Electromagnetic Field (EMF)

ELECTROMAGNETIC FIELD
(EMF)
PRESENTED BY:
Group No.: 04
Group Member:
Amarta Sarkar (001)
Asadul Islam
Nasim Ali
(005)
(006)
Shawan Roy
(023)
Sabrina Wazir (039)

Department of Textile, BUBT
5 th Intake , Section : 1
ELECTROMAGNETIC FIELD
An electromagnetic field (also EMF or EM field) is a physical field

produced by moving electrically charged objects.
It affects the behavior of charged objects in the vicinity of the

field.
The electromagnetic field extends indefinitely throughout space

and describes the electromagnetic interaction.
It is one of the four fundamental forces of nature (the others are

gravitation, the weak interaction, and the strong interaction).
The field can be viewed as the combination of an electric field

and a magnetic field.
The electric field is produced by stationary charges, and the

magnetic field by moving charges (currents); these two are often
described as the sources of the field.
ELECTROMAGNETISM
Electromagnetismis one of the fundamental phenomenon in nature.

It is responsible for almost all the phenomena in our daily life.
Electromagnetismspans both electric fields and magnetic fields.
When observed individually, electricity and magnetism behave

differently but when unified, we can observe that both are
interdependent on each other and they cannot be separated from
each other.
In order to fully understandElectromagnetism, we have to look at

the four laws that governelectricityandmagnetism.
These areGausss laws in Electrostatics, Gausss law in Magnetism,

Amperes lawand Faradays law.
These laws were combined by James Clerk Maxwell in the year 1864
to give a complete set of relation and connection between both the
forces ofelectricityandmagnetism.
ELECTIC FILEDS AND MAGNETIC FIELDS

ELECTRIC FIELDS
MAGNETIC FIELDS
1. Electric fields arise from

voltage.
1. Magnetic fields arise from

current flows.
2. Their strength is measured

in Volts per meter (V/m)
2. Their strength is measured in

amperes per meter (A/m).
Commonly, EMF investigators
use a related measure, flux
density (in micro tesla (T) or
mille tesla (mT) instead.
3. An electric field can be

present even when a
device is switched off.
4. Field strength decreases
with distance from the
source.
5. Most building materials
shield electric fields to
some extent.
3. Magnetic fields exist as soon as

a device is switched on and
current flows.
4. Field strength decreases with
distance from the source.
5. Magnetic fields are not
attenuated by most materials.
USES FOR
ELECTROMAGNETS
An electromagnet does all the things that ordinary
magnets can do, but you can switch them on and off.
An electric bell uses an electromagnet to rapidly
pull the hammer over to the gong then release it.
For sorting scrap an electromagnet can be used to
pick up and put down magnetic materials, sorting
them from non-magnetic scrap.
In speakers an electromagnet is used to move a
cone very rapidly, causing sound waves.
In switches a small current can be used to operate
an electromagnet, which in turn can control another
circuit in which a much larger current might be
flowing. This isolates the large current from the
person operating the switch, making it safer.
USES FOR ELECTROMAGNETS
Diagram
of an
electric
bell
An
electromag
net being
used to pick
up scrap
Relays are
used in
circuit
control.
THE MOTOR EFFECT

A conductor carrying an electric
current may experience a force when
placed into a magnetic field.
To increase this force:
Increase
Increase
Increase
Increase
the field
the
the
the
the
current
number of coils
strength of the magnet
length of conductor in
To reverse this force:

Reverse the direction of the current
Reverse the direction of the
(permanent) magnetic field
NOTE: There is NO FORCE if the

conductor is parallel to the field.
Reverse the
field
Keep the current
the same
Keep the field

the same
Reverse the
current
Motion
reverses
Motion
reverses
Motion
Current
Field
DIAGRAM OF
AN ECLECTIC
MOTOR
ELECTROMAGNETIC INDUCTION
A potential difference is induced across the ends of a
conductor when it cuts across magnetic field lines. This is
called Electromagnetic Induction.
The same effect occurs if the conductor is held still and the
magnetic field changes.
The faster the conductor cuts the field lines (or the faster
the magnetic field changes) the bigger the potential
difference induced.
A SIMPLE DYNAMO
If the conductor forms
part of a circuit, a
current will flow.
In a dynamo, a coil is
rotated inside a magnetic
field, causing an
alternating current to
flow.
You can use the right
hand rule to prove to
yourself that a current
will flow all the way
around the coil of wire
when the coil is rotated.
TRANSFORMERS
TRANSFORMERS
A coil of wire is wound on

to one side of a soft iron
core. This coil is called the
primary coil.
When an alternating
current flows through this
wire, an alternating
electromagnetic field is
set up in the core.
TRANSFORMERS
If a secondary coil is then

wound on to the other side of
the core, this changing
magnetic field will induce an
alternating potential
difference across the ends of
the secondary coil.
TRANSFORMERS
Transformers step voltage up or down.
The size of the induced voltage is
given
byprimary
the ratio:
p.d. across
number of turns on primary
p.d. across secondary
number of turns on secondary

or
Vp
Np
Vs
Ns
TRANSFORMERS AND MAINS SUPPLY
Electricity is generated at the power station at

about 33,000V.
A step-up transformer steps this up to about
400,000V for transmission in overhead cables.
This is then stepped down for use in homes, to
230V (or for industrial uses, to 11,000V).
WHY?
TRANSFORMERS AND MAINS

SUPPLY
When the potential difference is stepped up, the

current is stepped down.
So there is a lower current flowing through the

wires.
This means that less energy is lost to heat (P=I2R).
So more of the power supplys energy gets to the

appliance, rather than being lost in the wires.
WHAT HAPPENS WHEN YOU ARE EXPOSED TO ELECTROMAGNETIC

FIELDS?
Exposure to electromagnetic fields is not a new phenomenon.

