Telecommunication 1.1 – Communication Using Waves.

Telecommunication

1.1 – Communication Using Waves

Sound and Light Energy

Sound and light are important types of energy.

We use them to transmit (send) signals from one place to another.

This is known as communication.

Transmitting (sending) signals over a long distance is known as telecommunication.

Activity 1 – Sound and Light Energy

For each case, record:

1. the type of energy used

2. a short description of how the energy is used to communicate

Example

Light – used to communicate with pedestrians when it is

safe to cross the road.

Sound – used to have a conversation.

Sound – used to transmit (send) signals over long distance

A

B

Sound – used to indicate start of a race.

Sound – used to attract attention or start/stop sport.

C

D

Sound – used to raise alarm or signal school periods.

Sound – used to start races or stir a crowd at sports event.

E

F

Light – used to communicate with other ships

Light – use to communicate emergency situation

G

H

Light – used to warn ships of land.

Light – used to warn people of an emergency vehicle

I

J

Light – used to communicate with motorists

Light – used to allows motorists to communicate with one another

K

L

Speed of Sound and Light

In air, speed of sound is: 1ms 340

In air, speed of light is: 18 ms 103

Use the word bank to complete the passage below.

hear less light light

lightning

see sound

immediately

thunder

During a storm, thunder and lightning are produced at exactly the same time.

We the before we the

because in air the speed of is than the speed

of .

The travels so fast it reaches us almost .

hearsee lightning

thunder

sound

light

light immediately

less

Tutorial 1 – Speed of Sound and Light in Air

1. At a fireworks display, a rocket explodes high above your head, producing a loud explosion and a bright flash of light at the same time.

(a) What will reach you first – sound of explosion or flash of light?

(b) Explain why.

2. On a golf course, you observe a golfer in the distance hitting a golf ball with her club.

(a) What will you observe first – the ball moving through the air or

the sound of the club hitting the ball?

(b) Explain why.

1. At a fireworks display, a rocket explodes high above your head, producing a loud explosion and a bright flash of light at the same time.

(a) What will reach you first – sound of explosion or flash of light?

(b) Explain why.

Answer

(a) The flash of light will reach you before the sound of the explosion.

(b) The flash of light reaches you before the sound of

the explosion because the speed of light in air is much greater than the speed of sound in air.

2. On a golf course, you observe a golfer in the distance hitting a golf ball with her club.

(a) What will you observe first – the ball moving through the air or

the sound of the club hitting the ball?

(b) Explain why.

Answer

(a) The golf ball moving through the air will be observed first.

(b) The golf ball moving through the air is observed

first because the speed of light in air is

much greater than the speed of sound in air.

Distance, Time and Speed

t vd

x

÷d

v t

We can use this relationship (formula) to solve problems about sound travelling through the air (or even other materials).

distance

unit: m

time

unit: s

speed

unit: ms-

1

Example 1

How long will it take a sound wave to travel a distance 1.5 km?

km 1.5d

-1ms 340v

?t

vd

t

3401,500

t

s 4.41t

When answering calculation questions, show all working and use the layout shown.

m 1,500

Tutorial 2 - Distance, Time and Speed of Sound Calculations

1. Calculate the distance sound will travel through the air in 2 s.

2. How far will the sound of an explosion travel through the air in 5 s?

3. Calculate the time it will take sound to travel 1,020 m through the air.

4. How long will it take the sound of a bell to travel 850 m through the air?

5. Calculate the speed of sound in air if it takes 4 s for the sound to travel 1.36 km.

6. The sound of a car horn is heard 1.19 km away, 3.5 s after it has been sounded. Calculate the speed of the horn sound in air.

7. Susan shouts at a brick wall. After 0.8 s she hears an “echo” – the sound of her shout reflected off the wall.

Calculate how far away from the wall Susan is.

BE CAREFUL! – It might help if you draw the path taken by the sound on the diagram.

Sound has a different speed in different materials.

