Intermediate 1 Physics Revision Booklet.
Telecommunications
Telecommunications is the name given to the process of sending
information over a large distance.
All telecommunications systems send information from a transmitter to a
receiver.
A common method of sending information
is by using a radio. Radios are useful
because they do not need wires to connect
the transmitter and receiver. A radio signal is
sent from the transmitter to the receiver as a
wave. The radio wave carries energy. Radio
waves travel very quickly through the air, in
fact they travel at 300 000 000 metres per
second. This means that they could go more
than six times around the Earth in one
second.
For most of us a radio is used to listen to music,
but there are many other applications. The
emergency services use radios to keep in touch
with their bases. Taxi drivers use radios to get
information about pick-ups.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
All radio receivers are made up from the same basic parts. A diagram
showing these parts in order is shown below.
Aerial
Tuner
Decoder
Amplifier
Loudspeaker
What do the parts do?
Aerial-this part picks up all the radio signals that are present. This will
normally be hundreds of radio signals from many different sources.
Tuner-this part selects one signal from the hundreds that are there. It has
nothing to do with fish.
Decoder-this part takes away the high frequency part of the radio
signal,[the carrier wave],leaving the audio[sound] part.
Amplifier- this part increases the energy of the audio signal that comes
from the decoder.
Loudspeaker-this part changes electrical energy into sound energy.
Radio stations have to distinguish
themselves from each other so that
their listeners can choose the
correct station to listen to.
Radio stations have different frequencies for their radio signals. The
frequency of a radio signal is the number of radio waves produced each
second. There is a word we can use instead of saying ‘the number of radio
waves produced each second’, it is hertz. Hertz is called the unit of
frequency. It can be written as an abbreviation, Hz. Radio stations have
high frequencies, Real Radio is 101 000 000 Hz.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Television
Television is very similar to radio in many ways. The main difference is
that televisions produce a picture as well as sound. Because of this the
diagram of the parts of the television is different.
Aerial
Tuner
Vision
decoder
Audio
decoder
Vision
amplifier
Audio
amplifier
Tube
Speaker
The Aerial, Tuner, Decoder, Amplifier and Loudspeaker do exactly the
same job in the television as they do in the radio.
The Tube changes electrical energy into light energy.
The tube has three types of special paint that gives off light of a particular
colour. The three colours of light produced are RED, BLUE and GREEN.
Mixing these three colours produces all other colours that you see on a TV
screen.
RED + BLUE
RED + GREEN
BLUE + GREEN
RED + BLUE + GREEN
= MAGENTA
= YELLOW
= CYAN
= WHITE
Varying the strength of the three original colours can produce other
colours.
Example extra RED + normal GREEN
= ORANGE.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Satellites
Satellites have changed communication around the
world dramatically. Now it is possible to use satellites
to send signals from one part of the Earth to another
thousands of miles away.
The satellites used in this type
of communication are called
GEOSTATIONARY satellites.
They are special because they
stay above the same point on
the Earth’s surface at all times.
The satellite transmitter and receiver have a particular shape. You may
have noticed this common shape from the satellite dishes on the sides of
people’s houses. The dishes have a curved shape to increase the strength
of the signal falling on the aerial.
The diagram below shows what happens to the signal from the satellite
when it reaches the dish. The dish picks up the signal over its curved
surface and reflects all of the signal to the aerial that is placed at the focus
point.
Curved
Dish
Aerial
Incoming
Signal
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Optical Fibres
When light strikes an object it will be reflected. We are able to see objects
because they either produce light, like a lamp or the sun, or they reflect
light into our eyes, which is practically everything we see.
Usually we will use mirrors when we want to cause light to reflect. If the
mirror is plane[flat] then the light reflects in a specific way.
angle of
incidence
i r
angle of
reflection
normal
The angle that the light strikes the barrier is the same as the angle that the
light reflects from the barrier.
This fact is used in a type of signal transfer, the transfer of information
using optical fibres. An optical fibre is a thin glass thread that will carry
light signals. A signal is converted into light and passed along the fibre.
