P1.5.1 General Properties of waves Mr D Powell Mr Powell 2012 Index Connection Connect your learning to the content of the lesson Share the process by.

P1.5.1 General Properties of waves

P1 PHYSICSMr D Powell

Mr Powell 2012Index

Connection

• Connect your learning to the content of the lesson

• Share the process by which the learning will actually take place

• Explore the outcomes of the learning, emphasising why this will be beneficial for the learner

Demonstration

• Use formative feedback – Assessment for Learning

• Vary the groupings within the classroom for the purpose of learning – individual; pair; group/team; friendship; teacher selected; single sex; mixed sex

• Offer different ways for the students to demonstrate their understanding

• Allow the students to “show off” their learning

Activation

• Construct problem-solving challenges for the students

• Use a multi-sensory approach – VAK• Promote a language of learning to

enable the students to talk about their progress or obstacles to it

• Learning as an active process, so the students aren’t passive receptors

Consolidation

• Structure active reflection on the lesson content and the process of learning

• Seek transfer between “subjects”• Review the learning from this lesson and

preview the learning for the next• Promote ways in which the students will

remember• A “news broadcast” approach to learning

Mr Powell 2012Index

P1.5.1 General Properties of waves (Part A)

a) Waves transfer energy.

b) Waves may be either transverse or longitudinal. (transverse wave the oscillations are perpendicular to the direction of energy transfer. In a longitudinal wave the oscillations are parallel to the direction of energy transfer.)

c) Electromagnetic waves are transverse, sound waves are longitudinal and mechanical waves may be either transverse or longitudinal.

d) All types of electromagnetic waves travel at the same speed through a vacuum (space).

e) Electromagnetic waves form a continuous spectrum. (should know the order of electromagnetic waves within the spectrum, in terms of energy, frequency and wavelength and appreciate that the wavelengths vary from about 10 –15 metres to more than 104 metres.)

f) Longitudinal waves show areas of compression and rarefaction.

Mr Powell 2012Index

P1.5.1 The Nature of Waves... P78-79

a) Waves transfer energy. (Basic)

b) Waves may be either transverse or longitudinal. (transverse wave the oscillations are perpendicular to the direction of energy transfer. In a longitudinal wave the oscillations are parallel to the direction of energy transfer.) (Basic)

c) Electromagnetic waves are transverse, sound waves are longitudinal and mechanical waves may be either transverse or longitudinal. (Basic)

d) All types of electromagnetic waves travel at the same speed through a vacuum (space). (Basic)

f) Longitudinal waves show areas of compression and rarefaction. (Harder)

P1.5.1

Mr Powell 2012Index

Energy Delivery...

A key idea for an wave is that the shorter the wavelength or higher the frequency the more energy is delivered per second to an object.

It makes sense that for a wave which travels at the same speed 300,000,000m/s (in a vacuum) is it is shorter then more will arrive per second each delivering energy.

P1.5.1

Mr Powell 2012Index

Energy Delivery...

A good analogy is a water wave arriving on a beach.

Energy arrives as the peak of each wave arrives

More peaks per second means more energy per second

More J/s is more Power or Watts.

Example you sit in the sun and get hotter the longer you sit there.

The more waves arrive the thermal energy is deposited on your skin

P1.5.1

Mr Powell 2012Index

Longitudinal Waves

Using a slinky you can try this out.

In fact we are modelling how the air molecules compress and expand when we talk.

Rarefaction is an expansion!

Try it with a slinky!

VIBRATION

• Common examples:- Sound, slinky springs seismic p waves

• Longitudinal waves cannot be polarisedP1.5.1

Mr Powell 2012Index

Longitudinal

11

• The direction of vibration of the particles is parallel to the direction in which the wave travels.

• Common examples:- Sound, slinky springs seismic p waves

• Longitudinal waves cannot be polarised

Direction of travel

VIBRATION

P1.5.1

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Transverse

12

• The direction of vibration of the particles is perpendicular to the direction in which the wave travels.

• Common examples:- Water, electromagnetic, ropes, seismic s waves

• You can prove that you have a transverse wave if you can polarise the wave (especially important with light (electromagnetic) as you cannot “see” the wave!!)

Direction of travel

vibration

Try it with a slinky!P1.5.1

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Exam Question…. (Basic Level)

(a) State the characteristic features of

(i) longitudinal waves,........................................................................................................................................................................................................................................................