1-

1

ms 1,500 water in sound of speed

ms 5,200 steel in sound of speed

** Do not need to remember these values **

8. A steel wire is 6.76 km long. Calculate the time it will take sound to travel along the wire.

9. To find the depth of water beneath its hull, a fishing boat sends a pulse of sound through the water from its hull to the sea bed.

After 1.2 s, the fishing boat detects the sound pulse reflected from the sea bed.

How deep is the sea?

1. Calculate the distance sound will travel through the air in 2 s.

s 2t -1ms 340v

?d

tvd

2340d

m 680d

2. How far will the sound of an explosion travel through the air in 5 s?

s 5t -1ms 340v

?d

tvd

5340d

m 1,700d

3. Calculate the time it will take sound to travel 1,020 m through the air.

4. How long will it take the sound of a bell to travel 850 m through the air?

m 1,020d-1ms 340v

?t

vd

t

3401,020

t

s 3t

m 850d-1ms 340v

?t

vd

t

340850

t

s 2.5t

5. Calculate the speed of sound in air if it takes 4 s for the sound to travel 1.36 km.

s 4t

km 1.36d

?v

td

v

41,360

v

6. The sound of a car horn is heard 1.19 km away, 3.5 s after it has been sounded. Calculate the speed of the horn sound in air.

s 3.5t m 1,190

?v

td

v

3.51,190

v

-1ms 340v

-1ms 340vm 1,360

km 1.19d

7. Susan shouts at a brick wall. After 0.8 s she hears an “echo” – the sound of her shout reflected off the wall.

Calculate how far away from the wall Susan is.

BE CAREFUL! – It might help if you draw the path taken by the sound on the diagram.

transmitted sound

reflected sound

s 0.8t -1ms 340v

?d

tvd

0.8340d

m 272d

m 136d

sound travels to the wall and back

distance from the wall is only half of this distance

8. A steel wire is 6.76 km long. Calculate the time it will take sound to travel along the wire.

m 6,760-1ms 5,200v

?t

vd

t

5,2006,760

t

s 1.3t

km 6.76d

9. To find the depth of water beneath its hull, a fishing boat sends a pulse of sound through the water from its hull to the sea bed.

After 1.2 s, the fishing boat detects the sound pulse reflected from the sea bed.

How deep is the sea?

sound transmitted

sound reflected

s 1.2t -1ms 1,500v

?d

tvd

1.21,500d

m 1,800d

m 900d

sound travels to the seabed and back

depth of seabed is only half of this distance

Measuring Speed of Sound

We can perform an experiment to measure the speed of sound in air.

microphone Bmicrophone Ahammer and metal plate

distance (1m)

electronic timer

The distance between the two microphone is measured using a metre stick.

A sharp noise is made near microphone A.

The time taken for the sound to travel between A and B is measured using an electronic timer.

The speed of sound is calculated using:

smicrophone between travel to sound for timesmicrophone between distance

v

Results

MeasurementTime (micro

seconds)

12345

Average

Calculation

1. (a) What value for the speed of sound in air do you obtain?

(b) How could you improve the experiment?

Answer

(a)

(b)

s t

m 1d

?v

td

v

-1ms v

v

Scientific Prefixes

Prefix Symbol FactorScientific Notation

kilo k x 1,000 x103

mega M x 1,000,000 x106

giga G x 1,000,000,000 x109

milli m 1,000 x10-3

micro μ 1,000,000 x10-6

nano n 1,000,000,000 x10-9

Tutorial 3 – Scientific Notation and Prefixes

Yellow Book

Basic Mathematics - Page 1

Q1, 3, 4, 5, 6 and 7

Answers

1. (a)

(b)

(c)

(d)

(e)

(f)

8103.70370,000,00 10102.005,00020,050,000

14102.0050,000,000930,000,00 -4102.30.000,23

-8106060.000,000, -11104000,040.000,000,

3. (a)

(b)

(c)

(d)

(e)

(f)

V 105kV 5 3

V 1023mV 23 -3

V 107μV7 -6

V 102.8MV 2.8 6

V 1067nV67 -9

V 10389μV 389 -6

4. (a)

