Telecommunications Unit - Lessons

8/3/2019 Telecommunications Unit - Lessons

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Unit 2: Telecomms Communicating Lesson 1

The need to communicateEver since humans have been able to talk, they have tried to communicate over

long distances.

Telecommunicationmeans communicating over long distances.Think of ten ways of communicating over a distance.

The diagrams below may help you to think.

Use your ideas to complete the first column of the table on the next page. A

couple have been done for you.

Knox Academy Physics Dept 1


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way of communicating advantages disadvantages

shouting

semaphore (flags)

Any method of communication has advantages and disadvantages, such as:

ADVANTAGES DISADVANTAGES

Very fast Takes time

Private Not private

Long distance Short distance

Wireless link/mobile Needs to be linked by wire or cableCheap Expensive

Easy to do Difficult to do

Now complete the table, choosing at least one advantage and one disadvantage

for each way of communicating.



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Faster and fasterThousands of years ago, during the Greek wars, one army won a

mighty victory. The commander had to let the king know as soon as

possible. A soldier was given the message, and told to run to theking as fast as he could. The soldier ran 26 miles in just over two

hours. He gave the message to the king, then dropped down dead.

This happened in a place called Marathon and thats why the

longest Olympic race is 26 miles long.

Over the years, the speed of messages has increased.

Use the formula: speed = distance

Time

to work out the speeds of these methods of communicating.


In 490 BC

A Greek soldier runs 26 miles in 2

hours.

In 1661

A letter sent from London to

Edinburgh by horse 600 kilometres

in 40 hours.

In 1838

A Morse Code message sent along awire 500 kilometres in 0.002

seconds.

1962

A phone call from Edinburgh to NewYork by satellite 120,000 kilometres

in 0.4 seconds


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Unit 2: Telecomms Breaking the code Lesson 1: extra

Keeping secretsMost early methods of telecommunication were not private.

Messages It was easy to intercept messages. This could be dangerous,

especially in wartime. A Roman general once had a soldiers head shaved. Themessage was tattooed onto the soldiers scalp. Once his hair had grown, he was

sent to deliver his message.

Codes Codes are safer but they can be broken. Try to break these codes.

If you get stuck, ask for a hint.

1. DBO ZPV SFBE UIJT?

2. 19.15.13.05. 03.15.04.05.19. 01.18.05. 20.15.15. 05.01.19.25.

3. CXAZN YXOZU WZOZRXXK OXUXTXX ZTZHXXIXXS?

4. Why, in this life, no one persons head is made from difficult blancmange.

The pig-pen codeYears ago, most schoolchildren knew the pig-pen code. Nowadays, its very

rare. It works like this.

A B C

D E F

G H I

J K L

M N O

P Q R

Knox Academy Physics Dept

S

T U

V

W

X Y

Z

Instead of A, write

Instead of K, write

Instead of T, write

Instead of X, write

4


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Unit 2: Telecomms Breaking the code Lesson 1: extra

Turn this message into pig-pen code.

Send more troops to the front line.

Now write your own short message in pig-pen code. Dont make it any more

than six words. See if your partner can decipher it.

And finallyCan you work out this one? Its all based on the grid.

0 1 2 3 4

5 A B C D E

6 F G H I J

7 K L M N O

8 P Q R S T

9 U V W X Y

52.74.53.54.51.82.54.50.70.54.82.83.92.63.73.92.50.82.83.



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Unit 2: Telecomms Sending radio signals Lesson 2

Messages through the air

Morse code Morse code was an early method for sending signals. It used

electric currents sent along wires. But this caused problems. To send a message500 kilometres, you needed a wire 500 kilometres long. Even if you had the wire

in place, it could be easily damaged.

Radio signals In 1901, an Italian scientist called Marconi sent radio signals

through the air from America to Britain. This was a very important because it

led to the development of radios to receive the radio signals.

Within a few years, most homes had a radio. But because no wires were used,the first radios were called wirelesses.

A transmitter is used to send radio signals.

A receiver is used to pick up radio signals.

Radio communication does not need wires between thetransmitter and the receiver.



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Sending and receivingYour teacher has set up a model radio transmitter in the lab. This can be used to

send radio messages a short distance. You can pick up the messages on an

ordinary radio.

Watch the demonstration. Label the diagram, and answer the questions.

1. What did you hear on the radio?

2. Why did your teacher not attach an aerial to the transmitter?

3. How do you think the information travelled from the transmitter to the

radio?

4. Were the transmitter and the receiver (the radio) connected by wires?



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Radio signalsRadios used to be called wirelesses because there were no wires between the

transmitter and the receiver. But if there are no wires, how do signals get from

one place to another?

Key facts

Radio signals are waves. Like all waves, radio waves transfer energy. Radio signals travel at 300 million (300,000,000) metres per

second.

Questions

1. The Moon is about 450,000,000 metres away from the Earth. How long

would it take a radio signal to travel from the Earth to the Moon?

