Answers to Grade 12U Physics Key Questions Unit 4 Lesson 13 Answers: 42. Using the two-dimensiona wa!e inter"erence #attern shown on the esson 13 "ie o" the 4th unit o" the course $P%4U& and the two e'uations in!o!ing #ath di""erence( com#ete the "oowing. a) *easure the wa!eength o" the wa!es( the distance +etween the sources( and the #ath distance "rom each o" the sources to the noda #oint shown on the diagram. $how the com#ete cacuation "or wa!eength. ,3 mars) +) $how the com#ete cacuation "or wa!eength o" the antinoda #oint shown on the diagram. ,3 mars) c) hat e""ect woud an increase in "re'uency ha!e on the inter"erence #attern/ ,1 mar) d) hat e""ect woud decreasing the distance +etween the wa!e sources ha!e on the inter"erence #attern/ ,1 mar) e) 0" the #hase o" the !i+rating sources was changed so that they were !i+rating com#etey out o" #hase( what e""ect woud this ha!e on the inter"erence #attern/ ,1 mar) $outions: a) he measured distance +etween the two sources is 1mm. he distance +etween source one and noda #oint 1( P 1 S 1 is 3mm( whie the distance +etween source two and noda #oint 1( P 1 S 2 is 4mm. ith these !aria+es we can now cacuate the wa!eength o" the wa!es. P 1, n ) S 1
=
3mm( P 1, n ) S 2
=
λ =
5 P 1, n ) S 1
4mm( d = 1mm 1mm( n = 2
/
− P 1, n ) S 2 5=
,3mm − 4mm)
=
,n −
,2 −
− 1mm = −1.λ
λ =
− 1 mm − 1 .
1 2
1 2
)λ
)λ
λ = .6mm
he wa!eength o" the wa!es is .6mm. +) P 1, m ) S 1
=
4mm( P 1, m ) S 2 λ =
5 P 1, m ) S 1
λ =
λ =
=
34mm ( m
=1
/
− P 1, m ) S 2 5=
5 P 1, m ) S 1
mλ
− P 1, m ) S 2
5
m , 4mm − 34mm) 1 λ = .mm
he wa!eength o" the antinoda #oint is .mm. he di""erences in wa!eength +etween the n ode and antinode is #ro+a+y due to a margin o" error when the distance measurements were made ,since it was done with a measuring ruer). c) An increase in "re'uency woud increase the amount o" inter"erence seen #er unit area on the #ane and there"ore noda and antinoda ines. d) 7ecreasing the distance +etween the wa!e sources woud decrease the amount o" inter"erence #er unit area o" #ane and thus reduce the noda and antinoda ines. e) 0" the sources !i+rate out o" #hase the nodes and antinodes woud interchange #ositions and create destructi!e inter"erence. 43. 0" you hear music in the distance( woud you +e more iey to hear the tre+e or the +ass notes o" the music/ Using your nowedge o" di""raction( e8#ain your answer. ,3 mars) $oution: 9or the situation descri+ed in the 'uestion a+o!e( one woud +e more iey to hear +ass notes +ecause +ass notes are ower "re'uency sounds than tre+e notes. As wa!eength is in!ersey #ro#ortiona to "re'uency( a ower "re'uency wa!e woud ha!e a higher wa!eength. e now "rom the #rinci#es o" di""raction that it increases with an increased in wa!eength( so a wa!e o" greater wa!eength woud resut in more d i""raction which in turn eads to wa!es ,in this case sound wa!es) s#reading out more "or #eo#e to hear. Un"ortunatey( 0 ha!e no #ro#er +asis on which to go to #ro!ide a +etter answer +ecause
