Intermediate 1 Physics

1
Intermediate 1 Physics

• Telecommunication

Questions and Answers
2
Intermediate 1 Physics

• Telecommunication

Questions 1 to 10
Questions 11 to 20
Questions 21 to 30
3

• 1. The telephone, telegraph and radio are all
  forms of communication systems.
• Which of these systems does not need a wire link
  between the transmitter and the receiver?

The radio does not need a wire link between
the transmitter and receiver.
This is because the signal (the message) is
carried on invisible radio waves which need no
substance to carry them.
4

• 2. Louise is listening to her radio and enjoying
  the music played by Atlantic 252. The signal is
  transmitted from a radio mast at the other end of
  the country.
•   (a) Describe the signal which travels from the
  radio station to the radio receiver.
• (b) At what speed does the signal travel?
• (c) What is transferred from the radio mast to
  the aerial in her radio?

The transmitter sends out invisible waves of
energy which we call radio waves.
Three hundred million metres per second (300 000
000 m/s)
energy
5

• 3. Raymond has drawn a block diagram for a radio
  but can only remember the first unit.
•  
•  
• (a) Complete the correct block diagram for the
  radio system.
• (b) Describe the function of any three units
  within the radio receiver.

aerial




tuner
decoder
amplifier
speaker
Aerial - Detects all radio waves. Tuner -
Selects one radio station. Decoder - Separates
the sound signal from the radio wave Amplifier -
Makes the small electrical signal stronger. Power
Supply - Supplies extra energy to the
amplifier. Loudspeaker - Changes the electrical
signal into sound.
6

• 4. A radio display shows a combination of letters
  and numbers as shown.
• The numbers tell the listener that the
  transmitter sends out 102.5 million waves in a
  certain time.
• How long a time does it take to send out 102.5
  million waves?

The time taken is one second.
(This is because frequency means the number
of waves produced every second.)
7

• 5. Jason is checking the times of the football
  broadcasts in his newspaper.
•   The two radio stations broadcast the same
  programme at the same time.
• However, the signals are not identical.
• In what way are the signals different from each
  other?

They are carried on two different radio
frequencies.
8

• 6. June is listening to a rock concert programme
  on her radio while her sister Alison is watching
  the same programme on her television.
•   (a) What type of wave is detected by the radio
  and the television set?
•  
•   (b) What is the difference between the two
  waves?

Radio waves.
They are different frequencies.
9

• 7. Each television station has a name which we
  are all familiar with.
• BBC 1 BBC 2 STV Channel 4 Channel 5
•  
• As well as the name, how can a particular
  broadcast station be identified?

It can be identified by its frequency.
10

• 8. A television is an electronic system, which
  can be represented by a block diagram, as shown
  below.
• (a) The diagram is incomplete.
• Complete the block diagram showing all the parts
  of a TV in the correct order.

aerial
tuner
Vision decoder
sound decoder
Vision amplifier
sound amplifier
speaker
Picture tube
11

• 8. A television is an electronic system, which
  can be represented by a block diagram, as shown
  below.
• (b) Describe the function of any four parts of
  the TV system.

- The aerial detects many radio signals and
changes them into electrical signals.
- The tuner selects the signal you want. (i.e.
the channel of your choice)
- The decoders separate the sound and vision
signals from the carrier wave.
- The amplifiers make the electrical signals
stronger.
- The loudspeaker changes the audio signal into a
sound wave, - The picture tube changes the video
signal into pictures.
12

• 9. A television screen is coated with 3 special
  chemicals which give out different colours of
  light energy (red, green and blue).
•  
• A viewer switches on the set and sees a yellow
  screen.
• She knows that yellow light is not emitted by
  the chemicals on the screen of any TV set.
• Explain why the viewer can see a colour on the
  screen which is not one of the 3 colours emitted
  by the chemicals on the screen.

The red and green dots are lit up on the TV
screen. These two colours of light combine to
make yellow.
13

• 10. High frequency radio signals are sent from
  the USA to Britain.
• The signals are received by a ground station in
  Cornwall.
•  
•  
•  
• (a) Describe what happens to the signal after it
  leaves the American ground station.
•  
•  
• (b) Weather forecasters on television show us
  detailed pictures of rain clouds over Britain.
• How is this kind of information gathered?

