Self- Learning Module Lab 02:Inductors

Electronic 1
AVT 1211

MIDTERM LABORATORY 1:

Inductors

Prepared by:
Rachelle R. Nocete

Page
Title Time

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 470.4 min

Course Learning Outcomes, Module Learning 3

Outcomes (MLO), Topic Learning Outcomes
(TLO)
Inductors 4

Inductance 6
You can do it Exercise

Energy storage 7

Inductor specifications 8

Inductor markings 9

Variable inductors 12

MIDTERM LABORATORY ACTIVITY 2 13

Reference 15

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Course Learning Outcomes (CLO)

Module Learning Outcomes (MLO)

Topic Learning Outcomes
(TLO)

CLO 1. Define
fundamental electrical
principles, electronic
principles and solve
related mathematical
problems.
CLO 3. Discuss, explain TLO1. Discuss the
and interpret electronic fundamental of
parts, specifications, MLO1.Explain what and Inductors
circuits, functions and how an indutors works
TLO2. Solve for induce
applications MLO 2.Distinguish types
of inductors and its voltage.TLO 3
CLO 4. Describe circuits ,
components and flow of specification Determined and discuss
voltage, current, MLO 3. Observe the the inductor’s
resistance and other inductors waveform in specification TLO4.
components an oscilloscope Observe the magnetic
CLO 5. Observe, reaction and wave
Examine and evaluate
forms of inductors in an
passive components of
electronics oscilloscope.
CLO 6. Differentiate DC
and AC circuits

Inductors

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Introductory Activity
Watch this video toget a an overview of what is an inductor and how it
works. Inductors Explained - The basics how inductors work working
principle-https://www.youtube.com/watch?v=KSylo01n5FY&t=340s - The
Engineering Mindset

Inductors provide us with a

means of storing electrical energy in
the form of a magnetic field. Typical
applications include chokes, filters
and (in conjunction with one or more
capacitors) frequency selective
circuits. The electrical characteristics
of an inductor are determined by a
number of factors including the material of the core (if any), the number of
turns and the physical dimensions of the coil. Fig. 2.35 shows the construction
of a typical toroidal inductor wound on a ferrite (high permeability) core.

In practice every coil comprises

both inductance (L) and a small
resistance (R). The circuit of Fig.
2.36 shows these as two discrete
components. In reality the
inductance and the resistance (we
often refer to this as a loss resistance because it’s something that we don’t
actually want) are both distributed throughout the component but it is
convenient to treat the inductance and resistance as separate components in
the analysis of the circuit.

To understand what happens

when a changing current flows through
an inductor, take a look at the circuit
shown in Fig. 2.37(a). If the switch is left
open, no current will flow and no
magnetic flux will be produced by the
inductor.

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 If the switch is closed, as
shown in Fig. 2.37(b), current will
begin to flow as energy is taken from
the supply in order to establish the
magnetic field. However, the change
in magnetic flux resulting from the
appearance of current creates a
voltage (an induced e.m.f.) across the
coil which opposes the applied e.m.f.
from the battery.

The induced e.m.f. results from

the changing flux and it effectively
prevents an instantaneous rise in
current in the circuit. Instead, the
current increases slowly to a
maximum at a rate which depends
upon the ratio of inductance (L) to
resistance (R) present in the circuit.
After a while, a steady state condition
will be reached in which the voltage
across the inductor will have decayed to zero and the current will have
reached a maximum value determined by the ratio of V to R (i.e. Ohm’s Law).
This is shown in Fig. 2.37(c).

If, after this steady state condition

has been achieved, the switch is
opened, as shown in Fig. 2.37(d), the
magnetic field will suddenly collapse
and the energy will be returned to
the circuit in the form of an induced
back e.m.f. which will appear across
the coil as the field collapses. For
large values of magnetic flux and
inductance this back e.m.f. can be
extremely large!

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Inductance

Inductance is the property of a coil which gives rise to the opposition to a

change in the value of current flowing in it. Any change in the current
applied to a coil/inductor will result in an induced voltage appearing across it.
The unit of inductance is the henry (H) and a coil is said to have an
inductance of 1 H if a voltage of 1 V is induced across it when a current
changing at the rate of 1 A/s is flowing in it.

The voltage induced across the terminals of an inductor will thus be

proportional to the product of the inductance (L) and the rate of change of
applied current. Hence:

e = −L × (rate of change of current)

Note that the minus sign indicates the polarity of the voltage, i.e. opposition
to the change.The rate of change of current is often represented by the
expression di/dt where di represents a very small change in current and dt
represents the corresponding small change in time. Using mathematical
notation to write this we arrive at:

You might like to compare this with the similar relationship that we obtained
for the current flowing in a capacitor shown in the previous module.

1 You can do it!

A current increases at a uniform rate from 2 A to 6 A in a period of 250 ms. If

this current is applied to an inductor of 600 mH, determine the voltage
induced.

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Energy storage

The energy stored in an inductor is proportional to the product of the

inductance and the square of the current flowing in it. Thus:

W = ½ L I2

where W is the energy (in joules), L is the capacitance (in henries) and I is the
current flowing in the inductor (in amperes).

Example 2.28

An inductor of 20 mH is required to store 2.5 J of energy. Determine the

current that must be applied.