2. The equator of the Earth measures about 40,000,000 metres. About how

many times could a radio signal go round the Earth in 1 second?

http://www.dorlingkindersley-uk.co.uk/static/cs/uk/11/clipart/space/image_space007.html


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Unit 2: Telecomms Radio history Lesson 2: extra

What are Waves?

We have already talked about waves but what are they and what do they?

Perhaps the easiest place to start is at the beach. We have all seen waves

crashing onto the beach and if you have been in the water at the time you will

have felt the energy that they carry.

Radio waves carry

energy too. Theycarry the signals from

the radio transmitter

to your radio.

Although we cannot

see radio waves we can think about them looking like water waves.

Listen to your teacher describing radio waves and then complete the diagram

and sentences below.

The wavelength of a wave is_________________________________________

________________________________________________________________

The frequency of a wave is__________________________________________

________________________________________________________________

Radio over the years

Read this history of radio development, then answer the questions.


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Who discovered radio waves?

In the 1860s, James Clerk Maxwell used maths to show that radio waves must

exist. James Clerk Maxwell was a famous Edinburgh physicist. He has a

building at Edinburgh University named after him. However, no-one had ever

seen radio signals, or noticed any effects. The race was on to try to find evidenceof radio waves but it took some time.

Can you show that there are radio waves?

In 1887, the German Heinrich Hertz finally showed that radio waves existed. He

used a simple spark transmitter. This gave off a burst of radio waves that

travelled across his laboratory. A receiver picked up the radio waves, and used

the energy in them to create a very tiny spark.

How far can radio waves

travel?

In 1894, the Italian scientistGuglielmo Marconi started

doing experiments with

radio waves. At first, he could only send signals a few metres. After further

work, he increased the range to 2 kilometres. Marconi described his ideas to the

Italian government, but they werent impressed. Because of this, Marconi

moved to England.

Marconi carried on increasing the range of radio signals. By 1899, he was

sending signals across the English Channel. People were starting to take noticeof this new method of communication. Finally, the big breakthrough came in

1901. Marconi sent a radio signal across the Atlantic, from Ireland to the USA

a distance of about 4,000 kilometres.

How was radio technology improved?

Ireland

USA

Atlantic

Ocean


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Radio technology steadily improved over the next few years. Marconi was ready

to broadcast to the public by 1920. Only two daily programmes were broadcast,

but they had a big effect. The famous international singer Dame Nellie Melba

took part in one on 20th June 1920. The popularity of radio grew, and the BBC

was set up in 1922. At first it could only broadcast signals to people living

within 60 kilometres of London. By 1932, the BBC was broadcasting all overthe world.

FM

FM stands for Frequency Modulation. This is a way of changing the radio

wave so that it can carry a better signal.

Most radios station now broadcast on FM, as it gives better quality sound. FMwas developed by Edwin Armstrong in 1934. It took many years for him to

convince other people that FM was the future of radio. FM broadcasting did not

start until in 1954 in the UK.

Satellites

Today, most international radio transmissions are handled by satellites. The first

communications satellite was called Telstar. It was launched in 1962, and was

also used to send the first TV pictures between the USA and Britain.

Ring 60 km from London The whole world


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1. What nationality was James Clerk Maxwell?

2. How many years did it take for scientists to show that radio waves

existed?

3. Describe Hertzs experiment.

4. Why did Marconi move to England?

5. Messages had been sent across the Channel using a cable on the sea bed.

What are the disadvantages of this method?

6. How many years ago did a radio signal first cross the Atlantic?

7. Why do you think the radio programmes broadcast in 1922 had a bigeffect?

8. Why do most radio stations now broadcast using FM?


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Unit 2: Telecomms Parts of the radio - 1 Lesson 3

Putting it togetherAll radios, whether very simple or very complicated, have the same basic parts,

put together in much the same way.

What to do - 1

1. Collect a set of Radio Cards.

2. Put them together in the right order.

3. Check with your teacher.

4. Copy the diagrams on the cards into these spaces.

What to do - 2

We sometimes show the parts of the radio as a block diagram. This just has thenames of the parts. Complete this block diagram.

AERIAL


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The aerialTo work properly, all radios need an aerial. But sometimes, its not obvious.

What to do1. Collect a small pocket radio.

2. Set it to AM. Dont extend the metal aerial. Tune it into a strong station.

3. Move the radio around. What happens to the signal?

4. Switch to FM and try to pick up a signal.

5. Now extend the metal aerial? Is the reception different in any way?

The job of the aerial is to collect radio signals.When you are listening on AM, youre using an internal aerial. If you move theradio around, this can affect the reception.

When you are listening on FM, youre using an external aerial. Without this

aerial, its often very difficult to pick up a signal.

Radio signals and metal boxesTune the radio to a strong station, then put it into a box made from metal mesh.

1. What happens when the radio is in the box?

2. Can you explain why?

3. Can you explain why radio reception in this school is poor?


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Unit 2: Telecomms Marconi Lesson 3: extra

Guglielmo MarconiPractical radio was developed by the Italian scientist, Guglielmo Marconi.

Collect Information Card 2.3. Read it carefully, complete the Marconi Fact File,and then answer the questions.

