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SNGSNGSNGSNGCc nguyn l cCc nguyn l cCc nguyn l cCc nguyn l c~~~~a nh sng, ia nh sng, ia nh sng, ia nh sng, in v Tn v Tn v Tn v T hhhhrrrrcccc

Paul FleisheTn Nghim dch______________

Pht hnh tdihttp://thuvienvatly.com

thng 8/2011


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NNNNi dungi dungi dungi dung

Gii thiu: Th no l mt nh lut t nhin? 1

1. Quang hrcCc nh lut v nh sng 4

2. Cc nh lut in t hrc 173. Dng in

nh lut Ohm v nh lut Joule 24

nh lut nghch o bnh phng 30

Theo dng lch s 33

Tiu s cc nh khoa hrc 35

Ti liu tham kho 41

Thut ng 43

V tc gi 44


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GiGiGiGii thii thii thii thiuuuu

ThThThTh no l mno l mno l mno l mt t t t nh lunh lunh lunh lut tt tt tt t nhin?nhin?nhin?nhin?

Mi ngi u bit mt iu lut l g. N l mt quy tc yu cu mingi phi hoc khng phi lm mt ci g . Cc iu lut cho chng ta bitrng chng ta khng nn li xe nhanh hn tc gii hn c php, rngchng ta khng c php ly ti sn ca ngi khc, rng chng ta phing thu thu nhp hng nm.

Nhng iu lut ny t u m c? nc M v nhng nc dn chkhc, cc iu lut c son ra bi nhng i biu c bu. Nhng nginy a ra tho lun nhng tng m h ngh l hp l v c ch. Sau , h

b phiu quyt nh nhng tng no s tht s tr thnh lut.

Nhng cn c mt loi lut khc na, l nh lut khoa hc. Th d,bn s c v nh lut Coulomb cui quyn sch ny. nh lut Coulombcho chng ta bit rng lc in gia hai vt bt k ph thuc vo hai yu t:lng in tch ca mi vt, v khong cch gia hai vt. Vy nh lutCoulomb t u m c, v chng ta c th lm g nu chng ta mun thay in?

nh lut Coulomb rt khc vi gii hn tc hay iu lut quy nhbn phi ng thu. Gii hn tc nhng ni khc nhau th khc nhau.Trn nhiu tuyn cao tc xuyn tnh, li xe c th chy n 105 km/h. Trnnhng tuyn ph ng c, h phi li xe chm li. Nhng lc in th luntc dng ging nh nhau cho d bn ang u ng qu hay thnh th, Php, Brazil hay M.

Thnh thong, ngi ta vi phm lut. Khi gii hn tc l 89 km/h,ngi ta thng li 97 km/h hoc thm ch cn nhanh hn. Nhng chuyn gs xy ra nu bn th vi phm nh lut Coulomb? Bn khng th. Nu bn

kim tra mt nghn vt tch in, bn s nhn thy mi v mi vt u tuntheo quy tc m t trong nh lut Coulomb. Mi vt u tun theo nh lutny. V chng ta bit rng nh lut Coulomb vn pht huy tc dng cho dngi ta c ang theo di vt hay khng.

nh lut Coulomb l mt nh lut t nhin, hay mt quy tc ca tnhin. Cc nh khoa hc v nh trit hc nghin cu nhng s kin xy ratrong th gii ca chng ta trong mt thi gian di. H tin hnh nhngquan st t m v lm nhiu th nghim. V h nhn thy nhng s kinnht nh xy ra mi mi theo mt kiu c quy lut, c th d on trc. C

l bn cng tng ch ti mt s dng thc ny trong th gii quanh ta.


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Mt nh lut khoa hc l mt pht biu gii thch vn vt hot ngnh th no trong v tr. N m t cch thc vn vt hot ng, ch khng

phi cch thc chng ta mun chng nh th. iu c ngha l mt nhlut khoa hc khng phi l ci g c th thay i h khi no chng ta la

chn. Chng ta c th thay i tc gii hn hay t sut thu nu chng tangh chng qu cao hoc qu thp. Nhng cho d chng ta c mun lc intc dng khc i nh th no chng na, th nh lut Coulomb vn pht huytc dng. Chng ta khng th thay i n; chng ta ch c th m t ci xy ram thi. Cng vic ca mt nh khoa hc l m t cc nh lut ca t nhincng ng v cng chnh xc cng tt.

Nhng nh lut m bn c trong tp sch ny l nhng nh lut vnvt. iu c ngha l chng khng nhng ng ti y, trn Tri t ny,m cn ng trong ton ci v tr. V tr bao gm tt c nhng th m chng

ta bit l tn ti: hnh tinh ca chng ta, h mt tri ca chng ta, thin h cachng ta, ton b hng t ngi sao v thin h khc, v ton b khong khnggian trng rng v tn gia chng. Ton b nhng bng chng m cc nhkhoa hc thu thp c v nhng hnh tinh v nhng ngi sao khc trong vtr ca chng ta cho chng ta bit rng nhng nh lut khoa hc p dngc cho Tri t ny cng p dng c cho mi ni khc.

Trong lch s khoa hc, mt s nh lut c tm thy qua nhngkhm ph xut sc ca mt c nhn no . Nhng thng thng, cc nhlut khoa hc c khm ph qua s n lc ca nhiu nh khoa hc, mi

ngi xy dng trn nn tng ca nhng ngi khc i trc. Khi mt nhkhoa hc nh Charles Augustin de Coulomb nhn c vinh d khm phra mt nh lut, th iu quan trng nn nh l nhng ngi khc cng cng gp cho s khm ph . Hu nh mi khm ph khoa hc u da trnnhng vn v nhng cu hi m nhiu nh khoa hc trc nghincu.

Cc nh lut khoa hc him khi thay i. Chng bt bin v chng tani v tr hnh x khc i. Cc nh lut khoa hc ch thay i khi chng tac thm nhng thng tin mi hay nhng quan st chnh xc hn. nh lut

thay i khi cc nh khoa hc c nhng khm ph mi cho thy nh lut ckhng cn m t v tr tt nh th na. H khi no cc nh khoa hc thngnht mt s thay i trong cc nh lut t nhin, th nh lut mi m t ccs kin mt cch hon chnh hn, hoc n gin v r rng hn.

Mt th d hay kiu ny l cc nh lut m t in hc v t hc. Ccnh khoa hc tng ngh rng in v t l hai hin tng khc nhau v tchri nhau. Nhng nhng khm ph mi v nhng php o ci tin gip chomt nh khoa hc ln, James Clerk Maxwell, vit li cc nh lut m t inv t hot ng nh th no. Maxwell nhn ra rng lc in v lc t l haidng khc nhau ca cng mt lc. Bn c th c v nhng khm ph caMaxwell phn sau tp sch ny.


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Cc nh lut t nhin thng c vit theo ngn ng ton hc. Ngnng ny cho php cc nh khoa hc chnh xc hn trong nhng m t ca hrng vn vt hot ng nh th no. Th d, nh lut Coulomb tht ra cvit nh th ny:

( ) ( )2

1 2q qF kd

=

ng ton hc lm bn hoa mt. N chnh l nh lut m t ccin tch tng tc nh th no. Vit nh lut ra nh th ny cho php ccnh khoa hc tnh ton chnh xc lc in tng tc trong nhiu tnh hungkhc nhau trn Tri t ny v mi ni trong v tr.

Ngnh khoa hc nghin cu vt cht v nng lng v cch thc chnghnh x c gi l vt l hc. Trong hng trm nm qua, cc nh vt l v

ang nghin cu v tr ca chng ta, h khm ph ra nhiu nh lut tnhin. Trong tp sch ny, bn s bt gp mt vi trong s nhng khm ph vi ny. S c mt s th nghim n gin bn c th thc hin nghimxem cc nh lut tc dng nh th no. Hy cng c v cng chia s nhngcu chuyn th v v nhng nh lut tit l nhng b n ca v tr ca chngta.