It is transmitted up to a satellite in orbit.
There it is amplified and then retransmitted to
Cornwall.
A satellite in orbit around the earth takes
pictures and transmits them back to earth.
14

• 11. An army unit on military exercise at the
  Earth's equator have positioned a satellite dish
  as shown.
• During their stay they find there is no need to
  change the position of the dish, which is
  pointing vertically upward. Communications are
  good and are never interrupted.
• (a) Why is there no need to continually alter
  the position of the satellite dish?
• (b) What name is given to the type of satellite
  being used?
• (c) What is the purpose of the curved reflector
  behind the aerial?

The satellite stays at the same point above the
equator.
Geostationary
To reflect the signals to a focus at the aerial.
15

• 12. Mirrors are used in many shops and help
  security guards to observe customers.
• (a) Describe what happens to light which strikes
  the mirror.
• (b) Complete the following diagram, showing the
  incident light ray and any other ray produced.

It reflects off the mirror at the same angle. The
angle of reflection is equal to the angle of
incidence.
reflected light ray
normal
16

• 13. Some lamps use a bundle of optical fibres.
• (a) What are optical fibres?
• (b) Describe how optical fibres are used in
  modern communication systems.

Long, thin strands of flexible glass through
which light can travel.
A signal is changed into variations in brightness
of light. These variations are carried from one
end of the fibre to the other by total internal
reflection.
17

• 14. Copper wire is used to transmit electrical
  signals.
• However, copper is expensive, heavy and produces
  heat energy.
• Signals can now be sent through optical fibres
  and less energy is wasted.
• (a) Describe the type of signal which is
  transmitted through an optical fibre.
• (b) At what speed does this signal travel
  through the optical fibre?

The signal travels through the fibre as
variations in the brightness of the light.
200 000 000 metres per second.
(light travels a little slower in glass than it
does in air.)
18

• 14. continued,
• (c) Complete the diagram below to show how the
  signal reaches the end of the optical fibre.

The light repeatedly reflects off the inside
walls of the fibre by total internal reflection
until it leaves at the far end.
19

• 15. Dawn is sitting at home using her personal
  computer. She can use the computer to gain access
  to information on the Internet.
• Information is transmitted to Dawn's
• computer along an optical fibre.
• What other device in the home might be
• connected to this optical fibre?

The telephone or television.
20

• 16. A television aerial is used to receive
  signals from the various TV transmitters.
• Some other houses in the street receive their
  television signals via optical fibres.
• Give one advantage and one disadvantage of the
  use of optical fibres to transmit signals.

Advantage dont need aerials/dishes not
affected by bad weather
Disadvantage the street/garden has to be dug up
to install it
21

• 17. A telephone message is transmitted from
  Glasgow to Edinburgh.
• (a) What name is given to the part of the system
  which sends the signal ?
• (b) What name is given to the part of the system
  which picks up the signal?

The transmitter.
(which is the microphone in the mouthpiece)
The receiver.
(which is the loudspeaker in the earpiece)
22

• 18. Telephones are of various types and are
  linked in different ways.
• The signal can be transmitted between phones
  using three
• different types of link.
• What are the three methods of transmitting a
  message between the transmitting and receiving
  telephones?

- by wires
- by radio signals
- by optical fibres
23

• 19. Mobile phones are being used more and more in
  the modern world.
• The mobile phone is a small portable telephone
  which has no external wiring, unlike conventional
  phones.
• (a) What are the two essential parts of a mobile
  phone, which allows the user to send and receive
  messages?
• (b) Using a mobile phone is not always the best
  way of contacting
• someone.
• Give one advantage and one disadvantage of
  mobile phone use.

the mouthpiece (transmitter)
the earpiece (receiver)
advantage people can get in touch quickly and
easily
disadvantage there is no signal in some areas of
the country its use can distract
drivers and cause accidents
24

• 20. While dismantling a telephone in the Physics
  lab,
• Alex discovers a microphone inside the handset.
• (a) Was the microphone found inside the
• mouthpiece or earpiece?
• (b) A loudspeaker was also removed from the
  telephone
• handset.
• Which part of the handset contained the
  loudspeaker?

inside the mouthpiece
the earpiece
25

• 21. Microphones are used in phones, tape
  recorders and public
• address systems.
• State the energy change which takes place in a
  microphone.

sound energy to electrical energy
26

• 22. Loudspeakers are used in phones, stereo
  systems, radios and televisions.
• State the energy change which takes place in a
  loudspeaker.

electrical energy to sound energy
27

• 23. A telephone cable contains bundles of copper
  wire which
• carry the signal.
• What is the approximate speed of the signal
  which travels
• along the wire?