Solution

The foregoing formula can be re-arranged to make I the subject as follows:

Inductance and physical dimensions

The inductance of an inductor depends upon the physical dimensions of the

inductor (e.g. the length and diameter of the winding), the number of turns
and the permeability of the material of the core. The inductance of an inductor
is given by:

Where

L is the inductance (in henries),

μ0 is the permeability of free space,

μr is the relative permeability of the magnetic core,

l is the mean length of the core (in metres) and

A is the crosssectional area of the core (in square metres).

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 https://study.com/academy/lesson/what-is-magnetic-permeability-
definition-examples.html

Example 2.29

An inductor of 100 mH is required. If a closed magnetic core of length 20 cm,

cross-sectional area 15 cm2and relative permeability 500 is available,
determine the number of turns required.

100 mH

20 cm

15 cm2.

500

Solution

First we must re-arrange the formula

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Inductor specifications

Inductor specifications normally include the value of inductance

(expressed in henries, millihenries or microhenries), the current rating (i.e. the
maximum current which can be continuously applied to the inductor under a
given set of conditions), and the accuracy or tolerance (quoted as the
maximum permissible percentage deviation from the marked value).

Other considerations may

include the temperature
coefficient of the inductance
(usually expressed in parts per
million, p.p.m., per unit
temperature change), the
stability of the inductor, the d.c.
resistance of the coil windings
(ideally zero), the Q-factor
(quality factor) of the coil and the recommended working frequency range.
Table 2.6 summarizes the properties of four common types of inductor. Some
typical small inductors are shown in Fig. 2.38. These have values of
inductance ranging from 15 μH to 1 mH.

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Inductor markings

As with capacitors, the vast majority of inductors use written markings to

indicate values, working current and tolerance. Some small inductors are
marked with coloured stripes to indicate their value and tolerance (in which
case the standard colour values are used and inductance is normally
expressed in microhenries).

Series and parallel combinations of inductors

In order to obtain a particular value of inductance, fixed inductors may be

arranged in either series or parallel, as shown in Figs 2.39 and 2.40. The
effective inductance of each of the series circuits shown in Fig. 2.39 is simply
equal to the sum of the individual inductances. So, for the circuit shown in
Fig. 2.39(a):

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Turning to the parallel inductors shown in Fig. 2.40, the reciprocal of the
effective inductance of each circuit is equal to the sum of the reciprocals of the
individual inductances. Hence, for Fig. 2.40(a):

In the former case, the formula can be more conveniently re-arranged as

follows:

You can remember this as the product of the two inductance values divided
by the sum of the two inductance values.

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Example 2.30

An inductance of 5 mH (rated at 2 A) is required. What parallel combination

of preferred value inductors will satisfy this requirement?

Solution

Two 10 mH inductors may be wired in parallel to provide an inductance of 5

mH as shown below:

Since the inductors are identical, the applied current will be shared equally
between them. Hence each inductor should have a current rating of 1 A.

Example 2.31

Determine the effective inductance of the circuit shown in Fig. 2.41.

Solution

The circuit can be progressively simplified as shown in Fig. 2.42. The stages in
this simplification are as follows:

(a) L1 and L2 are in series and they can be replaced by a single inductance (LA)
of (60 +60) = 120 mH.

(b) LA appears in parallel with L2. These two inductors can be replaced by a
single inductor (LB) of (120 × 120)/(120 + 120) = 60 mH.

(c) LB appears in series with L4. These two inductors can be replaced by a
single inductance (L) of (60 + 50) = 110 mH.

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Variable inductors

A ferrite-cored inductor can be made variable by moving its core in or out of

the former onto which the coil is wound. Many small inductors have threaded
ferrite cores to make this possible (see Fig. 2.43). Such inductors are often used
in radio and high-frequency applications where precise tuning is required.

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 MIDTERM LABORATORY ACTIVITY 2

_____________________

Signature over printed name

(Don’t need to write this in your notebook. Your signature over your printed name will suffice )

Name:
Date:
Course, Year and Section:

“As members of Academic Community, students are expected to

recognize and uphold standards of intellectual and academic integrity.
Philippine State College of Aeronautics assumes, as a basic and
minimum standard of conduct in academic matters, that
students should be honest and that they submit for credit only
the products of their own efforts.

______________________________
SIGNATURE OVER PRINTED NAME

ACTIVITY 1: INDUCTOR SPECS

Instruction: Research and choose a type of inductor. Include in your
research the specification of the inductor you have chosen.

a. Fill up the following information for the Inductor you have.

Inductor type:

Core Material

Inductance range

Typical DC resistance

Typical tolerance

Typical Q factor

Typical frequency range

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Typical application

b. Record yourself ( video) and tell us what your about the specific inductor
and the specifications of the inductor you have chosen.

ACTIVITY 2: INDUCTOR waveform

Watch this video https://www.youtube.com/watch?v=NgwXkUt3XxQ answer

the following.
1. How does an inductor store energy?
2. What is the characteristics of the change of current in an inductor?

3. What happen to the waveform when a 5mH in series of the circuit?

Describe the waveform as shown in the oscilloscope.

4. Describe the magnetic field or magnetic changes as shown in the

oscilloscope when an a square wave is feed to unshielded inductor and using
another inductor as a magnetic probe.

5. Does an inductor affects D.C.? Why?

Reference

https://www.youtube.com/watch?v=NgwXkUt3XxQ-Afrotechmods

https://www.youtube.com/watch?v=KSylo01n5FY&t=340s - The Engineering

Mindset

Electronic Circuits Fundamentals and applications

Fifth edition Mike Tooley
Fifth edition published 2020
by Routledge

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2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN
and by Routledge
52 Vanderbilt Avenue, New York, NY 10017

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