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Chng 1Chng 1Chng 1Chng 1Quang hQuang hQuang hQuang hrrrrcccc Cc Cc Cc Cc nh lunh lunh lunh lut vt vt vt v nh snnh snnh snnh sngggg

Khi chng ta ngm nhn bu tri m, chng ta thy nh sng pht ra thng nghn ngi sao khc nhau. Chng ta thy Mt trng v cc hnh tinhlung linh vi nh sng mt tri phn x. Ton b v tr ngp trong nh sng.

Nhng nh sng l g, v nhng nh lut t nhin no m t hnh trng can?

Ngnh vt l hc nghin cu nh sng c gi l quang hc. Mt snh khoa hc v i nht th gii, trong c Newton, Huygens, Maxwell vEinstein, nghin cu quang hc, n lc tm hiu cc nh lut v nh sng.

Mt nh lut m t hnh trng ca nh sng c ngi ta bit tihn hai nghn nm ri. Cc nh trit hc Hi Lp khng bit nh sng l ci g,nhng h tht s bit n truyn i theo ng thng. nh lut phn x nh

sngph thuc vo thc t ny. Khi nh sng bt ra khi mt ci gng hay

mt b mt khc, y c gi l s phn x. Khi bn nhn thy mnh tronggng l bn ang nhn nh sng phn x t mt ca bn n gng ri sau phn hi vo mt ca bn. nh lut phn x pht biu rng: Gc ti bngvi gc phn x.

Gc ti l gc ca nh sng chiu ln trn mt b mt phn chiu. Gcphn x l gc ca tia sng bt ra khi b mt . nh lut phn x pht biurng hai gc lun lun bng nhau. Nu nh sng chiu ln mt ci gng gc 45 , th n s phn x khi gng gc 45 . iu tng t lunng cho d nh sng chiu ln vi mt gc bng bao nhiu cng vy.

Bn c th d dng trng thy tc dng ca nh lut ny bng cch sdng mt ci gng nh, mt n pin dng flash, vi ming ba cng v bngdnh, thm mt t bi phn hoc bt m. V mt ng thng ln chnh giaming ba vung. Sau gp ming ba lm i theo ng v ny. Trnming ba th hai, t u thu knh ca n flash ln, v theo ng ra can. Ct dc theo ng ra mi v, sau khot mt ci l nh ngay chnhgia hnh mi ct. Dng n bc thu knh ca n flash li, dng keo dnhdn c nh lun. L nh s cho bn mt chm nh sng hp khi bn btn flash ln.


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Bn c th nhn thy ng i ca nh sng phn x bng cch ri bt mn vo trongkhng kh.

t ci gng ln trn bn. Dng ng ming ba gp np ln trnbn pha sau gng, ng gp np canh ngay khong gia ca gng.Ming ba ny s cho bn mt ng thng ng dng so snh gc ca ccchm tia sng. Ri mt lng rt nh bi phn hoc bt m vo trong khngkh lm cho chm sng n flash c th nhn thy r. ng ca phng vca s li, ri chiu nh sng ln chnh gia ca gng.

Lu chm nh sng phn x khi gng gc bng vi gc n i tigng. Cho d gc bn chiu chm sng flash l bao nhiu cng vy. Gc ca

nh sng phn x khi gng s lun lun khp vi gc nh sng chiu ti.nh sng truyn i theo ng thng. Nhng nh sng cng b cong

khi n truyn t mi trng trong sut ny sang mi trng trong sut khc.Nu bn dng mt ci bt ch vo trong cc nc, th ci bt ch trng nh bb cong khi n i vo trong nc.

Tt nhin, ci bt ch tht ra khng h b cong. N trng cong i v nhsng truyn vo nc b b cong. S b cong nh sng nh th ny c gil s khc x. Lu rng ci bt ch ch trng nh b cong ti b mt canc, cn trong nc v trong khng kh vn bnh thng. S khc x chxy ra ti ranh gii gia hai mi trng trong sut.


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Mi cht trong sut lm b cong nh sng nhng gc nht nh c thd on trc. S khc x xy ra v nh sng truyn i nhng tc khcnhau trong nhng cht khc nhau. Lng khc x ph thuc vo chnhlch tc nh sng trong hai mi trng trong sut . chnh lch tc

nh sng trong hai cht cng ln th nh sng s b b cong cng nhiu khi iqua gia chng.

nh sng truyn trong khng kh nhanh hn truyn trong nc. Khinh sng i t khng kh vo nc, n chuyn ng chm li. V v nchuyn ng chm li, nn n cn b khc x, hay b b cong. nh sngtruyn trong thy tinh cn chm hn na. Khi nh sng i t khng kh vothy tinh, n b cong nhiu hn na. Mt ci bt ch t mt phn pha saumt ming thy tinh dy s trng b cong nhiu hn so vi mt ci bt ch tmt phn trong nc.

Mt nh khoa hc tng nghin cu quang hc l Isaac Newton. Newtonbit rng khi nh sng mt tri b khc x trong mt lng knh thy tinh, thnh sng trng b phn tch thnh mt cu vng nh sng, gi l quang ph.

Newton chng minh rng nh sng mt tri tht ra gm ton b cc musc ca cu vng.

Nhiu nm sau ny, nh thin vn hc William Herschel pht hin ras tn ti ca mt loi nh sng khc nh sng khng nhn thy. Vo nm1800, Herschel ang tin hnh o nhit ca nhng mu sc khc nhautrong quang ph. ng mun tm hiu xem nh sng mu , cam, vng, lchay lam to ra nhiu nhit lng nht. ng s dng mt lng knh thy tinh phn tch nh sng mt tri thnh mt quang ph. Sau , ng dng mtnhit k o tng mu sc mt.

Mt s tng nhit bt ng dn Herschel n ch pht hin ra nh sng hng ngoikhng nhn thy.


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Ph in t bao gm nhng vng cc rng ca sng nh sng.


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Herschel nhn thy phn nng nht ca quang ph nm pha ngoi u, mt ni m ng khng th nhn thy cht nh sng no c! Nhng nhitk chng t rng c nhng tia sng khng nhn thy y. Herschel khm

ph ra s tn ti ca nh sng hng ngoi.

Mt nm sau, nh sng u bn kia ca quang ph c tm thy.nh sng ny cng khng th nhn thy, nhng n tht s to ra nh trn cctm knh nh. nh sng ny c gi l nh sng t ngoi. Vo gia th k 19,James Clerk Maxwell chng t rng quang ph nh sng cha nhiu hn cinh sng m chng ta c th nhn thy. Ngy nay, chng ta bit rng ton bquang ph khng ch c nh sng nhn thy, m cn c sng v tuyn, nhsng hng ngoi, nh sng t ngoi, tia X v tia gamma.

Nhng nghin cu ca Newton v nh sng vo cui th k 17 v uth k 18 lm pht sinh mt trong nhng cuc tranh ci dai dng nht trong

lch s khoa hc. Cuc tranh ci , khng phn thng bi trong hn hai trmnm tri, l v bn cht nh sng l mt cn ma gm nhng ht nh xu haynh sng l nhng lot sng.

tm hiu cu hi trn, bn cn phi bit mt cht v hnh trng casng. Sng c th d thy nht l trong mt b sng. to ra mt b sngti nh, bn cn c mt ci a to bng thy tinh trong, mt tm giy trng, vmt ci n bn. Bn cng cn c hai ci bt ch v vi ming g nh lm vt chn sng.

nc vo ngp hai phn ba ci a to. t n ln bn, pha trn mtming giy. t ci n bn sao cho nh sng ca n ri thng gc xungmt nc. Gi th dng ci u ty ca bt ch khu nh nc trong a to sng. Bn s thy sng to ra nhng ci bng trn t giy pha di, khinchng d thy hn. Hy nh rng sng m bn ang nhn thy l sng nc,nhng nhng sng khc, trong c nh sng, c nhng tnh cht tng t.

t mt ming g nh vo trong a lm vt chn sng. mt bn ca mingg, hy dng bt ch to ra sng. Hy quan st ci xy ra khi sng i qua vtcn.