the esson does not e8#ain how di""raction reates to the strength o" a sound wa!e. he a+o!e e8#anation can ony +e +ased on e8#erience that onger wa!es ,wa!es o" onger wa!eength) #ro#agate +etter than short wa!es. 44. &onsider the !ideo wired 24;6(< answer the "oowing 'uestion: %ow has +eing wired< with technoogy a""ected how you interact with society ,"or e8am#e( your thining( your reationshi#s( and the way you "unction daiy)/ 7o you thin that technoogica #rogress has +een "or the +etter/ hy or why not/ , mars) $oution: 0t is di""icut "or me to answer the a+o!e 'uestion +ecause 0 rarey use the internet to interact with other #eo#e. he ony way 0 interact with other #eo#e onine is +y emai and 0 ony use that to share and recei!e im#ortant in"ormation ,dates in time( uni!ersity a##ications( im#ortant e!ents( etc)= 0 do not use it to sociai>e. 0 o"ten use the com#uter to watch !ideos onine( #articuary the &?& series Murdoch Mysteries. Usage o" my com#uter has a negigi+e e""ect on my reationshi#s. @!era( 0 thin ad!ances in eectronic technoogy ha!e +een "or the +etter +ecause many o" the +ene"its e8ceed the costs. 9or e8am#e( now that most #eo#e ha!e i#hones( recent #oice +rutaity in the United $tates is recorda+e "or the courts and society to see( something unseen 3 years ago. Peo#e do get distracted 'uite o"ten +y these machines which do o"ten ead to such things as car coisions( +ut that can +e remedied +y +etter human udgement. 9urthermore( ha!ing an i#hone can ea!e a #erson we #re#ared "or an emergency +ecause he or she woud ha!e access to a #hone( camera( com#ass( timer ,"or ee#ing trac o" time as o##osed to timing onese")( thermometer( a ight( to a certain e8tent( and a source o" in"ormation in a de!ice that can con!enienty "it into a #ersonBs #ocet.
Lesson 14 Answers: 4. Per"orm the necessary research to identi"y three e8am#es o" industria a##ications that reate in some way to the inter"erence o" ight wa!es. 9or each e8am#e( descri+e a reated o+ or career. , mars) $oution: @ne industria a##ication that in!o!es the inter"erence o" ight wa!es is when &7 discs are made. A com#act disc is made o" a #oycar+onate wa"er coated in a n auminium aoy "im which is in turn coated in a #astic #oycar+onate coating that #artiay re"ects and #artiay transmits incident ight. Light rays re"ected "rom di""erent coating +oundaries inter"ere with each other to #roduce the coour"u #atterns< ,hin-"im inter"erence( n.d.). here"ore( the manu"acture o" &7 "or !ideo #ayers is a #ossi+e o+ "or someone wanting to s#eciai>e in an area in!o!ing inter"erence o" wa!es. Another a##ication o" inter"ering wa!es is in the use o" inter"erometers which are machines used "or measuring the sur"ace structure o" two o+ects ,0nter"erometry: *easuring with Light( n.d.) ,note in case this source is unre#uta+e or unreia+e this
we+site was checed ony to determine the usage o" inter"erometers). he de!ice wors +y sending +eams o" ight through arms<( +e"ore they hit a +eam s#itter to se#arate the two wa!es which are then re"ected +ac to the +eam s#itter +y mirrors and the two wa!es +ecome one again ,L0G@C( n.d.). 