Each time the signal meets the surface of the fibre it is reflected back
inside and will go from one end to the other of the fibre.
The signal passes along the fibre at a speed of almost 200 000 000 m/s.
This is slower than the speed that radio waves travel through air.
Although the light signal does not travel as quickly it can carry much more
information and is less likely to have interference.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Optical fibres are used in many modern applications in the home.
Telephone services: 1471 and 1571
Cable
television
Home banking
Internet
Optical fibres have meant that these services can now be accessed in many
homes, that is a great advantage of this type of system. There are
disadvantages though; not all homes are connected to the optical fibre
system. The roads and pavements have to be dug up to lay the cables
containing the fibres.
Telephone
The telephone has been used as a method of
communication since 14 February 1876 when
Alexander Graham Bell registered his
invention.
The modern telephone is very similar to his
original invention.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Telephones are like all other forms of communication, a signal is sent
from a transmitter to a receiver.
The signal can be sent by using metal wires, optical fibres or radio waves
between the transmitter and the receiver.
Wire carries signals
to and from the
telephone
Earpiece
Loudspeaker
Electrical to sound
Mouthpiece
Microphone
Sound to electrical
The names of the parts of the telephone handset, the devices contained in
them and the energy change that takes place in them are shown on the
diagram above.
If the signal is sent along a wire it travels at almost 300 000 000 m/s.
A mobile phone uses radio waves to transfer
the signal.
The mobile phone acts as both transmitter
and receiver for radio waves.
Radio waves also travel very quickly at a
speed of 300 000 000 m/s.
Many people have mobile phones these days. They have the advantage of
not needing wires so they can be used almost anywhere. A disadvantage is
that mobile telephone calls are more expensive than ordinary home
phones.
A useful application of the telephone lines is to send facsimile messages,
more commonly known as FAX. This allows pictures and diagrams to be
sent.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
In all telephone systems we need to change an electrical signal into sound
so that we can hear the message sent to us. The electrical signal can be
examined using a device called an oscilloscope. The pattern on the
oscilloscope screen can give an indication of what the signal would sound
like when it is changed to sound by the loudspeaker.
telephone
handset
oscilloscope
wire carrying
signal from
telephone
If we know what a particular signal looks like on the screen, we can
compare the sound produced with any other signal pattern given.
This is the original pattern.
If the sound gets louder the height of the
pattern gets bigger [diagram A]
If the sound gets higher pitch the number of
waves on the screen increases [diagram B]
diagram A
diagram B
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Telecommunications Learning Outcomes
• Radio
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Radio communication does not require wires between transmitter and
receiver.
Radio signals are waves that transfer energy.
Radio signals travel at 300 000 000 m/s
How to complete a block diagram of a radio receiver.
Describe what the following parts of a radio receiver do: The aerial ,
tuner , decoder , amplifier and loudspeaker.
The number of of waves produced in one second is the frequency of a
signal.
The frequency of a signal is measured in Hertz.
Radio stations can be identified by the frequency of their signal.
• Television
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Television signals have a higher frequency than radio signals
Just like a radio station TV stations are identified by the signal
frequency.
How to complete a TV block diagram
Describe what the following parts of a TV receiver do: The aerial ,
tuner , amplifiers, tube and loudspeaker.
All colours on a TV screen are produced from RED, BLUE and
GREEN light.
• Satellites
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How satellites are used.
A geostationary satellite remains above the same point on the Earth’s
surface.
Curved reflectors on an aerial make the signals stronger
Explain why curved reflectors on an aerial make the signals stronger.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
• Optical Fibres
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Light can be reflected
The angle of incidence is equal to the angle of reflection
An optical fibre is a thin glass thread which can carry signals.
Optical fibres are used in telecommunication.
Information passes along optical fibres as light signals
The signals travel along the optical fibre at a speed of 200 000 000
m/s [slower than in air]
The light signal reflects from the inside surface of the fibre to pass
along it.
