BTEC Applied Science

Bridging pack

Section 3

Waves in

communication

1. Wave definitions https://a-levelphysicstutor.com/wav-wave-props.php https://www.bbc.co.uk/bitesize/topics/zcwkgdm

What is a wave?

Find definitions for the following: Wavelength Amplitude Period Frequency Rest position Displacement

2. Period and frequency

On a displacement-time graph of a wave, period can be found by noting the

time taken for one complete wave.

Amplitude can be read from the maximum height reached on the y-axis

On a displacement-distance graph of a wave, wavelength can be found by

noting the distance for one complete wave

displacement

displacement

period

wavelength

Label the amplitude and wavelength for each of the waves below. Once you have done this, answers the questions at the bottom of the worksheet in your book.

Which of the above waves has: The highest frequency? The shortest wavelength? The largest amplitude? The longest wavelength?

The lowest pitch? The loudest intensity? The smallest amplitude?

A

B

C

D

E

3. Transverse and longitudinal waves

https://www.bbc.co.uk/bitesize/guides/z9bw6yc/revision/1

Find a definition for these two types of

waves:

Transverse waves

Longitudinal waves

Label and name these waves

4. Using the wave formula: wave speed, frequency and wavelength

v = f × λ v speed (metres per second, m/s)

λ wavelength (metres, m)

f frequency (hertz, Hz)

1. Calculate the wave speed (in m/s) for the following waves:

a) A sound wave in steel with a frequency of 500 Hz and a wavelength of 3.0 metres.

b) a ripple on a pond with a frequency of 2 Hz and a wavelength of 0.4 metres.

c) A radio wave with a wavelength of 30 m and a frequency of 10,000,000 hertz.

2. Calculate the wavelength (in metres) for the following waves:

a) A wave on a slinky spring with a frequency of 2 Hz travelling at 3 m/s.

b) An ultrasound wave with a frequency 40,000 Hz travelling at 1450 m/s in fatty tissue.

c) A sound wave with frequency 440 Hz travelling at 340 metres per second in air.

3. Calculate the frequency (in Hz) for the following waves:

a) A sound wave of wavelength 10 metres travelling at 340 metres per second in air.

b) A wave on the sea with a speed of 8 m/s and a wavelength of 20 metres.

c) A microwave of wavelength 0.15 metres travelling through space at 300,000,000 m/s.

Worked example: Q: A sound wave of frequency 220 Hz travels at a speed of 340 m/s in air.

What is its wavelength?

A: Wavelength, λ = v ÷ f = 340 220 = 1.55 m

(If the wave speed is in metres per second and the frequency is in hertz, the

wavelength will be in metres)

f = v ÷ λ

λ = v ÷ f

The anatomy of a wave

Symbol: Unit: The _____________ of a wave is the maximum displacement

of a point on a wave away from its undisturbed position.

Symbol: Unit: The _______________ of a wave is the distance from a point on one

wave to the equivalent point on the adjacent wave.

Symbol: Unit: The _____________ of a wave is the number of waves passing a

point each second.

Symbol: Unit: The ______________is the speed at which the energy is

transferred (or the wave moves) through the medium.

Peak Trough

Frequency = no. waves per

second time

v =ƒλ

Wave speed = distance time

or

Refraction

https://www.bbc.co.uk/bitesize/guides/zw42ng8/revision/2

What is refraction?

When does it happen?

What causes it to happen?

https://www.explainthatstuff.com/fiberopti

cs.html

What are optical fibres?

How do they work?

What are they used for?

https://www.explainthatstuff.com/endosco

pes.html

What is an endoscope?

How do they work?

What are they used for?

Refraction

1. James shone a ray of light at a mirror as shown below:

He measured the angle of reflection for different angles of incidence.

His results are shown below:

Angle of incidence (⁰) 30 40 50 60 70

Angle of reflection (⁰) 30 40 50 65 70

(a) Which angle of reflection was not measured accurately?

................. ⁰ 1 mark

How can you tell this from this table?

.........................................................................................................................................