(b)

(c)

(d)

(e)

(f)

MJ 8J 108J 8,000,000 6

μJ 4J 104J 0.000,004 -6

kJ 6.34 J 106.34J 6,340 3

mJ 5J 105J 0.005 -3

μJ 63J 10630.000,063 -6

MJ 9.806J 109.806J 9,806,000 6

5. (a)

(b)

(c)

(d)

(e)

(f)

m 1050km 50 3

m 1030,000km 30,000 3

m 1057mm57 -3

m 109cm 9 -2

m 108.31km 8.31 3

m 25,356.28

m1028 m 356m 1025cm 28 m 356 km 25 -2-3

6. (a)

(b)

(c)

(d)

(e)

(f)

s 300560min 5

s 10,80036060hours 3

s 16040260s 40 min 2

s 50222860s 22 min 8

s447 7.4560min 7.45

s 26,73030256076060s 30 min 25 hours7

7. (a)

(b)

(c)

(d)

kg 0.5g 100.5g 500 3

kg 7,400g 107,400g 7,400,000 3

kg 0.000,250g100.000,250mg 250 3

kg 0.0975g 100.0975g 97.5 3

Light

Light is the fastest thing there is - nothing can travel faster than light!

Since light travels so fast, we see things happen immediately. This lets us calculate how far away we are from an event taking place.

The time between us seeing something happen and hearing it happen is the time it takes for the sound to reach us.

Because we know the speed of sound in air, we can apply the formula: t vd

Tutorial 4 - Distance, Time and Speed of Light Calculation

1. During a storm, thunder and lightning are produced at exactly the same time.

(a) You see a flash of lightning. After 5s, you hear the thunder. How far away from you is the storm?

(b) A while later, you see another flash of lightning – but, this time, you hear the thunder after only 1.5 s. How far away from you is the storm now?

2. You see a flare exploding in the distance. After 3.5 s you hear the sound from the explosion.

How far away from you was the flare when it exploded?

3. A soldier sees a shell explode. The sound from the explosion reaches him 0.2 s later.

How far away from the soldier did the shell explode?

1. During a storm, thunder and lightning are produced at exactly the same time.

(a) You see a flash of lightning. After 5s, you hear the thunder. How far away from you is the storm?

(b) A while later, you see another flash of lightning – but, this time, you hear the thunder after only 1.5 s. How far away from you is the storm now?

s 5t -1ms 340v

?d

tvd

5340d

m 1,700d

s 1.5t -1ms 340v

?d

tvd

1.5340d

m 510d

(a)

(b)

2. You see a flare exploding in the distance. After 3.5 s you hear the sound from the explosion.

How far away from you was the flare when it exploded?

s 3.5t -1ms 340v

?d

tvd

3.5340d

m 1,190d

3. A soldier sees a shell explode. The sound from the explosion reaches him 0.2 s later.

How far away from the soldier did the shell explode?

s 0.2t -1ms 340v

?d

tvd

0.2340d

m 68d

Waves and Energy

Water waves on the sea or a pond are easy to see.

All waves transfer (carry)

g from one place to another.

A tsunami sea wave transfers an enormous amount of which can cause extensive damage when the wave reaches land.

energy

energy

Waves & Signal Transmission

Sound and light signals are transmitted (sent)

from one place to another by g .

also transmit signals for:

waves

Waves

radio television

mobile phones

satellites

Wave Diagrams

The diagram below represents a typical wave when viewed from the side.

Use the word bank to complete the diagram.

amplitude

wavelength

amplitude

crest

wavelength

trough

crest

trough

wavelength (λ)

amplitude

amplitude

wavelength (λ)

amplitude

wavelength

amplitude

crest

wavelength

trough

These diagrams represent waves viewed from above. The

lines show the middle of wave crests. No wave troughs are shown.