Lu rng sng cong i xung quanh vt cn v truyn vo phn b bchn sng. S cong i nh th ny ca sng xung quanh mt vt cn c gil s nhiu x. Nhiu x l mt c trng ca mi loi sng.

i vi cc nh khoa hc hi th k 17, nh sng dng nh chngnhiu x ging nh nhng sng khc. nh sng c v truyn i theo ngthng, thay v cong vng quanh vt cn. Nu bn t mt vt vo trong nhsng mt tri, n to ra mt ci bng. Nu nh sng mt tri nhiu x gingnh sng nc, th bn ngh nh sng s i vng quanh qua vt v to ra mtci bng l m. Nhng nh sng mt tri to ra ci bng c ng bao sc nt.


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Trong b sng, sng nhiu x, hay cong i, xung quanh mt vt t trn ng i ca n.

V l do ny, Newton tin rng nh sng phi gm nhng ht nh xu,chuyn ng nhanh theo ng thng. Khi mt vt chn dng ht li, th ktqu l nhng ci bng sc nt.

Sau khi Newton xut rng nh sng gm nhng ht nh xu, hai nhkhoa hc ting tm khc khng tn thnh. Robert Hooke v ChristiaanHuygens cho rng nh sng cng hnh x ging nh sng. Chng ta hy trli b sng chng t lp lun ny ca h.

Chn mt phn trong ci b sng ca bn, ch cha mt l nh thng

qua phn b bn kia. Vi ci bt ch ca mnh, bn hy to ra sng trong phnb chn kn ca b. Lu ci xy ra khi chng i qua l nh.

Sng i qua ci l nh phn tn ra y ht nh cch chng lan ta ra tchnh ngun pht sng. Huygens lu rng bt k mi im trn phngtruyn sng c th tc dng nh mt ngun pht sng mi. Sng pht ra tngun mi ny s c nhng c trng ging vi sng ban u. Quy tc nyc gi l nguyn l Huygens.


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Nu nh sng gm nhng ht nh, bn s mun thy nhng ci bng sc nt (nh trn).Nu nh sng l sng, bn s mun thy ci bng km sc nt hn (nh di).

chnh l ci xy ra khi bn cho php nh sng chiu qua mt ci lnh. N lan ta ra t ci l, c nh l ci l l mt ngun pht sng.

Huygens cn trnh by rng nu nh sng l sng, th iu s giithch tnh cht khc x ca n. Sng nh sng truyn trong nhng cht liu

khc nhau s c tc khc nhau. S thay i tc s lm cho sng b bcong i. Vic l gii ti sao cc ht nh sng b b cong khi chng i vonc hoc thy tinh th kh khn hn.


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Trong mt b sng, sng truyn qua mt ci l nh phn tn ra nh th ci l nh l mtngun pht sng tht s.

nh sng i qua mt ci l nh hnh x nh th bn thn ci l l mt ngun sng.


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Sng cn c mt hnh trng th v khc gi l s giao thoa. nhnthy s giao thoa trong b sng ca mnh, bn s cn to sng vi hai ci btch. Gi hai ci bt ch cch nhau vi cm. Sau , khu mt nc vi c hai

bt ch cng lc, theo kiu u n, to ra hai tp hp sng.

khi hai tp hp sng chng ln ln nhau v i qua nhau, chngtng tc vi nhau. mt s ch, chng trit tiu ln nhau, cn mt s chkhc th chng cng gp tc dng ca chng vi nhau. Hin tng ny gi lgiao thoa sng. Nu bn gi kiu sng u vi chuyn ng u ca hai ci

bt ch, th bn s c h vn giao thoa u n.

Mt c trng ca sng l chng to ra h vn giao thoa khi chngchng ln nhau. Khi nhng dng ht giao nhau, ci ngi ta mun thy lchng va chm nhau. Khng ai tng quan st thy s va chm khi hai chmnh sng chiu xuyn qua nhau. Nhng nh sng c to ra giao thoa hay

khng?

Hai ngun sng to ra mt h vn giao thoa.

Nm 1801, nh vt l ngi Anh Thomas Young chng minh rngnh sng tht s nhiu x v tht s to ra h vn giao thoa, ging ht nhnhng sng khc. C v nh cu hi nh sng l ht hay l sng cui cng

c cu tr li.


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Bn c th d dng thy h vn giao thoa ca nh sng vi hai ci btch v n bn. Gi hai ci bt ch pha trc mt bn khi bn nhn v

pha ngn n. Di chuyn hai ci bt ch n gn nhau hn, cho n khichng gn nh chm vo nhau. Bn s nhn thy mt h gm nhng vch

sng v ti rt mn. l h vn giao thoa to ra khi nh sng pht ra t ngnn i qua khe hp chia tch gia hai ci bt ch. Nhng vch ti l nhng niti sng nh sng trit tiu nhau. V nh sng to ra h vn giao thoa gingnh nhng sng khc, nn n cng phi l sng.

Young cn tnh c kch c tht s ca sng nh sng. Bc sng casng nh sng l rt nh, nhng Young o c chng. Nhng mu scnh sng khc nhau ha ra l c bc sng khc nhau. Young tm thy bcsng ca nh sng mu vo khong 76 phn triu ca mt cm. Bc sngca nh sng mu lam cn nh hn na, khong 38 phn triu ca mt cm.

Nhng php o ca Young l gii ti sao s nhiu x nh sng li khnhn thy nh th. S nhiu x xy ra khi sng b cong vng quanh mt vtcn. Nhng sng nh sng qu nh nn chng ch c th b cong quanhnhng vt cn rt nh - nhng vt cn khng ln hn kch c nguyn t baonhiu.

Vo gia th k 19, ngi ta dng nh chc chn rng nh sng c bncht sng. Nhng ngay c khi vn vn cha c gii quyt xong.Khong nm 1900, nhng khm ph mi ca Max Planck v Albert Einstein lm hi sinh l thuyt ht. Kt qu cui cng ha ra l c hai phe tranh ciu ng! nh sng thng hnh x ging nh sng, nhng n cng tc dngging nh ht.

Sng c th c o bng bc sng hoc tn s ca chng.

C mt nh lut m t sng ca nh sng hay khng? C ch.

Nhng ngi sao m nht m chng ta thy trn bu tri m tht ra l nhngmt tri ang bng chy. nh sng ca chng m i nhiu sau hnh trnhng di ca chng n hnh tinh ca chng ta. Bn cng xa mt ngun


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pht sng, th rc r ca nh sng cng km i. Tht vy, cng canh sng pht ra t mi ngun sng gim rt nhanh khi khong cch nngun tng ln. gim t l vi bnh phng ca khong cch. Bnh

phng ca khong cch c ngha nhn khong cch vi chnh n.

Mi lin h c bit ny gia sng v khong cch n ngun sngc gi l quan h t l nghch bnh phng. Nhiu lc khc trong t nhingim i theo khong cch vi quy lut tng t. Mt li gii thch cn k hnnguyn do v sao xy ra nh vy, mi bn tham kho phn sau tp sch ny.Trong khi ch i, hy th ngh xem Mt tri ca chng ta cn to ra baonhiu nh sng. N cc k rc r, mc d chng ta cch xa n n 150 triukilomet!