.........................................................................................................................................

Incident ray

Reflected ray

Mirror

Angle of incidence

Angle of reflection

Diagram 1

(b) James set up a different experiment as shown below:

He measured the angle of refection for different angles of incidence.

His results are shown in the graph.

Use the graph to answer the questions below:

When the angle of refraction is 20⁰, what is the angle of incidence?

................................⁰ 1 mark

What conclusion could James draw from his graph?

When light passes from air into glass, the angle of incidence is always ....................

the angle of refraction. 1 mark

On diagram 2, draw a line to continue the refracted ray as it leaves the glass block. 1

mark.

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70

An

gle

of

refr

acti

on

Angle of incidence

Diagram 2

Glass block

Angle of incidence

Angle of refraction

Refracted ray

Incident ray

Electromagnetic spectrum

https://www.tutorialspoint.com/The-Electromagnetic-Spectrum

https://www.bbc.co.uk/bitesize/guides/zd2ddxs/revision/2

https://www.mathsisfun.com/physics/waves-radio-microwave.html

Complete the table in as much detail as possible.

Region of EM spectrum

Frequency range (Hz)

Source Uses in communication

Radio waves

Microwaves

Infra-red radiation

Visible light

BTEC Applied Science Physics

Practice questions

1. Waves may be either longitudinal or transverse.

(a) Describe the difference between a longitudinal and a transverse wave.

___________________________________________________________

___________________________________________________________

___________________________________________________________

________________________________________________________ (2)

(b) Describe one piece of evidence that shows when a sound wave travels through the air it is the wave and not the air itself that travels.

___________________________________________________________

___________________________________________________________

___________________________________________________________

(1)

2. Different parts of the electromagnetic spectrum are useful for different methods of

communication.

The diagram shows a transmitter emitting two electromagnetic waves, L and M.

(a) (i) Wave L is used to send a signal to a satellite. Which part of the electromagnetic spectrum does wave L belong to?

____________________________________________________ (1)

(ii) What name is given to the process that occurs as wave L passes into the ionosphere?

___________________________________________________ (1)

(b) Wave M is reflected by the ionosphere.

(i) On the diagram above, draw the path of wave M until it reaches the receiver.

(2)

(ii) On the diagram above, draw a line to show the normal where wave M meets the ionosphere. Label the line N.

(1)

(c) Give two properties of all electromagnetic waves.

1. ________________________________________________________

___________________________________________________________

2. _________________________________________________________

_________________________________________________________ (2)

(Total 7 marks)

3. (a) Electromagnetic waves form a continuous spectrum with a range of

wavelengths.

What is the approximate range of wavelengths of electromagnetic waves? Tick ( ) one box. (1)

10–15 metres to 104 metres

10–4 metres to 1015 metres

10–6 metres to 106 metres

(b) Infrared waves and microwaves are used for communications.

(i) Give one example of infrared waves being used for communication.

___________________________________________________ (1)

(ii) A mobile phone network uses microwaves to transmit signals through the air. The microwaves have a frequency of 1.8 × 109 Hz and travel at a speed of 3.0 × 108 m/s.

Calculate the wavelength of the microwaves. Give your answer to two significant figures.

_______________________________________________________

Wavelength = ___________________________ m (3)

(c) Some scientists suggest there is a possible link between using a mobile phone and male fertility.

The results of their study are given in the table.

Mobile phone use in hours per day

Sperm count in millions of sperm cells per cm3 of

semen

0 86

less than 2 69

2 – 4 59

more than 4 50

The results show a negative correlation: the more hours a mobile phone is used each day, the lower the sperm count. However, the results do not necessarily mean using a mobile phone causes the reduced sperm count.

Suggest one reason why.

___________________________________________________________

_________________________________________________________ (1)

(Total 6 marks)

4. All radio waves travel at 300 000 000 m/s in air.

(i) Give the equation that links the frequency, speed and wavelength of a wave.

_________________________________________________________ (1)

(ii) Calculate the wavelength, in metres, of a radio wave which is broadcast at a frequency of 909 kHz. Show clearly how you work out your answer.