On each diagram show the wavelength.

straight waves

circular waves

λ

λ

Describing Waves

Use the word/symbol bank to complete the table.

above

distance

amplitude

amplitude

second wavelength

below

f Hz λ m m ms-

1

v

Quantity Symbol Unit Description

wave crest part of wave central line

wave trough part of wave central line

( )

height of wave crest or wave trough measured from the centre line

the higher the of a wave, the more energy it carries

lambda ( )

( )

distance between two identical neighbouring points on a wave, e.g. distance between two neighbouring

crests

frequency ( ) ( )number of wavelengths (or crests or

troughs) per .

speed ( ) ( ) wave travels every

second

period T s time taken to produce one wave

above

below

amplitude

second

distance

λ

Hz

wavelength

amplitude

ms-

1

m

m

f

v

The frequency of a wave is:

number of whole waves produced in one second

This can be represented by the formula:

tN

f

x

÷N

f t

number of waves

unit: NONE

time

unit: s

frequency

unit: Hz

The speed of a wave is:

distance travelled by a wave in one second

This can be represented by the formula:

t vd

x

÷d

v t

distance

unit: m

time

unit: s

speed

unit: ms-

1

Tutorial 5 – Water Wave Calculations

1. (a) Which of these waves is carrying the most energy?

(b) Explain your answer.

2. The wave shown is travelling to the right.

(a) As the wave travels, what happens to its amplitude?

(b) What must be happening to the waves energy?

A B

3. (a) State the value for this wave’s:

(i) amplitude (ii) wavelength

0

0.2

0.4

0.4 0.8 1.2 1.6

(metres)

(metres)

(b) This wave was produced in 1 second. State the value of its frequency.

4. Determine the frequency of the wave in each case.

(a) 5 wavelengths are produced every second.

(b) 10 water waves pass the end of a pier in 2 seconds.

(c) 12 circular waves spread across a pond in 20 seconds.

5. (a) For this wave, state the value of:

(i) the amplitude(ii) the wavelength

0.8 m

0.2 m

(b) The wave is produced in 2 seconds. State the value for its frequency.

6. (a) Determine the wavelength of these water waves.

(b) These five wave crests were produced in 25 seconds. Determine the frequency of the waves.

20 m

7. (a) What is the wavelength of these circular water waves.

(b) The three wave crests were produced in 0.5 seconds. What is the wave frequency?

6 m

8. A tsunami sea wave takes 6 s to travel up a beach with a speed of 15 ms-1. What distance does the wave travel up the beach?

9. When Sajidha threw a stone into a pond, circular waves travelled 7.5 m across the water in 2.5 s.

Calculate the speed of these water waves.

10.Sea waves approach a cliff at 4 ms-1. What time will the waves take to travel 20 m?

11.Sid the surfer rides the crest of a sea wave travelling at 6 ms-1 for 8 s. Calculate how far the wave carries Sid in this time.

12.A drop of water from a leaking tap causes waves on the surface of Brenda’s bath water.If these waves travel 0.4 m in 1.6 s, at what speed are they travelling?

13.As the tide goes out, sea waves travel 50m with a speed of 2.5 ms-1.How long do the waves take to travel this distance?

The Wave Formula

The time taken for one wave to be produced is the

period.

The frequency and period of a wave are related by:

One complete wave (1λ) is produced in a time of one period (T).

This wave will travel a distance (d) of one wavelength (1λ) in a time of one period (T).

T1

f

td

v

Tλ 1

v

λT1

v

λfv

wave will travel one whole wavelength (1λ) in the time it takes to produce one whole wave (the period – T)

λ fv

x

÷v

f λ

speed

unit: ms-

1

wavelength

unit: m

frequency

unit: Hz

Equivalence of the 2 Wave Formula

Tutorial 6 – Speed, Wavelength and Frequency Calculations

1. Calculate the speed of water waves which have a frequency of 2 Hz and wavelength of 5 m.

2. Calculate the frequency of water waves in a harbour if they travel at 3 ms-1 and have a wavelength of 4 m.

3. Calculate the wavelength of water waves on a pond which travel at 0.75 ms-1 and have a frequency of 1.5 Hz.

4. Every second, two waves are produced on Alan’s bath water by water dripping from a tap. If these waves have a wavelength of 0.05 m, calculate the speed.

