Section 4 Waves

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Section 3: Waves

a) Units

b) Properties of waves

c) The electromagnetic spectrum

d) Light and sound

a) Units3.1 use the following units: degree (o), herts (!), "eter ("), "eter#second ("#s), second (s).

S.

NoQuantity unit

Symb

ol

1

Frequency

Definition:

Number of vibrations in a second.

OR

number of ccles in a second

OR

Total number of waves passing through a single point!mar" in a

second.

#ert$

or

%cles!sec

ond

#$

&

Wavelength

Definition: distance between two consecutive crest or trough.

'eter

m


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S.

NoQuantity unit

Symb

ol

( peed of waves'eter!seco

ndm!s

continue on ne*t page

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S.N

oQuantity unit Symbol

+

Amplitude

Definition:

'a*imum displacement of particle!atom!molecule or an

ob,ect from mean position.

'eter m


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S.N

oQuantity unit Symbol

-

Time period or Period

Definition:

Time ta"en to complete one vibration.

/

Time ta"en for a wave to pass through a single point.

The definition of time period and fre0uenc loo" similar

because the are inversel related to each other.

f 1!T or T 1!f

Note: 2t is discussed in section (.(

econd s

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%eneral Wave Pro&erties(a) descri'e what is "eant ' wave "otion as illustrated ' vi'rations in ro&es and s&rings and ' e&eri"entsusing a ri&&le tan*.

3hat is a wave4

The motion of ropes and springs and e*periments b ripple tan" shows that energ is trasported from one place to another while

matter is onl temporaril disturbed.

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(') state what is "eant ' the ter" wavefront.

5 wave is graphicall represented b sine or cosine curve as shown below


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2f we draw vertical lines through each crest then these lines are called wavefront as shown below

The wavefronts are then straight parallel lines as shown below

3avefronts are easier wa of representing waves than sine and cosine curve.

The distance between two consecutive wavefronts is called one wavelength.

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(c) define the ter"s s&eed, freuenc, wavelength and a"&litude and do calculations using velocit -freuenc wavelength.


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Definitions are given in chart shown above.

Definitions are given in section (.1. 6raphical representation as shown below.

5mplitude of the waves contains energ. #igher the amplitude higher the amount of energ that waves contains.

Learn following e0uation b heart.

wave speed fre0uenc 7 wavelength

v f 7 8

Learn following e0uation b heart.

wave speed fre0uenc 7 wavelength

v f 7 8

9 %alculate the fre0uenc of the wave having wavelenght 1 * 1;


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There are two types of waves i- longitudinal waves ii- trasnverse waves

Longitudinal Wave:

Such a wave motion in which particles vibrate parallel to the direction of wave motion.

As you can see in the video, disturbance is occuring in the same direction as the lenght of the spring--both horizontal.

http:www.youtube.comwatch!v"agu#Wnb$%T&

'ongitudinal wave has two ma(or parts

i) #ompression: where particles *atoms or molecules) are compressed, it+s a high pressure region.

ii) $arefaction: Where particles *atoms or molecules in real situations) are epanded. t is an epansion region where pressure

is low.

The distance between two consecutive compressions or rarefactions is called wavelength of the longitudinal wave.
http://www.youtube.com/watch?v=aguCWnbRETUhttp://www.youtube.com/watch?v=aguCWnbRETU


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The movement of longitudinal wave can be seen as the movement of compression and rarefaction.

%amples of 'ongitudinal waves: Sound waves, Seismic -waves / wave in spring are some naturally occuring waves.

Transverse waves: Such a wave in which particles disturbedvibrate perpendicular to the direction of wave motion.

#ommon eample water wave, light waves, waves in ropes, stadium waves and all electromagnetic waves.

These waves can be shown on ropes and springs. Tie one end and wiggle from the other. $ope or Spring would move up and down

while you would observe motion going forward.

http:www.youtube.comwatch!v"&0cse1(2Ato

5toms of the robe are moving at @;;to the direction of wave motion. 5s shown below
http://www.youtube.com/watch?v=UHcse1jJAtohttp://www.youtube.com/watch?v=UHcse1jJAto


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Graphical Comparison Of Longitudinal And Transverse Waves.