Chng ta cn xt n mt thc t na v nh sng tc ca n.Galileo Galilei l nh khoa hc u tin n lc o tc ca nh sng. ng

ng trn mt ngn i, tay cm mt ci n lng y kn, v mt ngitr l ng mt ngn i ng xa, tay cm mt ci n lng ging nh vy.ng m n ca mnh ln. Ngay khi ngi tr l ca ng nhn thy nh sng,anh ta lp tc m n ca mnh ln. Galileo mun o thi gian cn thit ng nhn li tn hiu sng.

Tht khng may, th nghim khng thnh cng. nh sng c v truyni gia hai ngn i gn nh tc thi. nh sng chuyn ng nhanh n mcvic o tc ca n l v cng kh khn.

N lc u tin thnh cng trong vic o tc nh sng l s dngqu o ca Tri t lm thc o. Nh thin vn hc ngi an Mch OlausRmer bit s che khut ca cc v tinh ca Mc tinh xy ra theo lch nhhi cui th k 17. ng thy thi gian che khut bin thin, ty thuc voMc tinh v Tri t ni no trong qu o ca chng. Nu hai hnh tinh v hai pha ca Mt tri, th s che khut s mun vi ba pht. Nu hai hnhtinh cng mt pha ca Mt tri, th s che khut s sm vi ba pht.

Rmer nhn thy chnh lch thi gian c nguyn nhn l s chnhlch khong cch m nh sng t v tinh ca Mc tinh phi truyn i trc

khi n c nhn thy trn Tri t. Rmer bit ng knh gn ng caqu o Tri t. ng bit nh sng phi i thm bao xa bng qua qu o. Cho nn, ng c th c tnh nh sng truyn i bao nhanh bng quakhong cch . Rmer tnh c nh sng truyn i tc khong 226.000km mi giy.

Nm 1849, nh vt l ngi Php Armand Fizeau l khoa hc u tinch to ra mt dng c o tc nh sng trong mt th nghim trong

phng lab. K t , nhiu nh nghin cu khc tin hnh nhng php ongy mt chnh xc hn ca tc nh sng. Ni ting nht trong s hc l

nh vt l ngi M Albert Michelson. ng dnh phn ln cuc i camnh xc nh chnh xc tc ca nh sng, Michelson ginh gii thng


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Nobel nm 1907, gii thng tn vinh nhiu th nghim ti tnh m ng dng o tc nh sng cng chnh xc cng tt.

Rmer s dng nhng v tr khc nhau ca qu o Tri t o tc ca nh sngmt tri phn x khi Mc tinh.

Ngy nay, cc nh khoa hc t tc nh sng l 299.792,5 km/s, hay186.281,7 dm/s. Tc thng c lm trn l 300.000 km/s hay186.000 dm/s. y l mt s o rt quan trng. Tc ca nh sng c thxem l gii hn tc ca v tr. Nh chng ta bit, khng c ci g c th

truyn i nhanh hn tc nh sng.Tc ca nh sng l 300.000 km/s trong chn khng (khng gian

hon ton trng rng). nh sng truyn i trong khng kh nhanh gn nh th.Trong nhng cht liu khc, nh nc hoc thy tinh, tc nh sng chmhn nhiu. Th d, nh sng truyn i khong 225.000 km/s (140.000 dm/s) trong nc v khong 200.000 km/s (124.000 dm/s) trong thy tinh.Chnh s khc bit tc ny l nguyn nhn khin nh sng b khc x, hay

b b cong, khi n i t cht ny sang cht khc.

nh sng l mt b phn quen thuc trong th gii hng ngy ca

chng ta nn ngi ta thng d qun n c bit v quan trng nh th no.Chng ta c th nhn thy th gii ca mnh ch v n chm ngp trong mt


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dng nh sng lin tc, chng phn x khi nhng vt xung quanh chng tav i vo mt ca chng ta. V tr ngp trn nh sng truyn i tc htsc ln t nhng ngi sao v thin h xa xi. Chnh nh sng ny cho chngta bit ci g ngoi kia, bn ngoi th gii ca ring chng ta. nh sng l

kt ni quan trng nht ca chng ta vi mi th trong v tr nm bn ngoihnh tinh ca chng ta. Khng c kin thc v nh sng, th c l khoa hckhng th hiu c phn cn li ca v tr.


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bm cng ln trn o len. Qu bng s nhn mt t in tch m t o len.Nhng ci o len cng s nhn mt lng in tch dng ngang bng nhvy. Sau , qu bng s dnh vo tng do s chnh lch in tch giatng v qu bng.

iu tng t xy ra khi chng ta l chn trn thm tri nh vo mtngy kh hanh. Khi chng ta i trn thm, c th chng ta nhn mt lngin tch nh. Mt lng in tch bng nh vy nhng tri du to nn bntrong tm thm. Khi bn chm tay vo nm ca hay vt kim loi no khc,cc in tch trit tiu vi mt tia la in nh. Nu bn lm nh th trong

phng ti, bn s c th thy tia la in mt cch r rng.

iu quan trng nn nh l h khi no chng ta cp cho mt vt mtin tch m, th ng thi chng ta cng cho mt vt khc mt in tchdng. Ci o len nhn in tch dng ngang bng vi qu bng nhn in

tch m. Mi vt nhn mt in tch, v cc in tch cn bng vi nhau. lnh lut bo ton in tch.

Khm ph in hc tip theo do nh khoa hc ngi Php Charles-Augustin de Coulomb thc hin vo nm 1789. Coulomb bit rng cc intch tri du th ht nhau v cc in tch cng du th y nhau. ng mun o ln ca lc ht .

o lc in, Coulom treo mt thanh ngang bn di mt si dymng (Xem hnh bn di). Ti mi u thanh l mt qu cu tch in lm

bng kim loi. Sau , ng tch in tri du cho hai qu cu khc t gn .ng bit chnh xc mi qu cu c bao nhiu in tch. Bng cch o lngxon trn si dy, ng c th tnh ra lc ht gia nhng qu cu.

Cc kt qu ca Coulom tht bt ng v th v. ng khm ph ra lcin t l thun vi lng in tch hai vt v t l nghch vi bnh phngkhong cch ca chng.

Trc khi chng ta tip tc, iu quan trng l nn hiu t l thun v tl nghch ngha l g. Chng khng kh hiu nh tn gi ca chng gi ln.

Nu hai s o l t l thun, th khi mt s tng ln, s kia cng tngtheo. Th d, nu bn li xe vi tc 80 km/h, qung ng bn i t lthun vi thi gian bn li xe. Khi thi gian tng ln, qung ng cngtng ln. Bn li xe cng lu th qung ng bn i cng xa.

Nu hai s o l t l nghch, th khi mt s tng ln, s kia gim i. Thd, nu bn i mt hnh trnh di 160km, th thi gian ca chuyn i s t lnghch vi tc bn li xe. Bn li xe cng nhanh, th thi gian ca chuyni cng ngn. Khi tc tng ln, thi gian gim i.


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o lc in, Coulomb s dng nhng qu cu tch in treo bn di mt si dy mnh.

nh lut Coulomb cho chng ta bit rng lc in gia hai in tchph thuc vo ln ca hai in tch . chnh lch in tch gia haivt cng ln, th lc ht gia chng cng mnh. N cng c ngha l khi haivt cch xa nhau ra, th lc ht gim i nhanh. Nu hai vt chuyn ra xagp i, th lc ht ch bng mt phn t lc u. Nu chng chuyn ra xa gp

ba ln, th lc ht gim i chn ln.

V mt ton hc, nh lut Coulomb c vit nh sau:

Trong phng trnh ny, Fk hiu cho lc ht, q(1) v q(2) l in tch cahai vt, v dl khong cch gia hai vt. K l mt hng s, mt con s nhcho php tnh ra chnh xc lc ht in.

Coulomb cn lm th nghim vi lc t theo kiu tng t. Ha ra nh

lut ht t cng l mt nh lut nghch o bnh phng. Tht l ho hngkhi khm ph nhng lc khc nhau ny tun theo nhng nh lut ging nhau.