However, during the 20th century, environmental exposure to
man-made electromagnetic fields has been steadily increasing
as growing electricity demand, ever-advancing technologies
and changes in social behavior have created more and more
artificial sources.
Everyone is exposed to a complex mix of weak electric and
magnetic fields, both at home and at work, from the generation
and transmission of electricity, domestic appliances and
industrial equipment, to telecommunications and broadcasting.
Tiny electrical currents exist in the human body due to the
chemical reactions that occur as part of the normal bodily
functions, even in the absence of external electric fields.
ELECTROMAGNETIC FIELDS AT HOME

Electricity is transmitted over long distances via high voltage
power lines.
Transformers reduce these high voltages for local distribution
to homes and businesses.
Electricity transmission and distribution facilities and
residential wiring and appliances account for the background
level of power frequency electric and magnetic fields in the
home.
In homes not located near power lines this background field
may be up to about 0.2 T.
Directly beneath power lines the fields are much stronger.
House walls substantially reduce the electric field levels from
those found at similar locations outside the house.
TYPICAL ELECTRIC FIELD STRENGTHS MEASURED NEAR

HOUSEHOLD APPLIANCES
SUMMARY OF THE ICNIRP EXPOSURE GUIDELINES
European
power
frequency
Frequency
Mobile
phone base
station
frequency
Microwave
oven
frequency
50 Hz -50 Hz
900 MHz -1.8

GHz
2.45 GHz
Electric field
(V/m)
-Magnetic
field (T)
Power density
Power density
(W/m2) -Power
(W/m2)
density
(W/m2)
ELECTROMAGNETIC AND GRAVITATIONAL FIELDS

o Sources of electromagnetic fields consist of two
types of charge > positive and negative.
o This contrasts with the sources of the
gravitational field, which are masses.
o Masses are sometimes described as
gravitational charges, the important feature of
them being that there is only one type (no
negative masses), or, in more colloquial terms,
'gravity is always attractive'.
ELECTROMAGNETIC AND GRAVITATIONAL FIELDS
REFERENCES
Wikipedia
WHO
Google Search
Some Books:
1. Electromagnetic Fields (2nd Edition), Roald K.
Wangsness,
Wiley, 1986. ISBN 0-471-81186-6 (intermediate
level textbook)
2. Schaum's outline of theory and problems of
electromagnetics(2nd Edition), Joseph A. Edminister, McGrawHill, 1995. ISBN 0070212341(Examples and Problem Practice)

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ELECTROMAGNETIC FIELD

Sabrina Wazir (039)

An electromagnetic field (also EMF or EM field) is a physical field

It affects the behavior of charged objects in the vicinity of the

The electromagnetic field extends indefinitely throughout space

It is one of the four fundamental forces of nature (the others are

The field can be viewed as the combination of an electric field

The electric field is produced by stationary charges, and the

Electromagnetismis one of the fundamental phenomenon in nature.

Electromagnetismspans both electric fields and magnetic fields.

When observed individually, electricity and magnetism behave

In order to fully understandElectromagnetism, we have to look at

These areGausss laws in Electrostatics, Gausss law in Magnetism,

ELECTIC FILEDS AND MAGNETIC FIELDS

1. Electric fields arise from

1. Magnetic fields arise from

2. Their strength is measured

2. Their strength is measured in

3. An electric field can be

3. Magnetic fields exist as soon as

USES FOR ELECTROMAGNETS

USES FOR ELECTROMAGNETS

USES FOR ELECTROMAGNETS

THE MOTOR EFFECT

To reverse this force:

NOTE: There is NO FORCE if the

Keep the field

A coil of wire is wound on

If a secondary coil is then

number of turns on secondary

TRANSFORMERS AND MAINS SUPPLY

Electricity is generated at the power station at

TRANSFORMERS AND MAINS

When the potential difference is stepped up, the

So there is a lower current flowing through the

This means that less energy is lost to heat (P=I2R).

So more of the power supplys energy gets to the

WHAT HAPPENS WHEN YOU ARE EXPOSED TO ELECTROMAGNETIC

Exposure to electromagnetic fields is not a new phenomenon.

ELECTROMAGNETIC FIELDS AT HOME

TYPICAL ELECTRIC FIELD STRENGTHS MEASURED NEAR

SUMMARY OF THE ICNIRP EXPOSURE GUIDELINES

900 MHz -1.8

ELECTROMAGNETIC AND GRAVITATIONAL FIELDS

ELECTROMAGNETIC AND GRAVITATIONAL FIELDS

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