1. What was unusual about Marconis childhood?

2. Where did Marconi carry out his first experiments?

3. Which other scientists work was important to Marconi?

4. Why did Marconi move to England?

Date of birth:

________________

Date of death:

_______________

Place of birth:

_______________

Education:

__________________

What he worked on

___________________

___________________

___________________

___________________

____________

Achievements

___________________

___________________

___________________

___________________

____________


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Unit 2: Telecomms Marconi Lesson 3: extra

5. Why do you think that the Post Office was interested in Marconis work

on radio?

6. What is a patent and why was it important for Marconi to get a patent for

his work?

________________________________________________________________

7. How did Marconi demonstrate the power of radio in 1901?

8. Describe how was radio used to bring Dr. Crippen to justice.

9. Why do you think that the Dr. Crippen case helped radio to become more

popular?

10. Why was radio important during World War 1?

11. Marconi wasnt part of the Italian army, but he still received a medal.

Why do you think this happened?

12. How old was Marconi when he died?


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The tunerThe air around you is full of radio signals

signals from all the different radio stations

the radio waves given off by electrical sparks

the radio waves given off by the Sun and so on.

For a radio to work, its important that only one signal is selected.

The tuner selects one radio signalStudy this table, listing the frequencies of different radio stations. Use it to

answer the questions.

AM (amplitude modulated) FM (frequency modulated)

Station Frequency Station Frequency

Clyde 2

Forth

Northsound

Radio Scotland

Radio 4

Radio 5

1152 kHz

1548 kHz

1035 kHz

810 kHz

198 kHz

909 kHz

Clyde 1

Forth

Tay

Northsound 1

Scot FM

Radio 1

102.5 MHz

97.3 MHz

102.8 MHz

96.9 MHz

100.3 MHz

99.8 MHz

kHz stands for kilohertz. One kilohertz = 1000 hertz.

MHz stands for megahertz. One megahertz = 1,000,000 hertz.

1. Do AM or FM stations have the higher frequency?

2. Which AM station has the lowest frequency?

3. Which FM station has the highest frequency?

4. Which stations frequency is between Northsound and Radio 1?


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The amplifierThe radio signals picked up by a radio are turned into tiny electrical signals

inside the radio. If you want to turn these tiny signals into sound and listen to

them, they need to be boosted.

An amplifier boosts the tiny electrical signals in a radio.How can we see this happen?

What to do

Your teacher will use set up two oscilloscopes. These will be used to examine

the electrical signal going into an amplifier and the electrical signal coming outof the amplifier.

Signal going into the amplifier Signal coming out of the amplifier

INPUT SIGNAL OUTPUT SIGNAL

Carefully draw the traces shown on the two oscilloscope screens.

1. How are the signals different?

2. How will this affect the volume of the sound from the radio?

3. The amplified signal has more energy. Where has this energy come from?


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Hearing the signalSo far, you have learnt that:

the aerial collects lots of radio signals

the tuner selects just one of those signals

the amplifier boosts the signal, using energy from the battery

None of this is much good unless the electrical signal is converted into sound so

you can hear it. This is done by the loudspeaker.

Copy and complete this key point:

The loudspeaker converts _________ energy into _______ energy.Making a loudspeakerIts quite easy to make your own basic loudspeaker. Follow these instructions.

1. Collect a metal C-core, and long length of wire, two magnets and a tin lid.

2. Wrap the wire around the metal C-core as many times as you can.

3. Connect the two ends of the wire to the amplifier that your teacher has set

up.

4. Stick the tin lid to the C-core with the two magnets and listen. You may

have to hold the magnets tight against the tin lid.

5. Draw a labelled diagram of your loudspeaker set-up.


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Improving a speakerDoes the size of a loudspeaker make any difference to the quality of the sound?

Try making your loudspeaker with different sizes of tin lids. Fill in your resultsin this table.

diameter of lid

cmquality of sound

Write down any conclusions that you have come to.

Real loudspeakersYour teacher will show you a working loudspeaker. The front of the speaker has

been removed so you can see the moving parts. Watch the demonstration, then

answer these questions.

1. Which part of the loudspeaker moved?

2. Describe the movement when the loudspeaker was playing a low note.

3. How did the movement change when the loudspeaker was playing a high

note?

4. How did the movement change when the loudspeaker was playing a loud

note?


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Unit 2: Telecomms Build a radio Lesson 5: extra

D-I-Y radioYouve learnt that a radio has just a few basic parts. This makes it quite easy to

build your own radio.

Collect:

a battery pack

an FM receiver board and an aerial

a power amplifier board

a loudspeaker

four leads

two yellow connectors and one brown connector.

Connect the equipment together like this.

1. Connect the aerial to the FM receiver board. Can you pick up any radio

stations? Which ones?

2. Which control do you adjust to alter the volume?

3. Try rotating the aerial. Does it make any difference to the signal you

receive?