300 000 000 metres per second (the speed of light)
28

• 24. A book publisher has to send a price list to
  a school.
• The price list is required urgently.
• (a) How could the price list be sent to the
  school very quickly? You should describe the
  transmitter, receiver and how the two are linked
  together.
• (b) Why is this method used so often nowadays?

It could be sent by fax.
The list is scanned by the sending fax machine.
The image is sent as signal along the phone line.
Another fax machine prints out a copy at the
other end.
It is much faster than sending a copy of the list
by post.
29

• 25. A signal generator is used to produce sounds
  from a loudspeaker.
• The loudness and the frequency of the note can
  be changed.
• The signal is displayed on the screen of an
  oscilloscope.
• (a) Describe how the oscilloscope pattern
  changes when the loudness of the sound increases
  and the frequency stays the same.

The height of the wave on the screen gets
bigger, but the number of waves does not change.
30

• 25. A signal generator is used to produce sounds
  from a loudspeaker.
• The loudness and the frequency of the note can
  be changed.
• The signal is displayed on the screen of an
  oscilloscope.
• (b) Describe how the oscilloscope pattern
  changes when the frequency increases and the
  loudness stays the same.

The number of waves across the screen
changes, but the height of the waves does not
change.
31

• 26. Use the information in the given passage to
  answer the questions below.
• (a) Complete the following sentences
• Satellites receive ..........................
  signals transmitted from Earth.
• The satellite then ..........................
  these .......................... signals back
  to ..........................
• (b) Explain the meaning of the term
  "Geostationary satellite"
• (c) Why are Geostationary satellites very useful
  in modern communication systems?

radio
radio
transmits
earth
A satellite which stays above the same point on
the equator.
There is no need to adjust the positions of the
ground station satellite dishes.
32

• 27. The graph below shows how the time it takes a
  satellite to go round the Earth changes with its
  height above the Equator.
• (a) Use the graph to find the height of a
  Geostationary satellite.
• (b) A spy satellite has to orbit the Earth twice
  each day.
• Use the graph to find the height of this spy
  satellite.

The period is 24 hours which is about 38 000 km
A period of 12 hours is at a height of 21 000 km
33

• 28. The telecommunication system linking two
  towns uses copper wires. This system is being
  replaced by one which uses optical fibres. Jamil
  and Gina want to compare the time taken for
  signals to travel through these two different
  types of connector, copper wires and optical
  fibres.
• A length of copper wire and a length of optical
  fibre are each connected to a telephone and a
  timing device as shown in the diagram.
• The timing device can measure the time it takes
  a signal to travel along the copper wire and the
  optical fibre.
• (a) Give two reasons why this not a fair test.

The wires and fibres are different lengths this
would make a difference
They are different thicknesses this would not
make a difference
34

• 28. (b) Jamil and Gina changed their test to make
  it fair.
• The time taken for the signal to travel each of
  the connectors is given in the table below.
• (i) Which signals, electrical or light, take the
  shortest time to travel along the connector?
• (ii) Explain in which connector, copper wire or
  optical fibre, the signals take least time to
  travel.

The electrical signals take the shorter time to
travel.
The signals take less time in the copper wire.
This is because the electrical signal travels
faster in the wires than the optical signal in
the fibre.
35

• 29. A student finds the following table in a
  physics book.
• It contains information on groups of radio
  waves.
• Complete the following diagram which shows the
  radio frequency
• ranges and their uses.
• Use the information in the table above to
  complete your diagram.
• The use of 300 kHz to 3 MHz has been filled in
  for you.

long range radio communication
high quality radio communication
TV and mobile phones
36

• 30. The following is part of a crossword puzzle
  that has clues about telecommunications.
• Complete the part of the crossword shown.
• The clues are as follows
• DOWN
• 1. This part of the radio needs a battery
• to supply it with energy.
• 2. Twenty four hour per day communication
• systems often use this type of satellite.
• ACROSS
• 3. Radio signals travel from Glasgow to
• London in a very short time. This is
• because radio waves have a very high
• 4. Mixing red, green and blue light
• produces this colour.

a m p l i f i e r
g e o s t a t i o n a r y
s e d
w h i t
37
Intermediate 1 Physics

• Telecommunication

End of Questions and Answers