3ey difference stems out from their definitions i.e. in longitudinal wave, particles move parallel while in transverse waves

particles move perpendicular to the direction of wave motion.

n transverse waves there are regions of crest and trough while in longitudinal waves there are regions of compression and

rarefaction.

n graphical way these regions can be related to each other in this fashion

watch the following video

http:www.youtube.comwatch!v"$buhdo4A56&

Some mportant Stuff about WA7%S:

0ow movement of wave is shown!
http://www.youtube.com/watch?v=Rbuhdo0AZDUhttp://www.youtube.com/watch?v=Rbuhdo0AZDU


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t is difficult to draw many longitudinal and transverse wave to shown the movement of the waves. nstead we draw $ays

*arrows to show direction of the travel)8 also we draw wavefronts *lines perpendicular to the to the rays). Wavefronts could

be spherical or linear but they always intersect at 944to the rays. The distance between two consecutive wavefronts is called

wavelength.

wavefronts and rays. 'oo at the following video

http:www.acoustics.salford.ac.ufeschoolswavesdripvideo.htm

The video shows the production of waves by a single droplet. The waves produced spread out in all directions in a circular

fashion. The circular parts are called the crest of the wave.

We use two diagrams one to show the increasingly outward moving cirular rings *crest of waves)--- called wavefronts and a

diagram to show the direction of movement of these waves-- rays.

#ircular wavefronts are drawn to show for all directions. Some time drawing of circular wavefronts is not suitable we (ustneed to draw lane wavefront for one direction only.

The distance between two consecutive wavefronts is called one wavelength. ;ou will encounter wavefront in reflection,

refraction and diffraction of waves. 'oo at the following video if you are more curious.

http:www.youtube.comwatch!v"


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(e) descri'e the use of a ri&&le tan* to show (1) reflection at a &lane surface, ($) refraction due to a change of s&eed at constant freuenc.

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(f) descri'e si"&le e&eri"ents to show the reflection and refraction of sound waves.

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(a) define the ter"s used in reflection including nor"al, angle of incidence and angle of reflection.

Law of reflection: 5ngle of incidence is alwas e0ual to the angle of reflection.

his law is alwas valid for on irregular surfaces as well.


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4n ter"s of wavefronts

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(') descri'e an e&eri"ent to illustrate the law of reflection.


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htt&:##edecelcie.co"#cieolevelsection+waves.ht"l6start-2download

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Ac) describe an e*periment to find the position and characteristics of an optical image formed b a plane mirror.

Loo" at the following animations

http:!!www.phsicsclassroom.com!mmedia!optics!ifpm.cfm

http:!!reflectionplanemirrors.wi"ispaces.com!

http:!!stwww.wei$mann.ac.il!lasers!laserweb!Bava!'irr2mge!2mageme1.htm

http:!!www.phsicstutorials.org!home!optics!reflectionoflight!planemirrorsandimageformationinplanemirrors

http:!!dev.phsicslab.org!Document.asp*4doctpe(Cfilename6eometricpticsEPlane'irrors.*ml

http:!!www.ph.ntnu.edu.tw!ntnu,ava!inde*.php4topic&;F.;

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(d) state that for reflection, the angle of incidence is eual to the angle of reflection and use this inconstructions, "easure"ents and calculations.

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(e) define the ter"s used in refraction including angle of incidence, angle of refraction and refractive inde.

5ngle of 2ncidence: The angle measured from the normal with which a ra hits the boundar between two mediums of different

densit.

5ngle of /efraction: The angle measured from the normal with which a ra enters a medium of different densit.

/efractive 2nde*: Propert of the medium!substance b which it can bring change in speed and direction of light waves.
http://edexcel-cie.com/cie-o-level-section-4-waves.html?start=9http://edexcel-cie.com/cie-o-level-section-4-waves.html?start=9http://www.physicsclassroom.com/mmedia/optics/ifpm.cfmhttp://reflection-plane-mirrors.wikispaces.com/http://stwww.weizmann.ac.il/lasers/laserweb/Java/MirrImge/Imageme1.htmhttp://www.physicstutorials.org/home/optics/reflection-of-light/plane-mirrors-and-image-formation-in-plane-mirrorshttp://dev.physicslab.org/Document.aspx?doctype=3&http://dev.physicslab.org/Document.aspx?doctype=3&http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=206.0http://edexcel-cie.com/cie-o-level-section-4-waves.html?start=9http://www.physicsclassroom.com/mmedia/optics/ifpm.cfmhttp://reflection-plane-mirrors.wikispaces.com/http://stwww.weizmann.ac.il/lasers/laserweb/Java/MirrImge/Imageme1.htmhttp://www.physicstutorials.org/home/optics/reflection-of-light/plane-mirrors-and-image-formation-in-plane-mirrorshttp://dev.physicslab.org/Document.aspx?doctype=3&http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=206.0


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(f) descri'e e&eri"ents to show refraction of light through glass 'loc*s.

7efine refraction:

3hen light passes from a medium of different densities then lightGs speed and direction changes. This change in direction and speed

of light is called refration.

This is due to refration of light that a pencil half dipped in water glass would appear distorted li"e the one shown below.

3hen light enters from less denser medium to more denser medium as shown below from air to glass.