___________________________________________________________

___________________________________________________________

___________________________________________________________

Wavelength = ________________ metres

(2)

(Total 3 marks)

5. (a) Microwaves are one type of electromagnetic wave.

(i) Which type of electromagnetic wave has a lower frequency than microwaves?

____________________________________________________ (1)

(ii) What do all types of electromagnetic wave transfer from one place to another?

___________________________________________________ (1)

(b) The picture shows a tennis coach using a speed gun to measure how fast the player serves the ball.

(i) The microwaves transmitted by the speed gun have a frequency of 24 000 000 000 Hz and travel through the air at 300 000 000 m/s.

Calculate the wavelength of the microwaves emitted from the speed gun.

Show clearly how you work out your answer.

_____________________________________________________

_______________________________________________________

Wavelength = _______________ m

(2)

(ii) Some of the microwaves transmitted by the speed gun are absorbed by the ball.

What effect will the absorbed microwaves have on the ball?

_______________________________________________________

_______________________________________________________

(1)

(Total 5 marks)

6. (a) Microwaves and visible light are two types of electromagnetic wave. Both can

be used for communications.

(i) Give two properties that are common to both visible light and microwaves.

1. ____________________________________________________

_______________________________________________________

2. ____________________________________________________

____________________________________________________ (2)

(ii) Name two more types of electromagnetic wave that can be used for communications.

___________________________ and __________________ (1)

(b) Wi-Fi is a system that joins computers to the internet without using wires. Microwaves, with a wavelength of 12.5 cm, are used to link a computer to a device called a router. Microwaves travel through the air at 300 000 000 m/s.

Calculate the frequency of the microwaves used to link the computer to the router.

Show clearly how you work out your answer and give the unit.

___________________________________________________________

___________________________________________________________

Frequency = _______________________________

(3)

(c) Wi-Fi is used widely in schools. However, not everyone thinks that this is a good idea.

A politician commented on the increasing use of Wi-Fi. He said: ‘I believe that these systems may be harmful to children.’

However, one group of scientists said that there is no reason why Wi-Fi should not be used in schools. These scientists also suggested that there is a need for further research.

(i) Suggest what the politician could have done to persuade people that what he said was not just an opinion.

___________________________________________________(1)

(ii) Why did the group of scientists suggest that there is a need for further research?

_________________________________________________ (1)

7. Radio waves and microwaves are two types of electromagnetic wave.

Both waves:

• can be used for communications

• travel at the same speed through air.

(a) Give two more properties that are the same for both radio waves and microwaves.

1. ________________________________________________________

___________________________________________________________

2. ________________________________________________________

________________________________________________________ (2)

(b) Some satellites are used to transmit television programmes. Signals are sent to, and transmitted from, the satellites using microwaves.

What is the property of microwaves that allows them to be used for satellite communications?

___________________________________________________________

_________________________________________________________ (1)

(c) Electromagnetic waves travel at a speed of 3.0 × 108 m/s.

A radio station transmits waves with a wavelength of 2.5 × 102 m.

Calculate the frequency of the radio waves.

Show clearly how you work out your answer and give the unit.

___________________________________________________________

___________________________________________________________

___________________________________________________________

Frequency = ___________________________________

(3)

(Total 6 marks)

8. (a) The wavelengths of four different types of electromagnetic wave, including

visible light waves, are given in the table.

Type of wave Wavelength

Visible light 0.0005 mm

A 1.1 km

B 100 mm

C 0.18 mm

Which of the waves, A, B, or C, is an infra red wave?

________________________________________________________ (1)

(b) A TV station broadcasts at 500 000 kHz. The waves travel through the air at 300 000 000 m/s.

Calculate the wavelength of the waves broadcast by this station.

Show clearly how you work out your answer.

___________________________________________________________

___________________________________________________________

Wavelength = ________________________ m

(2)

(c) What happens when a metal aerial absorbs radio waves?