0nter"erence ,either constructi!e or destructi!e de#ending on i" the two wa!es are out o" #hase when they con!erge at the +eam s#itter) occurs when the two wa!es return a"ter +eing re"ected +y the mirrors. A #ossi+e career coud +e gained i" one were to +ecome a e8#erimentaist scientist or an engineer. @ne more a##ication o" inter"ering wa!es is in a "orm o" microsco#ic ithogra#hy( which is the use o" two or more inter"ering ight wa!es to generate #eriodic #atterns as an image "or the manu"acturing o" high-!oume semiconductors ,Dinci( 213). As such( a #ossi+e career where someone +ecomes "amiiar with the a##ication o" ight inter"erence is as a manu"acturer "or semiconductors in an eectronics com#any or ie Easin Dinci who wrote the artice sourced ust a+o!e( a scientist who studies wa!e inter"erence. $ources: &ai"ornia 0nstitute o" echnoogy( *assachusetts 0nstitute o" echnoogy. ,n.d.). L0G@: Laser 0nter"erometer Gra!itationa-a!e @+ser!atory. Fetrie!ed A#ri 2( 21 "rom L0G@ &atech we+site: htt#:;;www.igo.catech.edu;#age;what-isinter"erometer Dinci( E. ,213( uy 1). *icro;Hano Lithogra#hy( D8treme UI 0nter"erence Lithogra#hy: Progress and Pros#ects. Fetrie!ed A#ri 2( 21 "rom $P0D we+site: htt#:;;s#ie.org;newsroom;technica-artices;4J-e8treme-u!inter"erence-ithogra#hy-#rogress-and-#ros#ects ,n.a.). ,n.d.). hin-"im inter"erence. Fetrie!ed A#ri 2( 21 "rom: a+man.#hys(ut.edu;#hys222core;modues;mJ;hin "ims.htm ygo &or#oration. ,n.d.). 0nter"erometry: *easuring with Light. Fetrie!ed A#ri 2( 21 "rom D7U.#hotonics.com we+site: www.#hotonics.com;D7U;%and+oo.as#8/ A07M212
4. a) D8#ain why a #attern o" +right and dar "ringes is !isi+e on a screen when a ight is shone through a dou+e sit. ,4 mars) +) U#on using homas EoungBs dou+e-sit e8#eriment to o+tain measurements( the "oowing data were o+tained. Use these data to determine the wa!eength o" ight +eing used to create the inter"erence #attern. 7o this in three di""erent ways. , mars) •
he ange to the eighth ma8imum is1.12
•
he distance "rom the sits to the screen is 32 cm.
.
•
he distance "rom the "irst minimum to the "i"th minimum is 2.J cm.
•
he distance +etween the sits is .2 m.
$outions: a) hen a singe ight source o" a gi!en wa!eength is shone through a dou+e sit( di""raction occurs in which nodes and antinodes are generated +y constructi!e and destructi!e inter"erence when the wa!es "rom each sit o!era# and interact with each other. ?ecause two ight wa!es woud emerge "rom the di""erent sits there woud +e #oints where they are out o" #hase with each other( eading to destructi!e inter"erence whie at other #oints theyBre in #hase with each other. he ight "ringes woud re#resent the antinodes and the darer "ringes woud re#resent the nodes ,i" the wa!eength o" the source is changed or i" there are muti#e wa!eengths ie in white ight( one woud notice di""erent coours inter"ering in di""erent #aces). +) m
θ m = 1.12 =
K(
n
( L
=
=
32cm
=
3.2m( 4∆ x n
=
2.Jcm = .2Jm(
4
9irst *ethod λ =
Lλ
∆ x n =
λ =
d
∆ x n d
∆ x n =
∆ x n =
λ =
/
L
.2Jm 4
.636m
.636m ⋅ .2Jm 3.2m λ =
6.2 ⋅ 1 − m
$econd *ethod λ =
/
0t woud +e a sa"e assum#tion to concude that i" ∆ xn ∆ x m =
.636m.
=
.636m(
d = .24m(
dxm
mλ =
L
dxm
λ =
x m
x m
=
/
K∆x m
=
d K∆ x m
λ =
λ =
Lm
Lm
,.2Jm ⋅ ,K,.636m))) 3.2m,K) λ =
6.2 ⋅ 1 − m
λ =
/
hird *ethod
he #us sign in the +eow "ormua re#resents the "act that the distance +etween the "irst and "i"th minimums x n are gi!en the added distance to the centra ma8imum. dxn 1 ,n + )λ = 2 L xn
=
xn xn
=
1 2
)λ =
=
4.∆xn
4.,.636 m)
xn
,4 +
/
= .331K6m
,.2Jm),.331K6m) 3.2m
3.λ = 3.242 ⋅ 1 −4 m λ =
3.242 ⋅ 1 4.