Power amplifier

loudspeaker

battery

pack

FM receiver

brown

connectoryellow

connectoryellow

connector


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Unit 2: Telecomms Build a radio Lesson 5: extra

Frequency and wavelengthRadio stations transmit radio waves at certain frequencies. But we can also

measure the wavelength of the radio waves. This table shows the wavelengths of

radio waves of different frequencies. Use the information to plot a line graph ofwavelength against frequency.

wavelength (metres) frequency (hertz)

300 1,000,000

150 2,000,000

100 3,000,000

75 4,000,000

60 5,000,000

50 6,000,00043 7,000,000

38 8,000,000

Title: ______________________

QuestionTry multiplying together each pair of wavelength and frequency values. What do

you find? Does it mean anything?

0

50

100

150

200

250

300

0 50 100 150 200 250 300 350 400


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Unit 2: Telecomms Radio freqencies Lesson 6

Sorting out the stationsWith all those different radio stations broadcasting, how come the signals dont

get mixed up? Why can you tune in to Radio 1, but not hear all the other

stations?

Complete these key points.

Radio stations can be identified by the f_______ of the radiosignals they t________.

The frequency of a radio station is the number of radio w_____ itproduces in one s_______.

Frequency is measured in h______ (Hz). 1500 waves per second is1500 h_____.

Radio stations often use their frequency as part of their name. For example, the

radio station Beat 106 transmits on 106 megahertz.

What to do

Collect Info Card 2.6. Use it to answer these questions.

1. What frequency does Tay AM transmit on?

2. Which station transmits on 1152 kHz?

3. Which radio stations transmit to West Lothian?

4. All the FM stations have something in common about their frequencies.

What is it?

5. All the AM stations have something in common. What is it?


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Unit 2: Telecomms Radio freqencies Lesson 6

6. Is Radio Scotland a FM station or an AM station? Explain your answer.

7. Is NorthSound1 a FM station or an AM station? Explain your answer.

8. Forth 1 FM and The Wave 102 both broadcast on 102.0 MHz. How can

two stations both broadcast on the same frequency without interfering

with each other?

9. Which other two stations broadcast on the same frequency? Does your

answer for question 8 explain this one as well?

10. Someone living in Glasgow wants to hear sports news. Which two

stations could they listen to?

11. Which FM station has the highest frequency?

12. What does the MFR stand for in MFR AM, broadcasting on 1107 kHz?

13. A listener in Edinburgh wants to hear up-to-date music. Which stations

could they listen to?

14. Real Radio FM broadcasts on 100.3 MHz and 101.1 MHz. Why does it do

this?


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Unit 2: Telecomms Radio quizzes Lesson 6: extra

AnagramsSolve the anagrams all the answers are words connected with

telecommunications.

DARIO _________________ OMICRAN __________________

NUTER _________________ THREZ __________________

REALIA _________________ REMOS __________________

GILSAN _________________ LEXMAWL__________________

A to Z (well, some of them)A: used to boost a small electrical signal __________________

B: what an amplifier does to a signal __________________

C: used to send secret messages __________________

D: one of the basic parts of a radio __________________

E: loudspeakers convert __________ energy into sound __________________

F: measured in hertz or kilohertz or megahertz __________________

H: unit of frequency __________________

J: Maxwells first name __________________

L: radio signals travel at the speed of __________________

M: Italian inventor of radio __________________

R: used to pick up radio signals __________________

S: a type of code that uses flags __________________

T: selects one radio signal __________________

W: radio signals travel as __________________


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Unit 2: Telecomms Radio quizzes Lesson 6: extra

Clues across Clues down

1. 300 million metres per second. 2. Radio waves carry _______.

4. Part of the radio that picks up 3. What this unit is about.

radio waves.

4. Short for amplitude modulation.

5. Hz stands for _________.

6. Radio signals travel as ______ .

7. 24 hours.

7. Part of a radio or someone who

9. Invented by Marconi. unscrambles?

10. It picks up radio signals. 8. There are 86,4000 ________

in a 7 across.

11. Used to select different stations.

12. Youll usually find a radio in a ___.

13. Converts electrical energy into

sound energy. (Short name.)

1 2 3

4

5

6

7 8 9

10

11 12

13


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Unit 2: Telecomms The television Lesson 7

The parts of a TVTelevisions seem much more complicated than radios but they

are surprisingly similar in the way that they work. TVs receive

radio waves, just like radios but:

Television signals are radio signals with a higher frequency.What to do - 1

1. Collect a set of TV Cards.

2. Put them together in the right order, then check with your teacher.

4. Copy the diagrams on the cards into these spaces.


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Match the parts to the jobsThe descriptions of all the parts of a TV are on the labels below, but they are

mixed up.

Match each label to the right part, and complete the sentences.

The TV aerial ___________________________________________ The TV tuner ____________________________________________ The sound decoder _______________________________________

________________________________________________________

The picture decoder ______________________________________________________________________________________________

The sound amplifier_______________________________________ The picture amplifier _____________________________________ The loudspeaker _________________________________________

________________________________________________________

The picture tube _________________________________________________________________________________________________

selects one

signal

turns the

electrical

signal into

sound

separates the

sound signal

from the TV

wave

boosts the

sound

signal

picks up all

the TVsignals

boosts the

picturesignal

turns the

electrical

signal intolight energy

separates the

picture

signal fromthe TV wave


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Unit 2: Telecomms How a TV tube works Lesson 7: extra

Pictures from electronsIn a TV tube, tiny particles called electrons are fired at the screen. When they hit

a special paint on the screen, they give off a flash of light. But this is just the

beginning of how a TV tube works.