2n terms of wavefront bending can be shown as


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2n this condition> from air to glassless denser medium to more denser medium> light will bend towards the normal. Normal line is the

reference line from which all angles are measured. 2tGs essential line.

#owever> when light moves from more denser to less denser medium then it will bend awa from normal.

2n above diagram> light ra is going awa from normal in glass.

#igher refractive inde* means larger bending.

8&&aratus:/ectangular glass bloc" with one face frosted> two ra bo*es> piece of paper.

Procedure:

o Place the glass bloc" on a piece of paper with the frosted side down.

o end two narrow ras of light through the glass bloc" as shown in fig.

o bserve the paths of the two ras of light.

o Har the angle of incidence I i I and measure the angle of refraction I r I.

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(g) do calculations using the euation sin i #sin r - constant.

3here I i I is the angle of incidence and I r I is the angle of refraction. I n I is refractive inde* of the material.


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(h) define the ter"s critical angle and total internal reflection.

%ritical 5ngle:

%ritical angle and total internal reflection is onl possible when light is travelling from denser to less denser medium. Jor e*ample:

from glass to air> glass to water> water to air etc.

Loo" at the figure above> light ras are coming from denser medium i.e. water and going into airless dense medium. 5s ou can see

that as the angle of incident is increased the refracted rasG angle would also increase and ras would start to bend towards the

surface. Loo" at the pin" ras > the left one is refracted at @; ;to the surface. The angle of incidence at which this happens is called

critical angle.

e!inition o! "ritical Angle#

"ritical angle i$ de!ined a$ the angle o! incidence%in den$er medium& !or 'hich the angle o! re!raction %in le$$ den$e

medium& i$ ())

Definition of Total 2nternal /eflection:

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(i) descri'e e&eri"ents to show total internal reflection.

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(9) descri'e the use of o&tical fi'res in teleco""unications and state the advantages of their use.


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&tical ;i'ers

ptical fibers are communication cables which carr information in the form of visible light waves. There are two parts of fiber optics

the inner part or centre which is called core and outer part called is cladding. These two parts have different refractive inde* and are

made of glass fibers which are easil bendable.

/efractive of inner partAcore) is greater than outer partAcladding). This is done so that light waves do not go out of the cable and can

totall internall reflected till it reaches its destination.

3h light waves> wh not sound waves are used to carr information4

Light waves can carr more information than sound because of their high fre0uenc. 2f ou were using sound waves to open KouTube

then ou have to wait for our hair to gre.

everal optical fiber cables are bundled together to ma"e a single cable.

Princi&le wor*ing of &tical ;i'er:

2t wor"s on the principle of Total 2nternal /eflection.

ow does it wor*6

Light is in,ected into the inner core of fiber at a certain angle where it bents towards the normal. This angle is chosen in such a wa

that it could ma"e critical angle inside. Then when it reaches claddingAouter part) which has smaller refractive inde* then instead of

going out of the fiber optics it totall internall reflects.


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2nside view or cross sectional view is shown below


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Uses of &tical ;i'er

1. 2lluminating models or road signs using onl one bulb

&. ndoscop seeing down inside a patientMs bod

(. %ommunications sending information along a light beam. Useful for telephone> television> radio> computer networ"s> stereo

lin"s> control in aircraft

+. ecurit fencing ver difficult to bpass

-. Jibre optic lamp

8dvantages of fi're o&tics over co&&er wire

1. %heap glass is made from silica> the basic constituent of sand

&. Light in weight useful in aircraft

(. Light beam can carr a huge amount of information

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(*) descri'e the action of thin lenses ('oth converging and diverging) on a 'ea" of light.

3hat are lenses4

Lenses are thin transparent material made up of glass> plastic etc.

3hen light passes through them the refract the light either to a single point or awa from the single point.

Tpes of Lenses:

There are two simple tpes of lenses

i %onve* lense ii %oncave lense

%onve* Lense: This lense is thic"er at the centre than at the edges.

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(l) define the ter" focal length.

Page $1 of 50


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(") it could be

1 /eal /eal 2mage is alwas formed behind the lense or opposite side to the position of the b,ect

& Hirtual Hirtual 2mage is alwas apparentl formed infront of lense or to the same side of the b,ect.

( ame si$ed as that of b,ect 2mage would have the same si$e i.e. height and width as that of the ob,ect.

+ 'agnified 2s larger than the si$e of the ob,ect

- Upright!rect 2f the ob,ectGs head is up then 2mage head would also be up.

F 2nverted!upside down 2f the ob,ectGs head is down then 2mage head would also be down.

and its focal length is reduced. 3hile> a thin lense is a wea" lense with a long focal length.

Note: 2gnore the thic"ness bte as this is not a part of the course.

(n) define the ter" linear "agnification and

Documents

Section 4 Waves