−4
m
λ =
6.2 ⋅ 1 − m
here"ore( the wa!eength is 6.2 ⋅ 1 − m. 46. a) 0magine that you are conducting an acti!ity with a aser to create an inter"erence #attern. Use the a##ro#riate e'uations to #redict two ways ,other than the way descri+ed in the "oowing e8am#e) to change the inter"erence #attern in order to ha!e coser "ringes. D8#ain your #redictions. ,2 mars) %ereBs an e8am#e to get you started: According to the e'uation ∆ x =
Lλ d
(
the distance +etween the "ringes ,∆x) is #ro#ortiona to the wa!eength ,since they are +oth numerators). his means that increasing one wi increase the other. here"ore( decreasing the wa!eength wi decrease the distance +etween the "ringes. ,Hint: Eou can use the homas EoungBs 7ou+e-sit D8#eriment< simuation "rom this esson to !eri"y your #redictions.) +) 0" you were using a hands-on acti!ity to !eri"y your #redictions and use measurements to determine the wa!eength o" the aser +eing used( descri+e any sa"ety #recautions you woud tae and sources o" error that you might encounter. ?e sure to e8#ain how you might reduce the e""ects o" the sources o" error. ,3 mars) $outions: a) ?ased on the a+o!e e'uation: we can reduce the distance +etween "ringes +y increasing the distance +etween the two sits and;or reducing the distance +etween the sits and #roection +oard. +) A ree!ant sa"ety #recaution to tae woud +e to mae sure no+ody is in the area o" the e8#eriment without some "orm o" sa"ety gogges on +ecause !isi+e-ight asers can damage the human eye +y destroying an eyeBs #hotorece#tors ,the retina). @ne source o" error that coud occur in an e8#eriment is a sighty incorrect measurement o" the distance +etween sits ,that is +eing di""erent "rom that "irst cacuated theoreticay)( eading to a sight de!iation in the !aue o" the wa!eengths with each test. $ince sources o" error can not ogicay +e eiminated a together( one can ony reduce a source o" error and one way to do this is more care"u measurements o" the distance +etween sits and o" anges. Lesson 1 Answers: 4. &hoose a technoogy such as *P3 #ayers( asers( medica imaging( or ano ther that interests you ,other than the ce #hone). Fesearch the 0nternet and "ind out how it is reated to the #hysics o" ight and wa!es. 0n a##ro8imatey 1 to 1 words( write a
#aragra#h e8#aining the in +etween our understanding o" the aws o" #hysics and your chosen technoogy. D!auate how this technoogy has a""ected our daiy i!es. ?e sure to +rie"y descri+e the technoogy( its use( and its in to science. ,6 mars) $oution: @ne a##ication o" the #rinci#es o" re"raction is the re"racting teesco#e o" which there are two #rinci#e inds: the ceestia teesco#e and the terrestria teesco#e. A ceestia teesco#e has an o+ecti!e ens which +ends wa!es o" ight and sends them to an eye#iece "or o+ser!ation. hese teesco#es use enses o" great "oca ength which ca#tures a ma8imum amount o" ight maing an image cearer. e now "rom the #rinci#es o" #hysics that the arger a ens( the ess di""raction and inter"erence occurs and thus the +etter one can o+tain good resoution ,Du+an( Famsay( Ficard( 1J3). he disad!antage with ceestia teesco#es is that they o+tain an in!erted image. 9or use on Darth to see o+ects right side u#( one woud need a terrestria teesco#e which di""ers "rom a ceestia one in that it has a third ens to rein!ert an image once ca#tured +y the second ens ,Du+an( Famsay( Ficard( 1J3). ?eow are some +orrowed diagrams to iustrate:
$ources Du+an( %. L.( Famsay( . *.( Ficard( L. A. ,1J3). Basic Physics ,Fe!. ed.). oronto( @H: he *acmian &om#any o" &anada( Ltd.
