An electrical circuit is
an interconnection of
elements. These circuit
elements can be
categorized into two
types, namely active
elements and passive
Passive elements do not
generate (convert from non-
electrical energy) any
electricity. They may either
consume energy (i.e. convert
from electrical form to a non-
electrical form such as heat or
light), or store energy (in
electromagnetic fields). For
Resistor, inductor and
An Active Circuit Element is a component in a circuit
which is capable of producing or generating energy.
[Producing energy actually means converting non-
electrical form of energy to an electrical form]. Active
circuit elements are thus sources of energy (or simply
sources) and can be categorized into voltage sources
and the current sources.
Active elements are classified into two types:
1. Independent sources
2. Dependent sources
For an independent voltage source (or current
source), the terminal voltage (or current) would
depend only on the loading and the internal source
quantity, but not on any other circuit variable.
Independent sources are further classified into two
1. Independent current sources
2. Independent voltage sources
A dependent voltage source (or current source) would have its
terminal voltage (or current) depend on another circuit quantity such
as a voltage or current. Thus four possibilities exist.
Voltage dependent (controlled) voltage source
Current dependent (controlled) voltage source
Voltage dependent (controlled) current source
Current dependent (controlled) current source.
Node:- A simple node is a junction where any two
elements are connected.
Junction:- A principle node or junction is a place
where more than two elements are connected.
Branch:- It is the section between two nodes in the
Loop:- Loop is a close path made by branches in
which current can flow. One loop may consist of
number of meshes.
Mesh:- It is the loop which have no other connected
Kirchhoff’s current law: It state that, algebraic or vector sum of all the current
meeting at a junction or node is zero.
∑ientering = ∑ioutgoing
Kirchhoff’s voltage law: Total potential rise in any closed path is equal to the
total potential drop.
∑V = ∑IR
If the physical conditions remains same, the voltage across the conductor is
directly proportional to the current flowing in the conductor.
where R is proportionality constant known as resistance of the conductor.
On the basis of presence or absence of source
On the basis of direction of current
On the basis of seprability
On the basis of linearity
Active source:- if a network consist of an energy
source then it is called an active network.
Passive source:- if a network doesn’t contained
any energy sources then it is known as passive
1.Bilateral network:- it is the network whose
characteristics of response does not depends the
direction of current through the various elements
2.Unilateral network:- it is the network whose
characteristics of response depends the direction of
current through the various elements in it.
1.Distributed network:- if the network elements
such as resistance, inductance, and capacitance are
not physically separated. Example- transmission
2.Lumped network:- if the network elements are
physically separated. Example- simple electrical
1. Linear network:- if the characteristics parameters such
as inductance, resistance, capacitance are remains
constant w.r.t. changing parameters like voltage and
current known as linear network.
2. non linear network:- if the characteristics parameters
are not remains constant with respect to changing
parameters are known as non- linear networks.
An ammeter is a measuring
instrument used to measure
the current in a circuit. Electric
currents are measured
in amperes (A), hence the name.
Instruments used to measure
smaller currents, in the mill ampere
or microampere range, are
designated as milliammeters or micro
ammeters. It is always connected in
series with circuit.
1.Moving coil ammeters:- It uses magnetic
deflection, where current passing through
a coil causes the coil to move in a magnetic
An electrodynamic movement uses an
electromagnet instead of the permanent
magnet of the moving coil. This instrument
can respond to both alternating and direct
current and also indicates true RMS for
3.Moving iron ammeters:- Moving
iron ammeters use a piece of iron which
moves when acted upon by the
electromagnetic force of a fixed coil of
A voltmeter is an instrument
used for measuring electrical
potential difference between
two points in an electric
circuit. It is always connected
parallel to the electrical
1.On the basis of nature of electric
current it is of two types AC and DC
2.On physical basis it is of two types
analogue and digital.
One kind has a needle, or "pointer",
that points to a number that tells the
number of volts. This is the kind of
voltmeter where one has to be careful
about making the positive and negative
connections correctly – if the wrong
connections are made, the voltmeter
can be damaged.
The second kind of voltmeter shows
the numbers in a "digital" way, just like
digital clocks and calculators. This kind
of voltmeter is not damaged from
"wrong" connections; instead, they
show a negative number.
wattmeter is an instrument
for measuring the electric
power (or the supply rate
of electrical energy)
in watts of any given circuit.
Wattmeter contain two coils:-
one is current coil and other
is pressure coil. Current coil
is connected in series while
pressure coil connected in
parallel with the electrical
1.DC wattmeter:- It uses dc current and voltage. The
result of this arrangement is that on a dc circuit,
the deflection of the needle is proportional to
both the current and the voltage, thus
conforming to the equation p=vi.
1.AC wattmeter:- it uses ac current ad voltage.
For AC power, current and voltage may not be
in phase, owing to the delaying effects of
circuit inductance or capacitance. On
an ac circuit the deflection is proportional to
the average instantaneous product of voltage
and current, thus measuring true
power, P=VI cos φ. Here, cosφ represents
the power factor which shows that the power
transmitted may be less than the apparent
power obtained by multiplying the readings of
a voltmeter and ammeter in the same circuit.
Transformers are used
to convert high voltage,
low current in to low
voltage, high current or
changing the frequency
of current. It works
upon the principle of
A transformer has three main parts:
laminated core, primary coil and
1.Laminated core- core is obtained by
piling a no. of laminated rectangular
strips of soft iron. Laminated strips
are insulated from each other by a
coating of varnish or insulating paint
for the prevention from loss of energy
by eddy currents.
2.Primary coil-the coil connected to
the input of a.c. Is called primary coil.
3.Secondary coil-coil through which
output is taken is called secondary
Step -up transformer: it
changes strong ac current at
low voltage into weak ac
current at high voltage.
Number of turns in secondary
coil is more than primary coil.
Step-down transformer: it
changes weak ac current at
high voltage into strong ac
current at low voltage. Number
of turns in primary coil is
greater than secondary coil.
1.Shell type:- when windings are
surrounded by the core, the
transformer is shell form. Shell
type transformers are popular
in Low voltage applications like
transformers used in electronic
circuits and power electronic
2.core type:- When windings
surround the core, the transformer
is core form. Core
type transformers are popular
in High voltage applications like
Distribution transformers, Power
transformers, and obviously auto