Watch the demonstration your teacher will show you.

Label the diagram below, the answer the questions.

1. Which part of the TV tube produces the electrons?

2. The TV tube has no air in it a vacuum. Why is this?

3. How is the electron beam moved up and down the screen?

4. When the beam is moving very quickly, the dot turns into a line. Why is

this?


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Unit 2: Telecomms How a TV tube works Lesson 7: extra

Getting the coloursIn a colour TV, there are three types of paint on the screen. One gives off red

light, one gives off green light and one gives off blue light.

Mixing red, green and blue light produces all the colours seen on aTV screen

What to do

1. Collect a ray-box kit, a screen and a power supply.

2. Put the three-colour filter into the ray-box, then plug in to the power

supply.

3. Use a pencil or a piece of card to block the red ray of light.

4. Move the screen back until the green and blue rays mix. What colour do

you see?

5. Now block the green ray of light. What colour do you see when red and

blue mix?

6. Block the blue ray. What colour do you see when red and green mix?

7. Dont block any of the colours. What do you see when red, green and blue

all mix?

Red and blue light combine to give __________. Red and green light combine to give _________ .

Blue and green light combine to give __________.

Red and blue and green light combine to give _________.R

G B

Y MW

C


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Unit 2: Telecomms Satellites Lesson 8

Communications from spaceIn 1957, Russia launched the first satellite. It was called

Sputnik. Sputnik did prove that satellites could orbit the Earth

But it didnt do very much else. People realised that satellites

could be used for communication. They realised that signalscould be sent up to the satellite, which could then send them back down to a

different place on the Earths surface.

In 1962, the satellite Telstar was launched from Cape Canaveral.

Telstar took about two hours to orbit the earth. It only travelled a

few thousand kilometres above the surface. This meant that

communications were only possible for about 20 minutes as it

passed overhead. Nevertheless, the first TV pictures were sent

between America and Britain. Within a few years, many more satellites had

been launched. Satellites were used to send telephone calls as well as TV

signals.

For satellites to be really useful, we must be able to communicate with them all

the time not just when they pass overhead. The higher a satellites orbit, the

longer it takes to go round the Earth. At 36,000 kilometres above the

Earths surface, a satellite takes 24 hours to make an orbit. Because

the Earth turns round once every 24 hours, the satellite stays above

the same point on the Earths surface. These types of satellites are

called geostationary. The first geostationary satellite, Early Bird,was launched in 1965.

1. Sputnik didnt do very much. Why was it useful?

2. Why was Telstar not very useful for communication?

3. How does the time taken for a satellite to orbit depend on its height above

the Earth?

4. Complete this key point.

A g____________ satellite stays above the s_____ p_____ on theEarths surface.


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Why are satellite dishes curved?If you have a satellite dish at home, youll know that its

shaped a bit like a bowl. The huge dishes used to send signals

up to satellites have the same sort of shape. Why is this?

What to do

1. Collect a ray-box with a triple slit, a power supply and a curved mirror.

2. Set up the ray box with the triple slit and plug in to the power supply.

3. Slide the bulb along the ray-box until the three rays are parallel.

4. Shine the three rays against the curved mirror.

5. Complete this diagram to show what happens to the light rays after they

hit the mirror.

Did you see a particularly bright spot? The light was stronger at this point.

Curved reflectors can do this with other types of signal as well.

A curved reflector on receiving aerials (like a satellite dish) makesthe signal stronger.

Complete this passage to explain why a curved reflector makes signals stronger.

Unlike a normal TV aerial, a curved reflector has a large ______. This means it

can gather more ______.

The curved shape means that all the signals are _______ at a single point.

If a receiver is put at this point, it will pick up a very ________ signal.

Choose some from:strong, area, wavelength, focused, picture, signal.


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Check what youve learntThe questions below cover all the things you should have learnt in lessons 1 - 8.

See how many questions you can answer from memory then read over yournotes and correct any answers you got wrong or missed out.

1. Complete this sentence.

Radio communication does not need ________ between the transmitter

and the receiver.

2. Radio signals are waves which transfer ________?

3. What speed do radio waves travel at?

4. Name the 5 parts of the radio, in the correct order.

5. What does the aerial do?

6. What does the tuner do?

7. What does the amplifier do?

8. What does the loudspeaker do?

9. What unit is used to measure frequency?


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Unit 2: Telecomms Review Lesson 8: extra

10. How can you identify a radio station?

11. How are TV signals different to radio signals?

12. What does the picture decoder in a TV do?

13. What does the sound amplifier in a TV do?

14. How does a TV tube work?

15. What colour do you get if you mix red light and blue light?

16. What colour do you get if you mix red, green and blue light?

17. What is a geostationary satellite?

18. Why are satellite dishes curved?

My score out of 18: ____


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Unit 2: Telecomms Reflecting light Lesson 9

Bouncing lightComplete this diagram to show what happens when a light ray hits a mirror.