5. The wind causes waves to travel across a puddle at 2.4 ms-1. If the waves have a wavelength of 0.6 m, determine their frequency.

6. A wave generator in a swimming pool produces 2.5 waves every second. The waves travel across the pool at 1.2 ms-1. Determine their wavelength.

7. Calculate the speed of sound waves in air which have a frequency of 0.5 kHz and a wavelength of 0.34 m.

8. Calculate the frequency of sound waves in air which have a wavelength of 1.7 m.

9. Calculate the wavelength of sound waves in air which have a frequency of 0.8 kHz.

10.A submarine sends a pulse of sound through the sea. Determine the speed of the sound pulse if it has a frequency of 7.5 kHz and a wavelength of 0.2 m.

11.Sound travels through steel at 5,200 ms-1. In the steel, sound waves have a wavelength of 2m. Calculate the frequency.

12.Ultrasound (frequency of 21 kHz) travels through human muscle at 1,600 ms-1. Calculate the wavelength of the ultrasound in the muscle.

1. Calculate the speed of water waves which have a frequency of 2 Hz and wavelength of 5 m.

λfv Hz 2f

m 5λ?v

52v 1ms 10v

2. Calculate the frequency of water waves in a harbour if they travel at 3 ms-1 and have a wavelength of 4 m.

λv

f -1ms 3v

m 4λ?f 4

3f

Hz 0.75f

3. Calculate the wavelength of water waves on a pond which travel at 0.75 ms-1 and have a frequency of 1.5 Hz.

fv

λ-1ms 0.75v

Hz 1.5f ?λ 1.5

0.75λ

m 0.5λ

4. Every second, two waves are produced on Alan’s bath water by water dripping from a tap. If these waves have a wavelength of 0.05 m, calculate the speed.

λfv Hz 2f

m 0.05λ?v

0.052v 1ms 0.1v

5. The wind causes waves to travel across a puddle at 2.4 ms-1. If the waves have a wavelength of 0.6 m, determine their frequency.

λv

f -1ms 2.4v

m 0.6λ

?f 0.62.4

f

Hz 4f

6. A wave generator in a swimming pool produces 2.5 waves every second. The waves travel across the pool at 1.2 ms-1. Determine their wavelength.

fv

λHz 2.5f -1ms 1.2v

?λ 2.51.2

λ

m 0.48λ

7. Calculate the speed of sound waves in air which have a frequency of 0.5 kHz and a wavelength of 0.34 m.

λfv kHz 0.5f

m 0.34λ?v

0.34100.5v 3 1ms 170v

Hz 100.5 3

8. Calculate the frequency of sound waves in air which have a wavelength of 1.7 m.

λv

f -1ms 340v

m1.7 λ

?f 1.7340

f

Hz 200f

9. Calculate the wavelength of sound waves in air which have a frequency of 0.8 kHz.

fv

λ

kHz 0.8f

-1ms 340v

?λ3100.8

340λ

m 0.43λ

Hz 10 0.8 3

10.A submarine sends a pulse of sound through the sea. Determine the speed of the sound pulse if it has a frequency of 7.5 kHz and a wavelength of 0.2 m.

λfv kHz 7.5f

m 0.2λ?v

0.2107.5v 3 1ms 1,500v

Hz 107.5 3

11.Sound travels through steel at 5,200 ms-1. In the steel, sound waves have a wavelength of 2m. Calculate the frequency.

λv

f -1ms 5,200v

m 2λ

?f 25,200

f

Hz 2,600f

12.Ultrasound (frequency of 21 kHz) travels through human muscle at 1,600 ms-1. Calculate the wavelength of the ultrasound in the muscle.

fv

λ

kHz 21f

-1ms 1,600v

?λ31021

1,600λ

m 0.08λ

Hz 10 21 3