8th Standard Syllabus

1. COMMUNICATION GADGETS
BY
U.N.BHASKARA
ASSISTANT TEACHER
GOVERNMENT JUNIOR COLLEGE
ALUR
HASSAND DISTRICT

2. What is
Communication?
It is process by which
information is exchanged
between individuals through
a common system of
symbols,signs or
behaviours.

3. World-Village?
Yes,our global world has become a village with
the help of fast growing technology.Now a days
communication has become much easier and it
reaches with the speed of
light.emails,Teleconferences,skype calls all
these communication gadgets had made our
world a global village.

4. Electro Magnetic Waves
These are the waves which has very long or short wave length
which are not visible ot our eyes.Mutually perpendicular electric and
Magnetic fields which are also perpendicular to the line of
propagation are known asa electromagnetic waves.They trave with
the speed of light.

5. Why should we Study EM
Waves?
It is because they act like vehicles in most of the
modren communication devices.Here you can see
the photograps of scientis who worked for em
waves
James Clerk Maxwell
1864
Heinrich Rudolf Hertz
1887

6. Theory Behind the study of Electromagnetic Waves
Electromagnetic wave theory was first proposed by James Clerk
Maxwell,in the year 1864.They were first experimentally produced
and demonstrated by Hertz in the year 1887.They are also called as
Hertizian Waves
The use of electromagnetic
waves in sending wireless
messages or radio
communications was first
demonstrated by the Indian
scientists Acharya Sir
J.C.Boase.

7. RADIO
Very Old Radio Guglielmo Marconi
1874-1937
Radio is still the most popular electronic device used to listen to
music,speeches and weather bulletins.The lowcost device namely radio
does not require much technical skills to operate.

8. Radio
Radio Communication Involves two things
1.Radio Transmitter.
2.Radio reciever.
1.Radio Transmitter.
Music,Speech or weather bulletins consists
of sound waves which are produced by
vibrations.This information is called
intelligence. These sound waves are
converted into electrical signals,called
Audio Frequency Waves. Micophones
convert the vibrations into AF.

9. Working Of Radio Transmitter
Microphone AF Signals
Amplified
AF
Signals
Modulations
AF+RF
RF Waves
Amplification
Antenna
When the sound is input to the microphone the membrane inside it virbates there by
converting the audio signals into electrical input called as AF waves. This AF is amplifed
in amplifier.The process of superimposing or mixing AF signals on RF waves is called
modulation.The modulated waves are further amplified and transmitterd by transmitting
towers or antennas.

10. Radio Receiver
Modulated
Waves Demodulator Amplifier
Antenna
Speaker
Antenna receives the modulated waves.Demodulator
seperates RF from Af signals the process is called
demodulation.The signals are amplifed and fed to the
speaker to rpoduce the original sound.

11. Television
It is an electronic device which not only gives audio but also video signals thereby
entertaining crores of poeple arround the world. The credirt of this must go the the
Physist JHON LOGIE BAIRD.

12. Working of Television Transmitter
Photo
cells V.F.Signals Amplification
Light
T.V.Camera
Modulation
VF+RF Amplifier
Antenna
RF
The image of an object is made fall on a plate using T.V.camera.This plate is called
signal plate.The plate consits of many phot cells.The light from the object is
converted in to video signals or video frequency waves or VF in short. Before this
process the image is scanned as dots and lines by the scanner.The VF signals are
amplified and modulated as RF waves and then amplified and transmitted through
antennas.Sound is transmitted as in a radio.

13. T.V.Receiver
Modulated
Waves Demodulator Amplifier
Antenna
Speaker
Antenna receives the modulated waves. Channel
selection is nothing but selection of frequency of a
T.V.station.after demodulation the VF signals are fed
to the picture tube called cathode ray tube. The
cathode ray tube prdouces original picture. The
sound is reproduced as in the radio receiver.

14. FAX
Alexander Bain is the inenvter of
FAX.He is a technician and clock
maker.
The long form of FAX is facsimile
transmission.
(Telecommunications) an
international system of
transmitting a written, printed, or
pictorial document over the
telephone system by scanning it
photoelectrically and reproducing
the image after transmission.
Often shortened to: fax

15. Working of FAX
A fax machine scans the document by light and image
and the image is changed into electrical signals by
photo cells. The message travels through the
telephone lines and received by the fax machine at
the other end. After decoding, machine produces the
copy of the original document. Every FAX machine
has a number like a telephone. This has tobe dialled
before sending the message.

16. Working of Telephone
Telephone was
invented by
Alexander Graham
Bell.He was a British
inventor,Scientist,En
gineer and Proffessor
The sound waes are
converted into electrical
signals by the mouth
piece. The signals reach
the ear piece at the other
end by cables.

17. Working of Mobile
It is a two way radio
system.It consists of
both radio transmitter
and receiver.It also
consists of a portable
microchip called Sim
card.(SUBSCRIBER
INDXE MODULE).
Sound waves are
converted into radio
frequency waves and
travel without the help
of the cable and reach
the reciever at nearby
base station. The base
station sends the radio
waves which are
detected by the receiver.

18. Advantages of mobile

Communication between two persons even if
they are moving.

Communication to and from land line phone.

Voice message, text message facicilities

It can be used as a mini computer.

Linking of entire globe by tlelcommunication
usinf geostationary satellites.

19. Internet
A means of connecting a computer
to any other computer anywhere in
the world via dedicated routers
and servers. When two computers
are connected over the Internet,
they can send and receive all
kinds of information such as text,
graphics, voice, video, and
computer programs.

20. Founder of Internet
Vint Cerf