PASSIVE ELEMENTS
A
passive component only absorbs energy or absorbs energy then later releases it.
Main three types of passive components are:
1.
Resistor
2.
Capacitor
3.
Inductor
·
RESISTANCE
Definition:
“The hindrance or opposition offered by the
atoms of a conductor in the flow of electric current is called Resistance.”
Or
“It is
a ratio of the potential difference to the current.”
Symbol:
Resistance is designated by the symbol R.
Unit:
The
unit of measurement for resistance is ohms .
Factors on which resistance depends:
The
amount of resistance depends upon
1.
Length
2. Cross-section
3. Temperature
4.
Nature
of the substances
OHM’S LAW DEFINES RESISTANCE:
In 19th century, German mathematician, George Simon Ohm gave
the following law: "Voltage across the conductor is
directly proportional to the electric current passes through a conductor."
V α I
V = I R
Relationship between current and voltage can be
represented as,
Figure 1 v-I relationship of an ideal resistor
OHM’S LAW TRIANGLE
There
is an easy way to remember which formula to use.
COMBINATION
OF RESISTANCES:
1.
Serial Combination:
·
It is
formed when any numbers of resistors are connected in a circuit end-to-end so
that there is only one path for current to flow
·
Current
is the same anywhere it is measured in a series circuit
Total
or equivalent resistance (Req) can be calculated as,
Req = R1 + R2
+ R3 +…………………
2.
Parallel
Combination:
·
It is
formed when two or more resistances are placed side-by-side so that current can
flow through more than one path.
·
The
total or equivalent resistance is always smaller than any individual resistance
·
Voltage
is the same anywhere it is measured in a parallel circuit
Total
or equivalent resistance (Req) can be calculated as,
Circuit Symbol:
Two ways are:
Units of
Measurement
Special
prefixes that are commonly used when dealing with values of resistance:
Prefix
|
Symbol
|
Decimal
|
1 kilo ohm
|
1 KΩ
|
1000 Ω
|
1 mega ohm
|
1 MΩ
|
1,000,000 Ω
|
COLOR
CODING:
SOME OF THE DIFFERENT TYPES OF RESISTORS USED
ARE:
·
Axial
·
Surface
mount
·
CAPACITOR
Capacitor
is made of two metal plates with separated by insulating material. When a
voltage is applied to the plates, electrons are forced onto one plate. The
plate with an excess of electrons is negatively charged. The plate with a
deficiency of electrons is positively charged.
Symbol: Capacitor is designated by the symbol C.
Unit: The unit of measurement for capacitor is Farad (F).
Factors on which capacitance depend:
The
amount of capacitor depends upon
1.
Area
of the plates
2. Distance between the plates
3.
Material
of the dielectric
Simple Capacitive
Circuit
In
the following circuit, initially the switch is open and no voltage is applied
to the
Capacitor
and when the switch is closed, potential across the capacitor will rise rapidly
at first, then more slowly as the maximum value is approached.
Combination of Capacitors:
1. Serial Combination:
·
It is
formed when any numbers of capacitors are connected in a circuit end-to-end so
that there is only one path for current to flow
·
The
total or equivalent capacitor is always smaller than the individual capacitor
·
Current
is the same anywhere it is measured in a series circuit
Total
or equivalent capacitance (Ceq) can be calculated as,
2. Parallel Combination:
·
It is
formed when two or more capacitors are placed side-by-side so that current can
flow through more than one path
·
The
total or equivalent capacitor is always larger than any individual capacitor
·
Voltage
is the same anywhere it is measured in a parallel circuit
Total
or equivalent resistance (Ceq) can be calculated as,
Ceq = C1 + C2
+ C3 +…………………
Circuit Symbol:
Two ways are:
·
INDUCTOR
Definition:
Inductance
is the property of an electric circuit that opposes any change in electric
current.
Inductance
opposes change in current flow.
Symbol:
Inductance is designated by the letter “L”.
Unit:
The
unit of measurement for inductance is the Henry
(H).
Expression:
The
relationship between the time varying voltage across an inductor L and time
varying current passing through it can be expressed as,
Factors
on which inductance depend:
The
amount of inductance depends upon
1. Number of turns in the coil
2.
Spacing
between the turns
3. Coil diameter
4. Core material
5. Type of winding
Examples:
Examples are:
1. Transformers
2.
Chokes
3.
Motors
Simple Inductive Circuit
If
an inductor is used, the current does not change as quickly. In the following
circuit, initially the switch is open and there is no current flow and when the
switch is closed, current will rise rapidly at first, then more slowly as the
maximum value is approached.
Circuit Symbol:
Two ways are:
Combination of Inductances:
1 Serial Combination:
·
It is
formed when any numbers of inductors are connected in a circuit end-to-end so
that there is only one path for current to flow
·
The
total or equivalent inductance is always larger than the individual inductance
·
Current
is the same anywhere it is measured in a series circuit
Total
or equivalent resistance (Leq) can be calculated as,
Leq = L1 + L2
+ L3 +…………………
2.
Parallel Combination:
·
It is
formed when two or more inductance are placed side-by-side so that current can
flow through more than one path
·
The
total or equivalent inductance is always smaller than any individual resistance
·
Voltage
is the same anywhere it is measured in a parallel circuit
Total or
equivalent resistance (Leq) can be calculated as,