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

(2)

(d) Stars emit all types of electromagnetic waves. Telescopes that monitor X-rays are mounted on satellites in space.

Why would an X-ray telescope based on Earth not be able to detect X-rays emitted from distant stars?

___________________________________________________________

_________________________________________________________

(1)

(Total 6 marks)

9. Some students made a small hand-turned a.c. generator, similar to a bicycle

dynamo. They connected it to the Y plates of a cathode ray oscilloscope, CRO, and turned the generator slowly. The trace on the CRO looked like this:

They then turned the generator faster and the trace looked like this:

(a) Why did the trace on the CRO show:

(i) an increase in frequency;

____________________________________________________ (1)

(ii) a decrease in wavelength;

____________________________________________________ (1)

(iii) an increase in amplitude?

____________________________________________________ (1)

(b) One way to alter the output from the generator is to change the speed of turning. State two other ways to adapt parts of the generator to increase its output.

___________________________________________________________

_________________________________________________________ (2)

(Total 5 marks

BTEC Applied Science Physics

Challenge questions

1. The graph shows how the vertical height of a travelling wave varies with distance

along the path of the wave.

The speed of the wave is 20 cm s–1. What is the period of the wave?

A 0.1 s

B 0.2 s

C 5.0 s

D 10.0 s

(Total 1 mark)

2. (a) Distinguish between longitudinal and transverse waves.

___________________________________________________________

___________________________________________________________

___________________________________________________________

_______________________________________________________ (2)

3 (a) Explain what is meant by a progressive wave.

___________________________________________________________

________________________________________________________ (2)

(b) Figure 1 shows the variation with time of the displacement of one point in a progressive wave.

Figure 2 shows the variation of displacement of the same wave with distance.

Use Figures 1 and 2 to determine

(i) the amplitude of the wave amplitude = ___________ mm

(1)

(ii) the wavelength of the wave wavelength = _____________ m

(1)

(iii) the frequency of the wave frequency = _____________ Hz

(1)

(iv) the speed of the wave speed = _____________ m s−1 (1)

4. The figure below shows two ways in which a wave can travel along a slinky spring.

(a) State and explain which wave is longitudinal.

___________________________________________________________

___________________________________________________________

(2)

(b) On the figure above,

(i) clearly indicate and label the wavelength of wave B

(1)

(ii) use arrows to show the direction in which the points P and Q are about to move as each wave moves to the right.

(2)

(c) Electromagnetic waves are similar in nature to wave A.

Explain why it is important to correctly align the aerial of a TV in order to receive the strongest signal.

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

(2)

(Total 7 marks)

5. The figure below shows a continuous progressive wave on a rope. There is a knot in

the rope.

(a) Define the amplitude of a wave.

___________________________________________________________

_________________________________________________________ (2)

(b) The wave travels to the right. Describe how the vertical displacement of the knot varies over the next complete cycle.

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

________________________________________________________ (3)

(c) A continuous wave of the same amplitude and frequency moves along the rope from the right and passes through the first wave. The knot becomes motionless. Explain how this could happen.

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

(3)

(Total 8 marks)

6. Ultrasound waves are used to produce images of a foetus inside a womb.

(a) Explain what is meant by the frequency of a wave.

___________________________________________________________

________________________________________________________ (1)

(b) Ultrasound is a longitudinal wave. Describe the nature of a longitudinal wave.

___________________________________________________________

_________________________________________________________ (2)

(c) In order to produce an image with sufficient detail, the wavelength of the ultrasound must be 0.50 mm. The speed of the ultrasound in body tissue is 1540 m s–1. Calculate the frequency of the ultrasound at this wavelength. Give your answer to an appropriate number of significant figures.

frequency ____________________ Hz (2)

(d) A continuous ultrasound wave of constant frequency is reflected from a solid surface and returns in the direction it came from.

Assuming there is no significant loss in amplitude upon reflection, describe and explain the effect the waves have on the particles in the medium between the transmitter and the solid surface.

___________________________________________________________

___________________________________________________________

___________________________________________________________

______________________________________________________ (3)