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N cho thy cc nh lut ca v tr phi khp vo mt khun mu n ginv c trt t.

Khm ph quan trng tip theo v in hc do Hans Christian rstedthc hin vo nm 1820. rsted thc hin khm ph ca ng mt cch tnh c.

ng ni mt si dy vi ngun cp in to ra mt dng in. Mt ci labn t trn bn th nghim gn . rsted thy khi dng in chy quady th kim la bn b ht v pha n.

Sau nhiu th nghim, rsted chc chn v khm ph ca ng: Mtin tch ang chuyn ng to ra mt t trng. H khi no c dng inchy trong dy th n to ra t trng xung quanh dy.

Bn c th t mnh lm th nghim rsted. Tt c nhng g bn cn lmt si dy di bc cch in, mt ci la bn nh v mt ngun cp in. S

dng pin kh 1,5V hoc pin n flash 6V.

Dng in chy qua dy dn to ra t trng, nh th nghim n gin ny cho thy.

Bc mt phn nh cht cch in ra khi mi u dy. Gn mt udy vi mt cc ca cc pin. B tr dy dn thnh vng v t ci la bn gn vng dy. Sp xp dy sao cho kim la bn khng hng thng v phady. Gi th chm u dy cn li vi cc kia ca pin. Quan st xem kim la

bn phn ng nh th no. Th lm th nghim vi kim la bn v vng dy vi v tr khc nhau. Mi ln khng nn dy ni vi c hai cc ca pin lu


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hn vi ba giy. Nu bn lm th, dng in s nhanh chng ly ht nnglng ra khi pin v si dy c th tr nn nng n mc nguy him.

Sau nm 1820, nghin cu in hc v t hc din ra vi tc rtnhanh. rsted nhn thy dng in c th tc dng lc lm cho kim la bn

quay. Nhng dng in mnh hn v nhng nam chm mnh hn c th kthp lm quay mt ng c. Khai thc khm ph ca rsted, nam chmin u tin v ng c in u tin c ch to ra vo nm 1823.

Nh khoa hc ngi Anh Michael Faraday thc hin ng gp quantrng tip theo cho s tm hiu dng in v nam chm. Faraday l mt nhthc nghim c khi. ng bit t th nghim ca rsted rng mt dngin ang chy c th to ra t trng. ng t hi liu ci ngc li c ngkhng? Mt nam chm c th gy ra mt dng in chy trong dy dn haykhng?

Cu tr li ca Faraday ha ra l mt trong nhng khm ph c ch nhttrong lch s khoa hc. Nm 1831, Faraday ch to ra mt mch in vimt cun dy. Trong mch in l mt in k, thit b dng o nhngdng in nh. Sau , Faraday t mt ci nam chm bn trong cun dy.ng pht hin thy mt dng in sinh ra h khi no ci nam chm di chuynvo hoc ra khi cun dy. Khi ci nam chm nm yn, khng c dng inno sinh ra ht. T th nghim ny dn n ci gi l nh lut Faraday: Mtt trng ang chuyn ng to ra mt dng in chy trong dy.

Ti sao khm ph ca Faraday li c ch nh th? Faraday nhanh chngnhn ra rng vic di chuyn mt si dy trong mt t trng mnh c th tora mt dng in. Cng nm , ng ch to ra my pht in t u tin.My pht ca Faraday c th sn sinh ra mt dng in u n khi cn nn. Pht minh ca Faraday khng ph thuc vo nhng ngun cung ha chtt tin, ln xn nh trng hp dng pin. V n khng bao gi cn kit nnglng. Nhng hu du khng l ngy nay ca my pht in u tin caFaraday sn xut in nng dng cho ti vi, t lnh, bng n in, v nhiuthit b in khc ca chng ta.

Nm 1864, James Clerk Maxwell ghp nhng mnh hnh in hc v thc li vi nhau. Cc nh lut in t hc ca ng c gi l h phngtrnh Maxwell. Pht biu ton hc ca nhng nh lut qu phc tp trnh by y, nhng nhng nh lut ca ng cho chng ta bit nhng iusau y:

Lc in v lc t l hai mt khc nhau ca cng mt lc. Mi in tch c mt in trng xung quanh n. in trng ny ht

in tch tri du v y in tch cng du.

Mt in tch ang chuyn ng hay mt in trng ang bin thinsinh ra mt t trng.


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Mt t trng bin thin sinh ra mt in trng.K t nm 1864, ht ln ny ti ln khc, cc th nghim chng t

cc nh lut Maxwell l ng. Do in v t ch l hai mt khc nhau cacng mt lc, nn cc nh khoa hc thng gi lc l lc in t. Cng

vi lc hp dn v lc ht nhn trong nguyn t, n l mt trong nhng lc cbn ca v tr.

Khi Maxwell xem xt khm ph ca ng, ng nhn ra mt ci g khc rt th v. Mt s bin thin in trng to ra mt s bin thin ttrng. Nhng s bin thin t trng sau li to ra s bin thin intrng. Qu trnh ny c th tip din mi mi. Nn mt s bin thin ca ttrng hoc in trng phn tn ra rt nhanh, to ra mt hiu ng sng int.

Maxwell tnh ra sng in t ny s chuyn ng trong khng giannhanh bao nhiu. Kt qu ca ng cho bit n truyn i tc chng300.000 km/s. Nhng l mt tc bit. l tc ca nh sng.Vy nh sng c th l mt dng nng lng in t hay khng?

Vng. Maxwell pht hin thy nh sng l mt sng in t. Nhng khm phtrong thi gian gn cho bit bc x nh sng tht s c pht ra bi sdao ng nhanh ca cc electron trong nguyn t.

Maxwell cn d on rng cc nh nghin cu s tm thy nhng loibc x in t khc nm ngoi vng nh sng nhn thy. Cc phng trnh

Maxwell cho bit phi c nhng sng in t c nng lng thp hn nhsng nhn thy, v nhng sng c nng lng cao hn.

Hai trong s nhng loi sng nh sng ny c bit n. nh snghng ngoi v nh sng t ngoi u c pht hin vo khong nm 1800.

Nhng tnh ton ca Maxwell cho thy nhng sng nh sng ny l nhngdng bc x in t ging nh sng nh sng vy. V khng bao lu sau khicc phng trnh Maxwell c thit lp, nhng dng bc x in t mi c khm ph ra.

Nm 1889, Heinrich Hertz pht hin ra s tn ti ca sng v tuyn.y l nhng sng in t c bc sng di hn nhiu so vi nh sng nhnthy. Nm 1895, Wilhelm Roentgen pht hin ra tia X. y l nhng sngin t c bc sng rt ngn. Ngng rng bc x trn t sng v tuyn,qua sng hng ngoi, nh sng nhn thy, nh sng t ngoi, v tia X v tiagamma c gi l ph in t. Tt c nhng tia khc nhau ny truyn i tc 300.000 km/s. Chng u hnh x ging nh sng nh sng. Cc tinon ca Maxwell v nng lng in t c chng minh l ng!

Nm 1897, J. J. Thomson pht hin ra s tn ti ca mt ht tch in

m nh hn nguyn t. Ht ny c gi l electron. Cc nh khoa hc nhnthy chuyn ng ca cc electron l ci mang nng lng in.


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Khi c xt mt qu bng trn vi len, mt s electron truyn t nhngsi len sang qu bng cao su. S truyn electron to ra in tch. Khichng ta ni mt si dy vi hai cc ca pin, chnh dng chy ca ccelectron mang dng in. V khi chng ta bt cng tc bng n, chnh

chuyn ng ca cc electron trong dy tc ca bng n to ra sng in tm chng ta gi l nh sng.