(ii) transverse waves.........................................................................................................................................................................................................................................................

(3)

Answera)

(i) particle vibration (or disturbance or oscillation) (1)same as (or parallel to) direction of propagation (or energy transfer) (1)

(ii) (particle vibration)perpendicular to direction of propagation (or energy transfer) (1)

P1.5.1

Mr Powell 2012Index

The speed of electromagnetic radiation in a vacuum is 299,792,458 m/s.

Which is often quoted as 300,000km/s or 3 x 108km/s

This is approximately three hundred million metres per second - nearly nine hundred thousand times faster than sound, which is why you see a flash of lightning before you hear the thunder.

All EM waves travel through space (which is empty of matter) at the speed of light. Light is an example of an EM wave.

If the EM wave enters a medium such as air it will slow down, then a prism even more.

P1.5.1

d) All types of electromagnetic waves travel at the same speed through a vacuum (space). (Basic)

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P1.5.1 The Nature of Waves... P78-79 “Quick Test”....

1. Name the two main types of mechanical waves (2 marks)

2. Give an example of each type of wave (2 marks)

3. Explain a feature of each type of wave (2 marks)

4. What is the value of the speed of light (1 mark)

5. Draw a diagram to show the main features of (3 marks)

Basic Demand

Med Demand

High Demand

Student Assessed!

? / 10

Mr Powell 2012Index

P1.6.1 The Electromagnetic Spectrum p94 (only first section)

e) Electromagnetic waves form a continuous spectrum. (BASIC)

Know the order of electromagnetic waves within the spectrum in terms of:

1. Energy2. Frequency3. Wavelength (Medium)

Appreciate that the wavelengths vary from about 10–15 metres to more than 104 metres. (Harder)

P1.6.1 p94-96

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This is the EM Spectrum... SCan you remember any parts of it. Write out 1-8 in your books and test yourself?

1 2 3 4 5 6 7 8

P1.6.1 p94-96

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The EM Spectrum

This is the Electromagnetic Spectrum. It is a range of waveforms which deliver energy from one place to another with different frequencies and wavelengths.

T

Longer wavelength

Higher Frequency

P1.6.1 p94-96

Mr Powell 2012Index

Spectrum Summary

Wave Wavelength Use

Long Wave Radio 1500 m BroadcastingMedium Wave Radio 300 m Broadcasting

Short Wave Radio 25 m Broadcasting

FM Radio 3 m Broadcasting and communication

UHF Radio 30 cm TV transmissions

Microwaves 3 cmCommunication

RadarHeating up food

Infra red 3 mmCommunication in optical fibres

Remote ControllersHeating

Light 200 - 700 nm SeeingCommunicating

Ultra violet 100 nm SterilisingSun tanning

X-ray 5 nm Shadow pictures of bones

Gamma rays <0.01 nm Scientific research

P1.6.1 p94

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Hazards of EM Radiation...

Wave Wavelength Hazard Prevention

Long Wave Radio 1500 m No hazard

Medium Wave Radio 300 m No hazard

Short Wave Radio 25 m No hazard

FM Radio 3 m No hazard UHF Radio 30 cm No hazard

Microwaves 3 cm Heating of water in the body Metal grid

Infra red 3 mm Heating effect Reflective surface

Light 200 - 600 nm No hazard

Ultra violet 100 nm Can cause cancer Sun cream (or cover up)

X-ray 5 nm Causes cell damage Lead screens

Gamma rays <0.01 nm Causes cell damage Thick lead screens or concrete

P1.6.1 p94P1.6.1 p94-96

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Which word links all of these images... S

P1.6.1 p94-96

Visible Light

White light is dispersed by a prism to form a spectrum (not to scale)

Wavelength in nanometres (nm)1x10-9 or x 0.000000001m

Visible light is detected by the human eye. White light consists of ROY-G-BIV (as shown above). Each colour is a range of wavelengths and is absorbed differently by the cells in the eye.