Light can be reflected.But light can be reflected in other ways.

What to do

1. Collect a ray box, a power supply and a semi-circular block of perspex.

2. Put the semi-circular block on the diagram below. Dont worry if its a

different size.

3. Set up your ray box to produce a single narrow beam of light.

4. Shine the light along ray 1.

5. On your diagram, draw what happens to the ray of light.

6. Repeat for rays 2 and 3.

What happened to ray 3?

1

2

3


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Total internal reflectionWhen a ray of light hits the inside of a piece of glass at a big enough angle, the

glass acts like a mirror. The ray of light is reflected inside the glass. This is

called total internal reflection.

What to do

1. Collect a curved perspex rod.

2. Use your ray-box to shine a ray of light into one end of the piece of

perspex.

3. Complete this diagram to show what happens to the ray of light.

If you have a long piece of glass or perspex, you can bounce light all the way

along it using total internal reflection

This idea is used to make optical fibres. Your teacher will show you some

optical fibres.


An optical fibre is a long thread of very pure g_______. Light travels along an optical fibre by t______ __________

_______________.


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Optical fibres can be used to guide _______ from one place toanother.


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Unit 2: Telecomms Optical fibres Lesson 9: extra

Video questionsWatch the video about optical fibres. Afterwards you will try to answer the

questions below. Then we will watch the video again to complete the sheet.

1. How fine is the glass thread at the start of the video?

2. What does the triangular prism do?

3. How was light used to send messages in the past?

4. What is the name of the angle when the light grazes the edge of the

semi-circular block of glass?

5. Why could optical fibres not be made in 1960?

6. Why is glass green when you look at it edge-on?

7. Why is optical fibre made with a second layer of glass?

8. What type of lasers are used for optical communication?

9. What is optical fibre made from?


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Using light to send soundYour teacher will show you an experiment where an optical fibre is used to send

music from one side of a desk to the other.

What to do - 1

Watch the experiment. In the box, draw and label a diagram of the experiment.

Use these labels.

laser radio laser beam receiver optical fibre

What to do - 2Complete this passage to describe how the system works.

The ______ produces a narrow beam of _______. A music signal from a tape-

player is used to _________ or change the ________ of the laser beam.

The beam then travels down an __________ fibre. It travels down it like this:


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When the beam reaches the __________, a detector picks up the l______ signal

and converts it back into a s_______ signal.

Choose from:

optical sound light laser modulate

light receiver brightness


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Unit 2: Telecomms Optical fibres in the home Lesson 10

Glass revolutionRead the passage, the complete the key points and questions.

Twenty-five years ago, most homes only had one phone. There were only three

television channels. Only big companies had computers. The Personal

Computer (PC) wasnt even an idea. Fax machines were rare. The internet had

just begun, but it was only used for very specialist purposes.

The last ten or twenty years have been called the Information Age. We are all

bombarded with information every day. There are loads of TV channels, mobile

phones that are never quiet, text messages, e-mail. This huge increase in the

sending of information has needed a complete change in technology.

This is where optical fibres come in. Today, many telecommunications linksinto the home are by optical fibres. An optical fibre can carry a huge amount of

information. In an optical fibre, flashes of light travel down threads of glass at

almost 200 million metres per second. A typical home may have cable TV,

telephones, internet and e-mail all supplied by optical fibres.

Optical fibres have several advantages. They carry huge amounts of information.

They are cheap (because theyre made from sand). They dont get interference,

and they are almost impossible to tap. One disadvantage of using optical fibres

to deliver information to the home is that streets have to be dug up to lay cables.This can cause a lot of disruption.

Optical fibres transmit l_____ signals. Signals in optical fibres move at a speed of ___________________. Telecommunications services that are brought into the home by

optical fibres include:

* _________________

* _________________

One advantage of optical fibres is ___________________________________________________________________________________.

One disadvantage of optical fibres is _________________________


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Unit 2: Telecomms Optical fibres in the home Lesson 10

________________________________________________________.

Speedy signalsAlthough light signals in optical fibres travel very fast, they are not as fast as

light signals in air. The speed of light in air is 300 million (300,000,000)metres per second.

The speed of light in an optical fibre is 200 million (200,000,000)metres per second.

Use these key points to answer these questions.

1. How far can light travel in air in 5 seconds?

2. How far can light travel in an optical fibre in 5 seconds?

3. A beam of light X is sent through the air. At exactly the same time, abeam of light Y is sent down an optical fibre.

a) Which one will be in the lead after 3 seconds?

b) How far ahead will it be?

4. Scientists plan to install an optical cable from the Earth to the Moon. The

Moon is 450,000,000 metres away from Earth.

a) How long will it take a laser beam to travel along this cable?

b) How long would it take if the laser beam was fired through the air?


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Unit 2: Telecomms Optical illlusions Lesson 10: extra

Now you see itWhether light travels through the air or through an optical fibre, its not that

difficult to fool the brain. Can you sort these out?