Tht kh tng tng cuc sng hin i s trng ra sao nu khng cin nng. Vic tm hiu lc in t mang n nhiu dng c hp dn.Chng ta s dng nng lng ny chy cc thit b trong nh, un si vthp sng nh ca, v tnh ton cc khon ngn qu gia nh. My vi tnh, ti vi,my ht a, radar, v c nghn dng c tuyt diu khc u ph thuc vokin thc ca chng ta v in t hc.


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Chng 3Chng 3Chng 3Chng 3

DngDngDngDng iiiinnnn nh lunh lunh lunh lut Ohm v t Ohm v t Ohm v t Ohm v nh lunh lunh lunh lut Joulet Joulet Joulet Joule

in nng tr thnh dng nng lng c s dng rng ri nhttrong th gii hin i ca chng ta. Nhng khai thc in nng, chng ta

phi bit n hot ng nh th no trong mt mch in. Vi kin thc ,cc thit b v dng bng in c th c thit k lm vic an ton vhiu qu.

Vo th k 19, ngi ta ngh dng in l mt dng chy ca nhngin tch qua bt k cht dn no, th d nh mt si dy. Ngy nay, chng tabit nhng in tch l nhng ht nh xu gi l electron. Nng lng intht ra l s chuyn ng ca cc electron trong mch in.

Mch in l ng dn qua dng in c th chy. N thng lmt lot dy dn v cc dng c in ni vi mt ngun cp in.

Nng lng in trong mch in do ngun in cung cp. Ngun nyc th l pin, thit b to ra nng lng in bng phn ng ha hc. Hoc nc th l my pht in to ra dng in bng cch cho cc dy dn chuyn

ng trong t trng. Cc cng ti in thng mi sn xut in bng nhngmy pht khng l hot ng bng sc nc, l than hoc du, hoc l phnng ht nhn.

Ngun in, hoc l my pht hoc l pin, to ra mt sut in ng.Bn c th ngh sut in ng l lng p sut in gi dng in i trongmch. Sut in ng trong mch c o bng n v volt (t theo tnAlessandrdo Volta, ngi pht minh ra pin).

Sut in ng thng c gi l hiu in th, hay n gin l th.

N ch to ra dng in khi no mch in ni vi cc dng v cc m cangun in l khp kn. Nu khng, n ch c th, hoc kh nng, to ra dngin. Mt cc pin 6 volt c 6 volt in th cho d n c ni hay khng ni vimt mch in.

Lng in tch chy qua mch in c gi l dng in. N co bng ampere (theo tn Andr-Marie Ampre, mt nh khoa hc khc nghin cu dng in). Ampere o s electron chy qua mch in trong migiy.

Hy nh rng dng in v in p l hai th khc nhau. C th c mt

dng in ln chy trong mch mc in p thp, hoc mt dng in nh


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chy in p rt cao. in p th o lc in, cn ampere th o tng inlng chy trong mch in.

Khi dng in chy trong mch in, n gp phi s cn tr. in tr lbt k ci g ngn cm hoc cn tr dng chy ca in trong mch. in

tr trong mch bin mt phn nng lng in thnh nhit lng. in trc o theo ohm (theo tn George Ohm, ngi chng ta s ni ti ngay

phn sau).

Mi th trong mch in, k c dy dn, u pht sinh in tr. Lngin tr trong mt mch in ph thuc vo bn yu t: chiu di ca mch,

b dy ca dy dn v nhng cht dn khc trong mch, loi cht liu cu tonn dy, v nhit ca mch.

Mt s dy dn, nh dy ng hoc dy bc, c in tr rt nh. Chng

dn in kh tt. Rt t nng lng in i qua dy ng b chuyn ha thnhnhit do in tr. l nguyn do ng thng c dng trong mch in.Nhng cht khc c in tr ln hn. Th d, dy Nichrome, cu to t hpcht ca nickel v chromium, c in tr rt ln. N tr nn rt nng khi dngin i qua n. V l do ny, Nichrome thng c dng lm b phn nungnng trong l nng hoc my sy tc.

Mt s cht liu, nh thy tinh v cao su, c in tr qu ln nn dngin chng th chy qua chng. Nhng cht liu nh th ny c gi l chtcch in.

Si dy cng di th in tr ca n cng ln. V dy cng dy th intr ca n cng nh. Ging nh nc chy qua mt ci ng ln, dng inchy qua vt dn dy thun li hn.

Nhit ca mt cht cng nh hng n in tr ca n. Trong a strng hp, in tr tng khi nhit tng. Nhng quy lut ny c ngoi l.

hiu r chuyn ng ca dng in trong mt mch in, hy hnhdung s tng ng gia mt mch in v h thng ng dn nc. Trong hthng nc, nc b buc chy qua cc ng do my bm. My bm tng

ng vi my pht in hoc pin trong mch in. My bm to ra p lc bucnc chuyn ng trong h. p lc ny tng ng vi sut in ng, hayin p. Lng nc chy trong cc ng tng ng vi lng in chy trongmch in.

in tr tng ng vi ma st (s c xt) trong cc ng dn nc.My bm phi khng ma st ny cho nc chuyn ng. Khi hai cht cxt ln nhau, s ma st sinh ra nhit. Ging nh ma st, in tr trong mchin to ra nhit. ng dn cng ln cho php nc chy cng d, trong khing nh c ma st cn tr dng nc ln hn. Dy dy c in tr nh hn

dy mng.


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Mt mch in c nhiu ci ging vi mt h thng dn nc khp kn.


30/4827

Vo u th k 19, nh vt l ngi c Georg Ohm nghin cu shot ng ca mch in. ng mun bit in tr v in p nh hng nhth no n dng in chy trong dy. Ohm nhn thy khi ng tng in ptrong mch ln, th dng in cng tng theo, min l nhng th khc trong

mch gi nguyn khng i. Gi s chng ta c mt mch in 10 volt vidng in 1 ampere chy qua n. Nu chng ta tng gp i in p ca mchln 20 volt, th chng ta s c dng in tng gp i ln 2 ampere.

Ohm cn pht hin thy dng in trong mch gim i khi ng tngin tr trong mch. Kt qu l ch c mt na ampere dng in chy quamch.

Nm 1827, Ohm cho cng b nhng kt qu ca ng. Nhng khm phny ngy nay gi l nh lut Ohm. nh lut Ohm c pht biu nh sau:Dng in trong mt mch in t l thun vi sut in ng (in p) v t

l nghch vi in tr.Hy ngh ti s so snh ca chng ta gia dng in v dng nc

chy mt ln na. Lng nc chy qua mt ci ng ph thuc vo p sutca nc v kch c ca ng. Nu my bm tng p sut (p sut cao gingvi in p cao), th nc s chy qua ng nhiu hn. Nu ci ng c tit dinmng hn (ng mng hn tng ng vi in tr ln hn), th nc chyqua n t hn. nh lut Ohm cho chng ta bit ci rt ging nh vy xy ravi dng in. Lng in chy trong mt mch ph thuc vo in p (psut in) v in tr ca mch.

V mt ton hc, nh lut Ohm c vit nh sau:

dng in = in p / in tr hayI=E/R

Trong phng trnh ny, I k hiu cho cng dng in, o theoampere. Ek hiu cho sut in ng, hay in p, ca mch. R k hiu choin tr.

Ch rng cng dng in (I) c biu din theo phn s. Nuchng ta tng in p (E) th t s ca phn s ln hn. Cho nn gi tr ca c

phn s ln hn. in p ln hn trong mch mang li dng in ln hn.Nhng khi chng ta tng in tr (R), th mu s ca phn s tr nn

ln hn. iu lm cho gi tr ca phn s nh i. in tr ln hn trongmch mang li dng in nh hn.

nh lut Ohm cho chng ta bit rng khi c rt nhiu in tr th dngin s chy rt t. Nu c in tr nh, th dng in s chy nhiu hn. iu gii thch ti sao ngi ta cm nhn nhng c sc in nguy him nht khida ca h b t.

