s current law (KCL)
states that at any node in a circuit, the
current arriving is equal to the current
Kirchhoff’s voltage law (KVL)
states that the algebraic sum of the voltage
drops in any closed path in a circuit and
the electromotive forces in that path are
equal to zero.
The elements of a series circuit
are connected end to end; the same current
flows through its parts one after another.
A voltage divider is a
circuit that works on the principle that
the sum of the voltage drops across a series
circuit must equal the applied voltage.
Voltage dividers may be constructed to produce
any voltage desired.
The elements of a parallel circuit
are connected so that each component has
the same voltage across its terminals; the
current flow is divided among its parts.
A combination circuit
is a circuit that contains a combination
of both series and parallel elements.
Circuit analysis is the
process of solving a circuit in order to
determine voltages across, or the current
through the elements of the circuit.
The capacitor is a passive
component. It is defined as the ability
to store an electric charge.
An inductor is defined as the ability of
a coil (consisting of multiple turns of
wire wound in a helical geometry around
a core) to store magnetic energy, induce
a voltage in itself, and oppose changes
in current flowing through it.