A man in a canoe fishing? Or a big bird

upside-down?

Try counting the white circles. And how

many black circles?

Look at the dot in the centre and move

your head backwards and forwards.

Are two heads better than one?

Which line is longer?


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Unit 2: Telecomms Optical illlusions Lesson 10: extra

An Eskimo looking into a cave or not?

Are the horizontal lines level?

How many legs has the elephant

got?

Duck or rabbit?

Stare at the black dot. What

happens to the grey mist?A skull or a woman at a mirror?


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Unit 2: Telecomms The telephone Lesson 11

Phones everywhereIn the last 100 years or so, phones have changed tremendously. They used to be

large, heavy and only a few people owned them. Now phones are small and

getting smaller. Theyre digital, theyre mobile, they play games. Soon, youllhave a mobile phone built into the skin on your arm.

But all phones work in basically the same way.

In a telephone, messages are sent out by a transmitter and pickedup by a receiver.

What to do

1. Try out the model phones that your teacher has set up.

2. Whistle a low-pitched note into the phone, then a high-pitched note. What

patterns do you see on the oscilloscope?

3. How did the signal change?

Low pitch sound High pitch sound


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Unit 2: Telecomms The telephone Lesson 11

4. Whistle a loud note into the phone, then a quiet note. What patterns do

you see on the oscilloscope?

5. How did the signal change?

How is the signal sent?Different types of phones send messages in different ways. Electrical currents,

flashes of laser light and radio waves can all be used to send telephone signals.


Telephones can use e___________ signals. These travel alongm_______ wires at a speed of almost 300 million metres per

s________.

Telephones can use l_______ signals. These travel alongo________ f________.

Mobile phones send signals as r_______ waves through the a___.

Louder sound Quieter sound


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Unit 2: Telecomms Telephone history Lesson 11: extra

Video questionsWatch the video The Secret Life of the Telephone.

Answer these questions as you watch the programme.

1. About when was the telephone invented?

2. Before telephones, what were electromagnets first used for?

3. Who invented the first telephone?

4. Why did his family emigrate to the USA?

5. What was the name of his assistant?

6. On a modern telephone, what is the diaphragm made from?

7. Who patented the improved microphone?

8 What type of granules were used in the improved microphone?


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Unit 2: Telecomms Telephone history Lesson 11: extra

9. How did telephone companies persuade people to buy telephones?

10. What was the horse-collar phone used for?

11. Why were male telephone operators not used?

12. Why was Strowgers rival undertaker doing such good business?

13. Why are Strowger exchanges called click and bang?

14. What electronic device, invented in 1947, replaced mechanical switches?

15. How did Shockley disgrace himself?

16. Digital exchanges have reduced failed connections from 5% to ?

17. Why was a kitchen phone so unusual?


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Unit 2: Telecomms Sending and receiving Lesson 12

All-in-oneIn early telephones, you spoke into one part of the phone and

listened to a separate part. In all modern phones, the handset does

both jobs.

Use these words to label this handset:

earpiece mouthpiece microphone loudspeaker


The m______________ of a phone is a transmitter and it containsa m______________.

The e_____________ of a phone is a receiver and it containsa l_______________ .

What to do - 1

1. Collect a telephone handset.

2. Take it apart (you may need a screwdriver).

3. See if you can identify the microphone and the loudspeaker.


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Unit 2: Telecomms Sending and receiving Lesson 12

What to do 2

1. Think about the energy changes that take place when you speak to

someone on the phone.

a) What happens to the sound energy of your voice?

b) What type of energy travels along the wire?

c) How fast do you think the signal travels along the wire?

d) What happens at the loudspeaker?

2. Use your answers to help you label this diagram.

3. Complete these key points. In a microphone, _________ energy is turned into ____________energy.

In a loudpeaker, __________ energy is turned into _________energy.

A telephone signal travels along metal wires at a speed of almost_____________________ metres per second.


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Unit 2: Telecomms Pictures by phone Lesson 12: extra

Getting your fax rightTodays mobile phones can send photos easily enough. But to send documents

or detailed diagrams over the phone, you need a facsimile machine (fax for

short).

Fax is the name given to sending documents by telephone.How fax works

1. You need to work with a partner. One of you is the sender, one of you is

the receiver.

2. If you are the sender, collect Info Card 2.12.

3. If you are the receiver, use the blank grid below.

4. The senders instructions are on the Info Card.

5. If you are the receiver:

work across the grid from left to right, row by row

if your partner says blank, leave the square blank

if your partner says fill, colour in the square.


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Unit 2: Telecomms Pictures by phone Lesson 12: extra

How fax works (continued)A real fax machine scans a page, breaking it into thousands of tiny boxes. It

detects whether the box is black or white, and sends that information down the

phone line.

The fax that receives the information then prints the page, tiny square by tiny

square. It either fills the squares in black, or leaves them blank.

If you look at a fax document carefully, you can sometimes make out the edges

of the tiny squares.

Choosing a fax

Use this page from a fax machine brochure to answer the questions.