Optical fibres have allowed more information to be sent into homes
i.e.cable TV,digital phones,internet access etc.
Advantages and disadvantages of optical fibre technology.
• Telephone
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Signals are sent out by a transmitter and picked up by a receiver
Telephone systems may use metal wires, optical fibres or radio waves
to carry the signal
A mobile phone acts as both transmitter and receiver
Advantages and disadvantages of mobile phones
The mouthpiece of a phone contains a microphone
The mouthpiece of a phone is the transmitter
The earpiece of a phone contains a loudspeaker
The earpiece of a phone is the receiver
The microphone changes sound to electrical energy
The loudspeaker changes electrical to sound energy
The signal in a metal telephone wire travels at a speed of 300 000 000
m/s.
Fax is the process of sending documents and pictures using the
telephone system
Advantage of using fax.
Draw and recognise the effect of the signal pattern on an oscilloscope
due to a change in;
» Loudness of sound
» Frequency of sound
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Revision Questions
Radio
1. Why is radio a useful method of communication?
2. At what speed do radio waves travel through air?
3. Copy and complete the following sentence
Radio signals are sent from the _______________ and are
picked up by the _______________.
4. What is carried by radio waves?
5. Copy and complete the block diagram of the radio receiver below.
Aerial
Decoder
6. Give a brief description of the function of the five parts of the radio
receiver.
7. What is different about the radio signals from Beat 106 and Real Radio.
8. What is meant by the frequency of a radio signal?
9. What is the unit of frequency?
Television
10. The table below contains information on two sets of signals that are
broadcast in Scotland.
Set
Frequency (hertz)
A
1 215 000
B
628 000 000
One set of signals is for a radio station and the other is for a TV
station.
a) Which set of signals could be the TV signals?
b) Explain your answer to part a).
11. Draw a block diagram for a television in the same style as Q5.
12. Describe the function of any part of the above diagram that does not
appear on the radio block diagram.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
13. What are the three colours of light produced by the paint on a TV
screen?
14. Copy and complete the table below showing the colour produced on a
TV screen when different paints are lit.
Colour lit
Colour seen
on screen
Red
Blue
Red + Blue
Blue +
Red +
Cyan
Yellow
+
15. Explain how colours other than those in the table above can be
produced.
Satellites
16. Give a brief description how satellites are used to send signals from
Australia to Scotland.
17. Communications satellites are geostationary satellites.
What is meant by geostationary?
18. Copy and complete the diagram below showing a satellite TV
receiving dish.
Curved
Dish
Incoming
Signal
19. Explain why the set up above can make the signal stronger.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Optical fibres
20. Copy and complete the diagram showing two rays of light striking a
mirror below.
B
normal
A
21. What is an optical fibre?
22. Copy and complete the diagram showing a ray of light passing through
an optical fibre.
23. Which telecommunications systems use optical fibres. You should be
able to give at least three examples.
24. Copy and complete the table below
Type of signal
Radio signal through air
Light signal through optical fibre
Phone signal through metal wire
Approximate speed of signal(m/s)
300 000 000
25. Write a short note on the advantages and disadvantages on the use of
optical fibres to send signals into the home.
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
Telephone
26. Copy and complete the following passage.
A telephone like all telecommunication systems sends signals from a
__________ to a ____________. These signals may be sent along metal
________, __________ fibres or through the air as _________ waves.
27. Give advantages and disadvantages of a mobile phone. Present your
answer in a table with appropriate headings.
28. Look at the diagram of a telephone handset below.
Name the parts labelled X and Y.
For each part give the name of the electrical component used and give
the energy change that takes place.
X
Y
29. What device could be used to send a document by telephone
transmission.
30. What is the advantage of using this system?
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft
31. The trace on an oscilloscope showing the signal pattern for a signal
that is sent to a loudspeaker is shown below.
Give the change that you would hear in the sound from the loudspeaker
for each of the other four patterns shown below A, B, C and D.
A
B
C
D
Dick Orr 2002 Intermediate 1 Physics Revision Book Draft