Da kh l vt dn in khng tt. N c in tr ln. Cho nn khi mtngi c da kh bt ng chm tay vo dy dn v khp kn mch in, thdng in chy qua c th khng ln lm. Lng in c t nguy him.


31/4828

Nhng nu mt ngi ang b t, c bit khi ngi ang tip xc vimt vt dn tt nh nc hoc kim loi, th in tr nh hn nhiu ln. Ngi tr thnh mt vt dn tt hn nhiu, cho nn dng in chy qua c th lnhn, gy ra mt c sc nguy him.

Mt vi nm sau khi Georg Ohm thc hin khm ph ca ng, nh vtl ngi Anh James Joule t tin hnh nghin cu xem in nng hotng nh th no. Joule quan tm n vic lm th no mt dng nng lngny c th chuyn ha thnh mt dng nng lng khc. Mt trong nhng s

bin i m ng nghin cu l s chuyn ha in nng thnh nhit.

Cng sut l lng nng lng phn phi trong mi n v thi gian.Cng sut in o bng watt (theo tn James Watt, nh pht minh ra ng chi nc). Joule o cng sut do mch in phn phi bng cch kho stlng nhit m chng sinh ra trong mt lng thi gian nht nh. Phn ln

cng sut in trong nh ca chng ta c s dng theo kiu tng t - sinhnhit si m hoc nu chn thc n.

Joule nhn thy cng sut trong mt mch in ph thuc vo hai yut: in p ca mch v dng in chy trong n. Dng in chy trong mchcng ln th cng sut m n phn phi cng nhiu. V mch c in p cngln th cng sut m n phn phi cng ln. Cng sut do mt mch in sinhra c th tnh bng cch nhn in p vi cng dng in:

cng sut = in p cng dng in hayH=EI

Quy tc ny c gi l nh lut Joule. nh lut Joule cho chng tabit rng nu tng in p hoc cng dng in trong mch, th cng sutdo mch phn phi s tng ln.

Ton b nhng thit b in chng ta cm vo mch in gia dng us dng in nng thc hin cng. Chng bin i nng lng in thnhnhit, nh sng hoc chuyn ng. Cc thit b u a thm in tr votrong mch. Chnh in tr ca dy qun ca l in sinh ra in nng

bnh m ca chng ta hoc rn tht g cho bui ti. in tr c ch tm nytrong mch c gi l ti.

Cc ng c in trong my co ru, my git qun o, v my ht biu c in tr. Chng t mt ti tng dn ln mch in khi chng anghot ng. Nu bn t tay bn gn ng c in ca bt k thit b no, bns c th cm nhn nhit do in tr ca n sinh ra.

Trong mch in gia dng thng thng, in p lun lun gi nnh 110 hoc 220 volt. Nhng cng ti in s cung cp cho h tiu thlng dng in cho h s dng. Cho nn khi chng ta cn cng sut lnhn chy cc thit b ca mnh, th dng in trong mch tng ln. Trong

nh ca chng ta, khi chng ta s dng in cng sut ln hn, th chng tac nhiu ampere dng in hn chy trong mch in ca mnh.


32/4829

nh lut Joule gii thch ti sao mt l si in li tn km hn mtl nng bnh. L si in cn to ra nhit lng ln hn so vi l nng

bnh. Cho nn l si s dng dng in ln hn l nng bnh. Dng inln hn chy qua thit b cho cng sut ln hn, hay nhit sinh ra nhiu hn.

Nhng chng ta phi tr tin nng lng cho cng ti in. Cng sut chng tadng cng ln th chng ta phi tr tin cng nhiu.

nh lut Joule cng gii thch ti sao chng ta lp cu ch hoc cudao t ng vo mch in trong nh mnh. Khi chng ta lm mch in quti vi qu nhiu thit b, th cc dy dn phi mang dng in rt ln. Dydn c mt phn in tr i vi dng in, v in tr th sinh ra nhit. Dngin ln chy trong dy th nhit sinh ra cng nhiu. Nu cc dy dn qunng, chng c th d dng bt la.

S ngn mch xy ra khi hai dy dn trong mch chm nhau m

khng c thit b tiu th no trong mch. Hin tng c th xy ra nunh lp cch in bn ngoi dy b nng chy hoc trc v. Khng c intr ca thit b tiu th trong mch, mt dng in ln s d dng chy quady. Ton b dng in cn c th sinh nhit trong cc dy bt uchy.

May thay, mi mch in gia dng cn c lp cu ch hoc cu dao tng. Cu ch hot ng ging nh bt k mu dy dn no khc trong mchin. Chng dn in l mt phn ca mch in, v chng c mt phn intr. Chng cng nng ln khi dng in chy qua chng cng ln. Nhng cuch c thit k tan chy khi c dng in qu ln chy qua chng. Khicu ch tan chy, n ngt mch in. Khng cn dng in no chy na. Sngt mch nh th lm kt thc tnh trng qu ti in, nu khng th nhitsinh ra nng gy chy n. Cu dao t ng c vai tr bo v mchtng t nh vy, nhng khng cn phi thay chng sau mi ln bt.

Mi khi bn bt bng n ln, hoc nng bnh m, hoc l ci o smi, th nhng khm ph ca Georg Ohm, James Joule v nhng ng nghipca h li ang pht huy tc dng trc bn. Vic hiu r nh lut Ohm, nh

lut Joule v nhng nh lut khc ca mch in cho php cc k thut vinv k s in xy dng th gii in kh ha ca chng ta an ton v hiu qu.

Ngy nay, cc nh khoa hc hiu rt r s hot ng ca dng in.Nhng vn c nhiu th cn tm hiu thm v v tr. Chng ta vn phi hchi nhiu v cc ngi sao v hnh tinh, v nguyn t, v s k diu ca ssng. Vn cn nhng nh lut cn khm ph v nhng b n cn gii thch.C l mt ngy no bn s c th ghi thm tn ca mnh vo danh schnhng nh khoa hc gip khm ph ra nhng b n ca v tr.


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nh lunh lunh lunh lut nght nght nght nghch ch ch ch o bnh pho bnh pho bnh pho bnh phngngngng

Mt s nh lut t nhin quan trng u tun theo mt khun muchung. Khun mu ny c gi l nh lut nghch o bnh phng. Lchp dn hnh x theo kiu ny. Lc in v lc t cng th. Cng nhsng cng vy. Chng phi ngu nhin m nhng nh lut ny li ging nhau.Sau y l li gii thch ti sao nh lut nghch o bnh phng li p dngc cho qu nhiu loi lc khc nhau nh th.

Trong tt c nhng nh lut nghch o bnh phng, ln ca lcm nh lut m t t l nghch vi khong cch n ngun sinh ra lc. Khihai i lng l t l nghch, nu s o ny gim th s o kia s tng. lnca lc gim khi khong cch tng ln. Tuy nhin, trong tt c cc nh lutnghch o bnh phng, ln ca lc gim t l vi bnh phng khong

cch n tm ca lc.Cng nh sng tun theo mt nh lut nghch o bnh phng.Cng ca nh sng t l nghch vi bnh phng khong cch n ngunsng. Khi bn i ra mt ngun sng, sng ca nh sng pht ra t ngun gim i. Hy s dng nh sng lm th d xem ti sao c qu nhiu lckhc nhau li tun theo mt khun mu ny.

Hy tng tng mt ngun sng nh mt bng n in nh xu gia mt khng gian ln, ti en. nh sng t ngun ta ra mi hng, gingnh mt ci bong bng ang dn n. Cng nh sng c o theo n v

lumen. Gi s ngun sng ca chng ta ang sn sinh ra tng cng 1.000lumen nh sng.