?ecause the diagrams and a+o!e in"ormation were +orrowed "rom such an od +oo 0 ha!e cited the ,ony) section 0 +orrowed in"ormation "rom +eow to s#are the teacher the need to ocate a co#y o" the +oo and re!iew it "or its !aidity. 0n"ormation was +orrowed ony "rom the section under the heading The Telescope: a) Refracting Telescopes on #ages 2 and 21 as shown +eow:
4J. A aser emitting ight with a wa!eength o" nm is directed at a singe sit( #roducing an inter"erence #attern on a screen that is 3.m away. he centra ma8imum is . cm wide. ,1 mars) a) 7etermine the width o" the sit and the distance +etween adacent ma8ima. +) hat woud the e""ect on this #attern +e( i" i) the width o" the sit was smaer/ ii) the screen was mo!ed "urther away/ iii) a arger wa!eength o" ight was used/ c) %ow woud this inter"erence #attern di""er i" the ight was shone through a i) dou+e sit/ ii) di""raction grating/ $outions: a) λ = nm = . ⋅ 1 6 m( L −
∆ y =
=
3.m( 2∆ y
=
4.cm
/
2∆y
∆ y =
2
∆ y =
∆ y =
∆ y =
.cm 2 1m 2.cm, ) 1cm .24m
he distance +etween adacent ma8ima is there"ore .2m. w=/ λ =
w
w∆ y
=
L λ L ∆ y
w=
,. ⋅ 1
−6
m),3.m)
.2m
w = .6 ⋅ 1 − m
he width o" the sit is .6 ⋅ 1 − m. +) i) Harrowing a sit woud create more di""ractions( eading to more constructi!e and destructi!e inter"erence. 0t woud aso ead to +righter wider "ringes. ii) 0ncreasing the distance to the screen woud aso widen and +righter the "ringes. iii) Larger wa!eengths woud ead to an increase in di""ractions which woud increase the amount o" wa!e inter"erence. his woud in turn ead to wider +righter "ringes. c) i) 0" ight were shone through a dou+e sit( inter"erence "ringes woud a +e isoated( widey s#aced and "airy e!eny s#aced( and o" simiar intensities. ii) Using di""raction grating woud ead to "ewer "ringes that are narrower( +righter( and more e!eny and widey s#aced ,this "orms the +asis "or s#ectrosco#y). . Light "rom a aser with a wa!eength o" 6nm is directed at a di""raction grating o" 1ines;cm. 0" the di""raction grating is ocated 1. m "rom the screen( cacuate the distance +etween adacent +right "ringes. ,4 mars) $outions: λ = 6nm = 6. ⋅ 1
−6
m( linedensit y ∆ y =
λ =
∆ y =
= 1lines ; cm(
/
d ∆ y L λ L
d
d = / 1
d = ,linedensit y ) −
d =
1cm 1lines
d = .6 ⋅ 1
−6
1m cm, ) 1cm
L
= 1.m
d = .6 ⋅ 1 −J m ∆ y =
,6. ⋅ 1 −6 m),1.m)
∆ y =
.6 ⋅ 1 − m .16m
here"ore( the distance +etween the adacent +right "ringes is .16 m. Lenses o"ten contain thin coatings to reduce re"ections and UI radiation. D8#ain how this wors. ,4 mars) $oution:
taen "rom hy#er#hysics site htt#:;;hy#er#hysics.#hyastr.gsu.edu;h+ase;#hyo#t;antire".htm= name o" we+site is Anti-Reflection Coatings. he enses are coated with thin dieectric "ims which act as a sower medium through which the incoming ight has to tra!e through. $ome o" the wa!eets are re"ected on contact with the coating( +ut the rest tra!e through it and undergo re"raction. hey then are re"ected +ac through the "im in #arae with the wa!eets originay re"ected. ?ecause the wa!eets that are re"racted change in s#eed( they +ecome out o" #hase with the wa!es that are immediatey re"ected-eading to destructi!e inter"erence. his destructi!e inter"erence ensures the remo!a o" undesira+e re"ections and utra!ioet ight. Lesson 1 Answers:
2. 0magine that you had two #oari>ing "ims and were hoding them one on to# o" the other. hat woud the e""ect o" rotating the two #oari>ing "ims( with res#ect to one another( +e/ D8#ain what woud +e seen( and why. , mars) $oution:
he "irst "im in this case is taen to +e stationary and et us assume its #oari>ation direction #oints !erticay. here"ore( it a+sor+s the hori>ontay #oari>ed incoming #hotons and to some degree the non-!erticay #oari>ed #hotons. ?ut in "act( cose to N o" the #hotons reach the second "im des#ite the random #oari>ation with which they startedO As the second "im rotates- assuming it +egins with a #oari>ation direction that aso #oints !erticay ,#re"era+y seecting out #hotons aong its own a8is)( remo!ing more o" the initiay #re#ared #hotons unti it comes to an ange o" J ( when it "iters out a e8ce#t any hori>ontay #oari>ed # hotons. $ince there are none o" those #re#ared +y the "irst #oari>er to start with( we get tota darness at this #oint.