Visible light is the middle part of the EM Spectrum sandwiched between Ultraviolet (more than violet) & Infra Red (less than red)

Violet 433 - 400

Indigo 466 - 432

Blue 500 - 465

Green 570 - 599

Yellow 590 - 569

Orange 610 - 589

Red 750 - 609

Copy text & diagram

Mr Powell 2012Index

Visible Light

O Y V

Infra Red Ultraviolet

>750 750 -609 610-589 500-465 466-432 433-400 <400


Shorter Wavelength

Higher Frequency

Copy & Complete

P1.6.1 p94-96

Mr Powell 2012Index

Visible Light

IR R O Y G B I V UV

Infra Red Red Orange Yellow green Blue Indigo Violet Ultraviolet

>750 750 -609 610-589 590-569 570-500 500-465 466-432 433-400 <400


Shorter Wavelength

Higher Frequency

Answers

P1.6.1 p94-96

P1.6.1 p94-96

Y V

Infra Red

>750 750 -609 500-465 433-400

Y V

Infra Red

>750 750 -609 500-465 433-400

Y V

Infra Red

>750 750 -609 500-465 433-400

P1.5.1 General Prop of waves (Part A)





















Mr Powell 2012Index

P1.5.1 General Properties of waves (Part B)g) Waves can be reflected, refracted and diffracted. (significant diffraction only occurs when the wavelength of the wave is of the same order of magnitude as the size of the gap or obstacle.)

h) Waves undergo a change of direction when they are refracted at an interface.

i) The terms frequency, wavelength and amplitude.

j) All waves obey the wave equation:v = f

v is speed in metres per second, m/sf is frequency in hertz, Hz is wavelength in metres, m

k) Radio waves, microwaves, infrared and visible light can be used for communication.

Should be familiar with situations in which such waves are typically used andany associated hazards, eg:

1. radio waves – television, and radio (including

2. diffraction effects)3. microwaves – mobile

phones and satellite television

4. infrared – remote controls

5. visible light – photography.

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P1.6.1 The Electromagnetic Spectrum (next part! P94)

j) All waves obey the wave equation:

v = f ( or c = f)

v is speed in metres per second, m/sf is frequency in hertz, Hz is wavelength in metres, m

P1.5.2 p80 / P1.6.1 p94

e) Electromagnetic waves form a continuous spectrum. (BASIC)

Know the order of electromagnetic waves within the spectrum in terms of: Energy, Frequency, Wavelength (Medium)

Appreciate that the wavelengths vary from about 10–15 metres to more than 104 metres. (Harder)

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Practical Investigation...

1. Take your ruler and investigate the sound wave it creates by “twanging” it with your fingers. (Take care not to break it)

2. Think about the relationship between pitch (frequency) and length.

3. Then make a verbal prediction for what might happen with a string or tube?

Mr Powell 2012Index

What is a wave?

Waves can be produced in ropes, springs and on the surface of water.

When waves travel along ropes or springs or across the surface of water they set up regular patterns of disturbance. They are a way of transferring energy from one point to another without transferring matter.

The maximum disturbance caused by a wave is called its amplitude

The distance between a particular point on one disturbance and the same point on the next is called the wavelength

The number of waves each second produced by a source (or passing a

particular point) is called the frequency, and is measured in hertz (Hz).

We can find the speed of a wave from the formula;

wave speed = frequency x wavelength

fvP1.5.2 p80 / P1.6.1 p94

Mr Powell 2012Index

Using the Formula

This waveform has a wavelength of 3m. By inspection it takes 2 seconds for a complete cycle (1 up & 1 down)

To work out the frequency then wave speed we must find out how many cycles there are in one second;

3m

15.1

/5.1

35.0

msv

smv

mHzv

fv

Hzf

sf

sf

cycleafortimef

5.0

5.0

2

1

1

1

fv

f

v

fv

P1.5.2 p80 / P1.6.1 p94

Mr Powell 2012Index

The photograph shows waves travelling across the surface of a pond.

1m

Is this an example of a transverse or longitudinal wave?

Estimate the wavelength of the wave:

If the frequency of the wave is 0.2 Hz, calculate the speed of the wave:

transverse

0.15m

0.03m/s

Question....

P1.5.2 p80 / P1.6.1 p94

Mr Powell 2012Index

Wave WavesTime (s)

Frequency(Hz)

2

2

2

Wave Equation

If three waveforms are monitored over a time of 2 seconds can you fill in the table?

6

10

1

3

5

0.5

P1.5.2 p80 / P1.6.1 p94

Mr Powell 2012Index

Plenary Questions..