Model

number

Pages per

minute (send)

Pages per minute

(receive)

Cost of toner

cartridges ()

Price ()

A400 4 12 22 215

A650 6.5 8 18 299

A700 7 8 27 350

A1000 10 9 20 419

1. The Arcol Company needs a new fax. They dont send many faxes, butreceive a lot from clients. Which fax should they choose and why?

2. Dave decides to buy the A700 as its a bit faster than the A650. Joe tells

him its a bad decision. Who is right and why?

3. The A650 uses 6 toner cartridges a year. How much will it cost to buy an

A650 and run it for three years?

4. A new fax is introduced which can send 15 pages per minute. What is its

model number?


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Unit 2: Telecomms Phones on the go Lesson 13

Mobile maniaTwenty years ago, the mobile phone didnt exist. Fifteen

years ago, they were the size (and weight) of a brick and

cost about 3000. Ten years ago, they started to take off and now theyre everywhere.

Mobile phones use very different technology to normal phones especially in

how the signals are sent.

What to do - 1

1. You need two mobile phones and a microwave detector.

2. Switch on the microwave detector. The red LED will come on for a

couple of seconds.

3. Put one of the phones next to the microwave detector.

4. Ring the phone from the other mobile. Dont answer the call.

What happens?

What to do 2

Ring the phone again. Gradually move the phone away from the detector.

How far can you move the phone before the red LED goes off?

Mobile phones send signals by microwaves, which are a type of radio wave.

These waves travel through the air at the speed of light: 300 million metres persecond. The microwaves are particularly strong during the handshake this is

when two mobile phones are linking together.

Mobile phones are really small microwave radios. When you speak on a mobile

phone, the message is transmitted as microwaves. When you listen on a

mobile, the message is being received as microwaves.

Complete this key point:


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A mobile phone acts as a radio t____________ and a radior___________.

Mobiles bad for the brain?

Over the last few years, there have been stories in the press about how mobile

phones or the microwaves they use may be damaging to health. Read these

two articles written by people with different points of view.

Article A

Turn over for article B

Everyday you hear about mobile phones frying your brain andits all nonsense. Its true that mobile phones emit microwave

radiation but so do microwave ovens and satellite transmitters,

and nobody worries too much about those. Microwaves certainly

do heat things up and studies show that using a mobile phone

could raise the temperature of your brain by 0.1 degrees Celsius.

That seems worrying until you realise that jogging raises the

temperature of your brain by 1 degree Celsius.

What a lot of people forget is how many lives mobile phones have

saved. Think of the people who have accidents in remote parts of

the country. In the past, they could die before anyone knew

anything was wrong. Now theyre just a phone call away from help.

Kids who miss the last bus can phone home, rather than walking

back in the dark. Everyone is in touch all the time and that

keeps everyone safer. I know mobiles can be irritating Im sickof hearing them go off when Im at the cinema or in a restaurant

but Im happier knowing that my daughter can get in touch with

me any time she needs.


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Article B

Which article do you agree with and why?

Which article seems to be the most scientific? Explain your answer.


One advantage of mobile phones is:

If you think mobile phones are just a handy way of staying in

touch, try living next to a mobile phone mast. Since they put a

mast up just a hundred metres from my house, Ive never been

right. I seem to get ill all the time, I feel depressed and its

affecting my family. My wee boy hes thirteen now used to be

full of life. Now hes quiet and moody and Im worried theres

something serious wrong with him. My friend told me how heraunt got cancer from using her mobile too much. I wont let my

kids have a mobile. Its hard, because all their friends have them

but youve got to look after their health.

I mean, lets face it, these things use microwaves. Have you seen

what microwaves will do to a piece of meat? It cant be right to

do that to your brain. And theres people out there who drive

while theyre using mobiles how many car crashes and deathshas that caused? We coped OK before mobile phones. Im sure

we can cope well enough without them.


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One disadvantage of mobile phones is:


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Check what youve learntThe questions below cover all the things you should have learnt in lessons

9 - 13.

See how many questions you can answer from memory then read over your

notes and correct any answers you got wrong or missed out.

1. Complete this sentence:

Optical fibres work by t____________ i____________ r____________.

_

2. What are optical fibres made from?

3. What speed does light travel at in an optical fibre?

4. How far would light travel along an optical fibre in 0.25 s?

5. Name two services that optical fibres can bring into the home.

6. Give one advantage and one disadvantage of optical fibres.

7. Who invented the telephone?

8. Complete the following sentence:

In a telephone, messages are sent out by a t_______________ and picked up by

a r_______________.


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9. Draw a sketch of a) a loud, high frequency signal

b) a quiet, low frequency signal

10. What is the speed of electrical signals along metal wires?

11. Where in a phone do you find a microphone?

12. Where in the phone do you find a loudspeaker?

13. What is the energy change in a microphone?

14. What is the energy change in a loudspeaker?

15. What is fax short for?

16. What type of waves do mobile phones use?

18. Give an advantage and a disadvantage of mobile phones.

Telecommunications Unit - Lessons

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