3. A ce #hone sends and recei!es eectromagnetic wa!es in the microwa!e "re'uency range. a) D8#ain the #hysics o" how an osciator creates these wa!es. , mars) +) Fesearch the #ossi+e side e""ects o" using ce #hones. &iting at east three we+sites that you consider reia+e( write a short 1- to 1-word #aragra#h summari>ing three main concusions +ased on your research and your o#inion= in other words( wi your ce #hone usage change( +ased on what you ha!e earned/ , mars) $outions: a) 0n order "or a radio transmitter ,ie those "ound in ce #hones) to send a signa( it needs a way to con!ert the 7& current "rom the ce #honeBs +attery into A&. An osciator can achie!e this= it contains an e' ui!aent to a tan circuit which is a ca#acitor and inductor in #arae that can change a currentBs eectric and magnetic "ied. he ca#acitor stores eectrostatic charge and the inductor stores magnetic "ieds. hen current enters the tan circuit the ca#acitor is charged +y the inductorBs coa#sing magnetic "ied. hen the ca#acitorBs eectric "ied dro#s as it charges the inductor as the current changes direction in the circuit. his changing magnetic "ied creates an osciating current( or A&. he current which now has a changing eectric and magnetic "ied is then sent across the air through an antenna ,note( a rea radio or ce #hone woud aso ha!e am#i"iers to increase the strength o" the signa and moduators to im#ress a signa onto a radio wa!e. systems anaogous to the tan circuit are used in todayBs ce #hones such as crystas since tan circuits are not !ery sta+e. +) here has +een concern as to whether or not ce-#hone usage can cause heath #ro+ems( #articuary cancer in the +rain. *uti#e studies in !arious countries ha!e concuded that there is not enough e!idence so "ar to su##ort this caim( +ut there is
agreement that more research needs to +e conducted in this area ,&euar Phones<( 214). 0t is aso admitted that the research d one on ce-#hone e""ects on heath are imited due to the "act that studies ha!e argey +een crude( not done o!er a ong enough #eriod o" time( and the "act that the technoogy is constanty changing ,&euar Phones<( 214). 0t has aso +een suggested that e8cessi!e ce-#hone usage can ead to eye damage. Pro" Le!i $chachter( who ed an 0sraei team that studied the e""ects o" o!eruse on mae ca" eyes ,which +are simiarities to those o" humans) "ound that o!er time e8cessi!e "ocus on ooing at #hones coud ead to +urred !ision and the de!eo#ment o" cataracts or #ermanent eye damage ,imonic( 2). @ne serious side e""ect o" o!eruse o" ce-#hones is that it is a distraction "or dri!ers which coud o" course ead to "ata accidents. A 1 car dri!ing study in Iirginia showed that ce-#hone usage contri+uted to 22N o" crashes and near-crashes ,athough com#ara+e data "or &anada is not a!aia+e) ,Foad $a"ety in &anada<( 214). 0t woud +e im#ossi+e "or me to gi!e an o#inion right now on how this woud a""ect my usage o" a ce-#hone as 0 do not currenty own one. $ources: American &ancer $ociety. ,214( 7ecem+er 12). &euar Phones. Fetrie!ed A#ri 2J( 21 "rom American &ancer $ociety we+site: htt#:;;www.cancer.org;cancer;cancercauses;othercarcinogens;athome;ceuar #hones Go!ernment o" &anada. ,214( uy 11). Foad $a"ety in &anada. Fetrie!ed A#ri 2J( 21 "rom Go!ernment o" &anada we+site: htt#:;;www.tc.gc.ca;eng;motor!ehicesa"ety;t#-t#114-121.htm