1. Work out the frequency of a wave which travels at a speed of 666ms-1 and has a wavelength of 3m?

2. What is the speed of a wave which has a frequency of 125Hz, and wavelength of 0.03m?

3. What is the speed of a wave which has a frequency of 2000Hz, and wavelength of 73m?

4. What is the wavelength of a wave travelling at 10,000 ms-1 if its frequency is 25MHz?

5. What is the speed of a wave with wavelength of 0.000001m and frequency 1 MHz?

fv

1. 222Hz2. 3.75m3. 146kHz4. 0.0004m5. 1Hz

P1.5.2 p80 / P1.6.1 p94

Mr Powell 2012Index

P1.6.1 The Electromagnetic Spectrum p94 (only first section)“Quick Test”....

1. Give the main order of the EM spectrum (3 marks)

2. Make it clear which part of the spectrum has low-high freq or wavelength (1 mark)

3. Which part of the spectrum is more dangerous and why (2 marks)

4. If a wave travels as 3 x 108ms-1 and has a wavelength of 900 million Hz what would it’s wavelength be? (2 marks)

Basic Demand

Med Demand

High Demand

Student Assessed!

? / 8

f

c

fc

Mr Powell 2012Index

Wave Properties: P1.5.3 Reflection/ 1.5.4 Refraction/ 1.5.5Diffraction p82-87

g) Waves can be reflected, refracted and diffracted.

h) Waves undergo a change of direction when they are refracted at an interface. – video!

(significant diffraction only occurs when the wavelength of the wave is of the same order of magnitude as the size of the gap or obstacle)

Explain law of reflection & a diagram of basic reflection (Basic)Explain/ draw a “virtual” image diagram (Harder)

Explain the idea of refraction using a glass prism (Basic)Explain dispersion using a triangular prism (Medium)Explain refraction using a water tank and depth change (Harder)

Explain how diffraction changes depending on gap size (Basic)Explain how diffraction used in ultra sound (Medium)Explain how microwaves can show diffraction (Harder)

P1.5.3/1.5.4/1.5.5 p-82-87

Mr Powell 2012Index

Reflection.... p82

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Refraction.... p84

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Refraction.... “Spectrums” “Dispersion”

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Diffraction... p86

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Diffraction... P86 - Radio?

This explains why it is possible to hear sounds and receive radio signals even if there is something between you and the source of the waves.

If the wavelength of the waves is shorter the spreading, diffraction, effect is much smaller as well.

This explains why television waves (shorter) are much more difficult to receive in hilly areas than radio waves which have a longer wavelength and why the diffraction of light (very short) is so difficult to observe.

Mr Powell 2012Index

Key Points

Refraction….

Waves pass a boundary i.e. air to glass prism or deep to shallow water they “refract” or change direction and change speed. Light bends in towards the normal for air to glass and reverse as it comes out. Water waves moving into the shallows slow down and have smaller . c= f so if c so

Diffraction….

Wave fronts incident on a gap. The narrower the gap the more the waves curve or the longer/larger the wavelength the more they spread out.

P1.5.3/1.5.4/1.5.5 p-82-87

TASK: Watch the videos and look at P1.5.4 p84/ P1.5.5 p86 to help you understand the idea of refraction and diffraction.

1. Make a set of summary notes for each topic of the key points.

2. Now move onto some practical investigations to assist in your understanding.

Mr Powell 2012Index

HW: Virtual Ripple Tanks…

Use the virtual ripple tank here to explore wave properties.

http://www.falstad.com/ripple/

Make summary notes on what you find for a variety of situations.

You may decide to screenshot out the image to help you. (NB: pick a nice colour scheme)

P1.5.3/1.5.4/1.5.5 p-82-87

http://www.falstad.com/ripple/

Mr Powell 2012Index

Wave Properties: P1.5.3 Reflection/ 1.5.4 Refraction/ 1.5.5 Diffraction

1. Light is incident on a mirrored surface at 30 what is the angle of reflection (1 mark)

2. Light is incident on a glass prism at an angle of 30 what happens to the ray inside the prism? (2 marks)

3. Water waves are incident on a small gap approx the size of the wavelength () what happens? (2 marks)

4. Sometimes at certain angles you can see an object behind a mirror what is this called? (1 mark)

5. When white light is incident of a triangular prism it produces a spectrum of light (dispersion). Why is this? (1 mark)

6. When water waves reach a shallower part what happens to the speed and wavelength? (2 marks)

7. If you make the gap in question 3 larger what happens to the pattern? (1 mark)

Basic Demand

Med Demand

High Demand

Student Assessed!

? / 10

Mr Powell 2012Index

EM Spectrum Revision.... S

Mr Powell 2012Index

P1 6.2 Light, IR, Microwaves & Radio & P1.6.3 Communications.


Give examples of how light, IR, Microwaves & Radio can be used to transfer data.

• Draw an example with a diagram (Basic)

• Label the diagram to explain it (Medium)

• Explain key properties of the waves used i.e. Frequencies or wavelengths and how the mediums they travel through change the waves (Harder)

• Give examples of Radio and TV and how they move through the atmosphere (Medium)

• Use context of the British Army to explain how they use EM Waves (from slides) (Harder)

P1.6.2 p96 / P1.6.2 p98

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TASK

Look at the summary of the role of of the Royal Signals.

Can you present and summarise the key points of text into bullet point form in your book.

Royal Signals Case Study.... MAs the IT and Communications providers for the British Army the Royal Signals Corps deploy everywhere the Army goes.

Its role is to provide the Command, Control and Information systems that are required to enable the rest of the Army to communicate - in essence, the equivalent of BT or a mobile telephone provider, but within in an operational environment where there may not be any other form of communications available. From small tactical radio communications equipment to large satellite dishes linking continents and passing vast amounts of information - the Royal Signals delivers communication solutions using some of the most advanced technology in the world today. The ingenuity, creativity and expertise of the Royal Signals are renowned often having to adapt equipment for extreme climatic and geographical conditions. Providing digital, VHF and satellite communications anywhere in the world, the RSC provides fully secure communications in all environments and conditions.

D-E

P1.6.2 p96 / P1.6.2 p98

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SystemsPtarmigan is the current mainstay of the Army's Tactical Trunk Communications System and provides fullysecure digital communications throughout the battlefield.

Clansman is the in-service family of tactical radios with which the British Army is currently equipped to provide communications from formation headquarters to the fighting units.

Bowman is the new tactical communications system. It will exploit the latest developments in radio andcomputer technology to meet the needs for all three services well into the 21st century. This will for the first time give commanders at all levels secure voice and data communications as well as an integrated Global Positioning System (GPS). The Army uses tactical satellite ground terminals (SGT) which can provide high quality, high bandwidth communications links at very short notice anywhere in the world.

TASK

Read about the current systems available to the UK Army in Helmand Province Afghanistan.

Can you Prioritise and Summarise what you think are the main features of an Army coms system that is essential and fit for purpose? (this develops on from the previous idea.)

B/C

P1.6.2 p96 / P1.6.2 p98

Mr Powell 2012Index

Microwaves Case Study...

Microwave oven:

They are absorbed by water and food contains water and this effect causes food to heat by vibrating its molecules. The fact that metal reflects microwaves allows us to contain them within the oven.

Satellites:

They can pass freely through the atmosphere and ionosphere, allowing them to go into space and to come back to earth. The electromagnetic radiation within a microwave is able to carry a signal which can then be converted into information on its arrival at a receiver.

P1.6.2 p96 / P1.6.2 p98

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Radio waves M You might wonder how we manage to listen to the radio and watch television and receive long distance signals.

This diagram shows that we can in fact bounce longer wavelength signals off the ionosphere (a layer in the atmosphere). This layer changes with the seasons. (stronger – summer)

TASKSSketch out the

diagram and label how we get our signals and why?

D-E

radio

TV

P1.6.2 p96 / P1.6.2 p98

Mr Powell 2012Index

Examples of Communications Waveforms.

Medium Frequency used in older military radios

Very High Frequency (VHF) or Ultra High Frequency (UHF) used by commercial radio or TV bands

Extremely Low Frequency (ELF) used by submarines

P1.6.2 p96 / P1.6.2 p98

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Complex View I - extension

The ionosphere is the uppermost part of the atmosphere, distinguished because it is ionised by solar radiation.

It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere.

It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.