imonic( P. ,2( August J). *o+ie Phones can rigger Dye 7amage( 9ear $cientists. Fetrie!ed A#ri 2J( 21 "rom he eegra#h we+site: htt#:;;www.teegra#h.co.u;news;unews;3322132;*o+ie-#hones-can-triggereye-damage-"ear-scientists.htm
4. 0magine that you are maing wa!es in the scienti"ic community( in the "ied o" #hysics. As such( you ha!e +een gi!en the honour o" #resenting this yearBs echnoogy o" the Eear Award-and you get to choose the year and the technoogyO &hoose one o" the technoogies isted +eow and #re#are a #resentation o" a##ro8imatey 6 words to dei!er to your audience that incudes •
a s#eci"ic use o" the technoogy. ,1 mar)
•
a +rie" history o" its de!eo#ment. ,3 mars)
at east one a##ro#riate #icture or diagram that he#s e8#ain or iustrate your technoogy. ,2 mars) •
how this use o" technoogy has contri+uted to society and;or the en!ironment. ,2 mars) •
any chaenges that needed to +e( or sti need to +e( o!ercome and;or how this technoogy can +e e8#ected to +e de!eo#ed in the "uture. ,his can +e either "actua( as determined +y your research( or you can #ro!ide your own anaysis.) ,2 mars) •
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a citation o" sources. ,2 mars)
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accurate grammar and s#eing. ,2 mars)
Technology choices:
1. 2. 3. 4. . .
$#ectrosco#es $ur"ace #asmon #oaritons Go+a #ositioning system ,GP$) 7I7s Hight-!ision gogges ireess networs
6. 9i+re o#tics . Laser surgery J. Fadio transmitter 1. *icrowa!e emitter 11. -ray emitter
$oution: Fadio ransmitters and Fadar 7e!eo#ment @n this une ( in 1J41 we are gathered here at hiteha ,the ?ritish Pariament) to cee+rate the de!eo#ment o" the most im#ortant de!eo#ment o" our age( radio transmission and radar. ?ut "irst we must oo +ac on the history o" how this technoogy came to +e. he #rinci#es o" eectromagnetic wa!e motion were "irst aid down +y the $cotsman ames *a8we whose e'uations aid the "ounda tion "or radio transmission. Later( %einrich %ert> de!eo#ed the "irst sim#e radio transmitter in the 1s( "or whom the unit the %ert> was named. Later( in the 1Js the "irst radio +roadcasts were made +y the 0taian-+orn Dngish scientist Gugiemo *arconi. 0n 1J1( he sent the "irst transatantic signa "rom Hew"oundand to London. Fea radio transmission is "ar too com#icated to go into much detai o!er( +ut a sim#e radio transmitter re'uires "i!e ey com#onents( a #ower source( an osciator( a moduator( an antenna( and a micro#hone ,the atter i" sending !oice signas o!er the air). 0n the days o" %ert> and *arconi( s#ar ga#s were used as osciators +ecause +ringing a high !otage 7& #otentia to a ga# woud cause a ra#id coa#se in current and thus the magnetic "ied( creating A& ,reay #usating 7&) ,?erose( 1JJ4). ?eow are some "ascinating diagrams "or iustration #ur#oses:
0mage +orrowed +y ?erose( cited in te8t a+o!e. Later( +y ord ar 1( the !acuum tu+e had emerged and +y 1J3 had a +ut re#aced the s#ar ga# as an osciator. A !acuum tu+e actuay does not osciate the current( +ut rather acts as a !a!e( which "eeds energy to a tuned circuit which ra#idy changes the current and magnetic "ied in magnitude and direction-turning it into A& ,Gerrish( 1J6). he sim#est ind o" !a!e ,?ritish sang "or !acuum tu+e) is a diode( which is com#osed o" a heater( which e8cites eectrons to mo!e to an anode or #ositi!ey charged #ate a "iament or cathode( and a +ase to connect the !a!e< into a circuit. %owe!er( diodes are ony use"u as detectors= a rea osciator woud contain a triode instead. A triode is a diode with one added "eature( it has a grid which is used to am#i"y or strengthen the intensity o" a current. 0" a !otage is a##ied to the grid( which is usuay a s#ecia wire or wire mesh it eads to a direct change in the intensity o" the current running through the !a!e< ,Du+an( Famsay( Fichard( 1J3). his is use"u in changing the strength o" a signa( hence its use in am#i"iers. ?eow is a diagram o" a triode "or iustration #ur#oses:
he moduator is used to im#ress a signa u#on a wa!e. 9inay a micro#hone and antenna aow a !oice signa to +e sent o!er the air ,note( in the ord ar 1 era( !oice signas did not e8ist "or radio( signas were sent in *orse-code). A #articuary critica roe o" wireess teegra#hy ,eary radio) was "or communication +etween shi#s at sea and the and. ithout it( the F*$ Titanic woud not ha!e +een a+e to send out distress signas to the shi# that came to the aid o" its sur!i!ors( sa!ing hundreds o" i!es. ?y the midde o" the ast decade( radio signas( with the in!ention o" the cathode ray tu+e were +eing used to ocate and range "ind o+ects in the sy= radar had +een +orn. ?asicay( radar wors +y sending out a #use which hits an o+ect and is re"ected +ac to a radar antenna and sent to a #rocessor where the in"ormation "rom hitting a target is turned into a +i# on an osciosco#e ,radar screen). Last year( the e""ecti!eness o" radar was demonstrated +y the chain-home ser!ice o" Dngand to detect and identi"y German +om+ers "ying o!er ?ritain. his radica new technoogy he#ed 9ighter &ommand ,Foya Air 9orce) to turn the tide against the German war machine in their "inest hour<. An im#ro!ement on our current radar technoogy woud +e to #ro!ide oodown< ca#a+iity ,the a+iity "or radars to scan o+ects ceary n ear the ground without con"using it with ground cutter). his coud +e achie!ed +y somehow "itering out the #uses emitted +y ground cutter to ea!e desira+e targets on a screen. ithout radar( it is iey we woud ha!e ost the ?atte o" ?ritain( and so radar he#ed ee# the word sa"e "or democracy<. ?eow is a #icture o" the "amous 7o!er signa stations which he#ed contri+ute to ?ritish !ictory in the ?atte o" ?ritain:
A#oogies "or the crooed ange= thans and gratitude to the o#erators who wored round the coc in the radar stations to direct our #iots to the "ormations o" German +om+ers which +om+ed our country and to the +ra!ery o" the "ew< #iots who went u# e!ery day and rised their i!es to de"end our homeand. He!erC was so much owed +y so many to so "ew<.
$ources: ?ash. ,212( A#ri 2). ?atte o" ?ritain Femae on the &ards. Fetrie!ed *ay 1( 21 "rom 9oowing the Herd e+site: htt#:;;www."oowingthenerd.com;"tnRnews;+atte-o"-+ritain-remae-on-thecards;Ssthash.2hg>r+.d#+s
?erose( . $. ,21( 7ecem+er). he sounds o" a $#ar ransmitter: eegra#hy and ee#hony. Fetrie!ed *ay 1( 21 "rom Fadio $ciences &ommunications Fesearch &entre we+site: htt#:;;www.hammondmuseumo"radio.org;s#ar.htm 7enny( *. ,26). Blip Ping and Bu!! . ?atimore( *7: ohns %o#ins Uni!ersity Press. Du+an( %. L.( Famsay( . *.( Ficard( L. A. ,1J3). Basic Physics ,Fe!. ed.). oronto( @H: he *acmian &om#any o" &anada( Ltd. Gerrish( %. %. ,1J6). "lectricity and "lectronics. $outh %oand( 0L: he Goodyearico8 &o.( 0nc. Fo+inette( F. ,n.d.). %ow Guitar u+e Am#i"iers or. Fetrie!ed *ay 2( 21 "rom: htt#s:;;ro+ro+inette.com;%owRAm#sRor.htm Hote the "irst and ast we+sites isted were ony used to +orrow the #ictures "rom the internet.
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