P1.6.2 p96 / P1.6.2 p98

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Complex View II - extensionThe ionosphere is broken down into the D, E and F regions. The breakdown is based on what wavelength of solar radiation is absorbed in that region most frequently.

The D region is the lowest in altitude, though it absorbs the most energetic radiation, hard x-rays. The D region doesn't have a definite starting and stopping point, but includes the ionization that occurs below about 90km.

The E region peaks at about 105km. It absorbs soft x-rays.

The F region starts around 105km and has a maximum around 600km. It is the highest of all of the regions. Extreme ultra-violet radiation (EUV) is absorbed there.

On a more practical note, the D and E regions reflect AM radio waves back to Earth. Radio waves with shorter lengths are reflected by the F region. Visible light, television and FM wavelengths are all too short to be reflected by the ionosphere. So your t.v. stations are made possible by satellite transmissions or direct air to air on Earth transmission

P1.6.2 p96 / P1.6.2 p98

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IR Light

1. Infra red waves are absorbed by air, but are readily transmitted by glass.

2. Visible light is rapidly absorbed by glass.

3. Therefore infra-red is used for telecommunication by optical fibres.

4. Optical fibres are very flexible and allow the infra red signals to travel around corners.

P1.6.2 p96 / P1.6.2 p98

Mr Powell 2012Index

Microwaves Properties

They can pass through the atmosphere and the ionosphere

They can pass through glass and plastic

They are reflected by metal

They are absorbed by water molecules

They can cause materials to heat by vibrating their molecules

They travel at the speed of light or 300,000,000 m/s

They are transverse waves.

P1.6.2 p96 / P1.6.2 p98

http://en.wikipedia.org/wiki/Microwave_oven



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Penetration of Microwaves

P1.6.2 p96 / P1.6.2 p98

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Microwaves Extension... G&TWater molecules are dipolar molecules. This means that they organise their electrons in such a way as to make one side of the molecules positively charged and the other side negatively charged.

Microwaves are actually radio waves in a specific wavelength and frequency band. In microwave ovens this is usually around 12.2 cm and 2.45 GHz. Microwaves (and all other electromagnetic waves) form oscillating electric fields which go from positive to negative and back again in this case 2.45 billion times a second.

Because opposite charges attract and like charges repel and the electric field keeps changing from positive to negative and back again, this forces the water molecules to continuously realign themselves to try and keep up.

This rotational motion causes the molecules to bump into each other increasing their random (movement or) kinetic energy. The random kinetic energy of molecules is another way of describing heat! So the more kinetic energy the molecules have the hotter the material becomes.

TASK

Read about the information about how microwaves heat water.

Now try to explain the situation using your own labelled diagram created from the text.

Draw spiders out with detailed explanations…

A*-B

Mr Powell 2012Index

P1 6.2 Light, IR, Microwaves & Radio & P1.6.3 Communications.

1. Name the visible spectrum of light (3 marks)2. Where does IR radiation lie compared to visible (1 mark)3. Where does UV radiation lie compared to visible (1 mark)

4. Give a two example(s) of the use of IR radiation (1 mark)5. Give a two example(s) of the use of microwave radiation

other than cooking (1 mark)

6. Explain how radio can be used for PC peripheral communications? (2 marks)

7. Why are microwaves dangerous at higher powers (1 mark)

Basic Demand

Med Demand

High Demand

Student Assessed!

? / 10

Mr Powell 2012Index

Extra Questions....

receiver a.c

ariel

Transmitterfrequency

interference obstructions

frequency

heard seen receiver

pictures sound

Alternating currents, ariel, transmitter, frequency

heard, seen, receiver, sound, pictures

Interference, frequency, obstructions

P1.6.2 p96 / P1.6.2 p98

P1.5.1 General Prop of waves (Part B)

g) Waves can be reflected, refracted and diffracted. (significant diffraction only occurs when the wavelength of the wave is of the same order of magnitude as the size of the gap or obstacle.)




v = f v is speed in metres per second, m/sf is frequency in hertz, Hz is wavelength in metres, m
















P1.5.1 General Properties of waves Mr D Powell Mr Powell 2012 Index Connection Connect your learning to the content of the lesson Share the process by.

Documents

waves transfer energy

sound waves

mechanical waves

nature of waves

basic f longitudinal

e electromagnetic waves

order of electromagnetic

learning slide