Hy hnh dung mt mt cu vi bn knh 1 mt bao xung quanh ngunsng trn. nh sng t ngun pht ra ri sng phn bn trong ca mt cu.Hi nh sng phi ri sng din tch bng bao nhiu? Din tch b mt camt khi cu c tnh bng cch nhn 4 vi (pi, hay 3,14) nhn vi bnh

phng bn knh ca khi cu.

A = 4 r2

V th, khi cu ca chng ta c din tch b mt l 12,6 mt vung.1.000 lumen nh sng do bng n to ra s phn b u trn 12,6 mt vung

b mt .

Php chia tng lng nh sng cho s lng mt vung trn khi cu scho chng ta bit c bao nhiu nh sng ri ln mi mt vung. Khi chng tachia 1.000 lumen cho 12,6 mt vung, ta tm c mi mt vung c rikhong 80 lumen nh sng.

Gi s chng ta tng gp i bn knh ca mt cu bao xung quanh

ngun sng ca chng ta. Bn s thy rng 1.000 lumen nh sng s phn btrn mt din tch ln hn nhiu. Mt cu mi c bn knh 2 mt. tnhtng din tch b mt, mt ln na chng ta nhn 4 r2. Mt cu mi ca


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chng ta c din tch 50,2 mt vung. Bn knh ca mt cu mi ch gp ibn knh ca mt cu th nht. Nhng din tch ca mt cu th hai gp bnln din tch ca mt cu th nht. l v din tch ca mt cu c tnhtrn bnh phng ca bn knh.

Ngun sng ca chng ta vn ang to ra lng nh sng nh c: 1.000lumen. Nhng khong cch ny, lng nh sng nh c ang ri ln mtmt cu din tch 50,2 mt vung. Cho nn mi mt vung ch nhn khong20 lumen nh sng. Gi tr ny ch bng mt phn t lng nh sng m mimt vung nhn c mt cu th nht. Khong cch t ngun sng nmt cu tng ln hai ln, nhng cng nh sng ch cn bng mt phnt. y l mi lin h nghch o bnh phng.

iu tng t vn ng nu bn knh tng ln 3 mt. Mt ln nachng ta nhn 4 r2. Mt cu th ba ca chng ta c din tch b mt 113mt vung. Bn knh ca mt cu ny bng ba ln bn knh ca mt cu banu, nhng din tch ca mt cu th ba ln gp chn ln. 1.000 lumen nhsng ca chng ta phn tn trn 113 mt vung b mt. Mi mt vung thucmt cu th ba ca chng ta nhn khong 9 lumen nh sng. Gi tr ny bngmt phn chn lng nh sng m mi mt vung nhn c mt cu thnht. Khong cch t tm n mt cu gi tng ln ba ln, nhng cng nh sng ch bng mt phn chn.

Lng nh sng nh nhau, khi n ta ra t mt ngun, ri ln mt din tch mi lc mttng dn.

Tt nhin, nhng mt cu khng tht s tn ti. Nhng mt cutng tng cho chng ta mt cch hnh dung ti sao cng nh sng

gim nhanh hn nhiu khi khong cch tng ln. l v tng nng lngphi phn tn trn mt din tch tng ln nhanh chng.


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Thm ch, bn c th thy nh lut nghch o bnh phng ny xy ravi i mt ca bn. Hy nh du nhng khong cch 10, 20 v 30 mt tmt im 0 trong sn nh bn hoc trn va h gn nh bn. Khi tri ti, hyng trn im 0 ca bn. Nh mt ai ng vi mt n flash ti vch 10

mt. Hy nhn cng nh sng. Yu cu ngi di chuyn n vch 20mt, ri vch 30 mt, v so snh ci bn nhn thy. Mc d bn khng c khnng o cng nh sng nu nh trong tay bn khng c mt my o nhsng rt nhy, nhng bn s c th ni cng nh sng gim i nhanh khingi h tr bn di chuyn ra xa.

Bn c th hnh dung lc hp dn phn tn t tm ca Tri t (hay btk khi lng no khc) theo kiu ging nh nh sng ta ra t mt ngunsng. Bn c th hnh dung trng in t ta ra t mt ngun theo kiuging nh vy. Hy hnh dung mi lc ta ra t ngun ca n ging nh mt

ci bt dn n mi mi. Mi lin h nghch o bnh phng ng i vi ttc nhng lc ny bi v chng u phn tn u theo mi hng t tm imni chng sinh ra. Khi bn cng tin xa tm im , th tc dng ca nhnglc ny phn tn trn mt din tch ln hn nhiu.


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Theo dng lTheo dng lTheo dng lTheo dng lch sch sch sch s

1620 Tu Mayflower cp cng Massachusetts

1633 Galileo b Ta d gio kt n v buc qun thc ti nh1668 Issac Newton ch to knh thin vn phn x u tin

1678 Christiaan Huygens xut l thuyt sng nh sng

1687 Isaac Newton cho xut bn tc phmPrincipia

1692 Nhng th nghim ma thut din ra Salem, Massachusetts

1704 Isaac Newton xut bn cun Opticks, trong ng nu ra lthuyt ht nh sng

1732 Benjamin Franklin bt u xut bn cunPoor RichardsAlmanack

1752 Benjamin Franklin khm ph bn cht in ca tia st qua thnghim ci diu bay

1775-1783

Chin tranh ginh c lp ca nc M

1776 Tuyn ngn c lp ca nc M ra i

1789 George Washington tr thnh v tng thng u tin ca Hoa K

1800 William Herschel khm ph ra bc x hng ngoi; AlessandroVolta nu ra t bo in (pin)

1801 Johann Ritter khm ph ra bc x t ngoi

1801-1804

Thomas Young nghin cu nh sng v pht hin thy n tora h vn giao thoa

1820 Hans Christian rsted pht hin thy dng in sinh ra ttrng

1827 Georg Ohm cng b nh lut v mi lin h gia cng dng in, in p v in tr

1829 H thng ch ni ca Louis Braille dnh cho ngi m ln utin c cng b (hiu chnh vo nm 1837)

1831 Michael Faraday pht hin thy mt t trng ang binthin sinh ra mt dng in

1834 Charles Wheatstone o tc ca dng in trong dy dn

1849 Armand Fizeau o tc ca nh sng

1859 Charles Darwin cng b cun V ngun gc ca cc loi quaphng tin chn lc t nhin


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1861-1865

Cuc ni chin M

1864 H phng trnh Maxwell v in v t hc c cng b

1865 Tng thng Abraham Lincoln b m st

1876 Alexander Graham Bell ng k bng sng ch in thoi

1882 Trm pht in ca Thomas Edison New York bt u cung cpin nng cho khch hng cng nghip

1886-1889

Heinrich Hertz khm ph ra sng v tuyn

1895 Wilhelm Roentgen khm ph ra tia X

1897 J. J. Thomson pht hin ra electron

1905 Albert Einstein cng b l thuyt tng i c bit, trong ccng thcE= mc2

1914-1918

Th chin th nht

1922 Cng ti pht thanh Anh quc (BBC) thc hin bui pht thanh vtuyn cng cng u tin

1939-1945

Th chin th hai


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TiTiTiTiu su su su s cc nh khoa hcc nh khoa hcc nh khoa hcc nh khoa hrrrrcccc

Andr-Marie Ampre (17751836) l nh vt l ngi Php c

nng khiu ton hc biu hin t hi cn rt tr. Tr nh tt, kt hp nimam m c sch, cho php ng t nghin cu nhiu ti. Ampre sng lp lnh vc in t hc v l nh khoa hc u tin pht trin mt

phng php o dng in. Mc d s nghip khoa hc thnh cng xutchng, nhng cuc sng ring t ca ng c nhiu phin mun. Cha ca ng

b x chm khi ng mi 18 tui, ngi v th nht ca ng cht lc cn rttr, l cuc hn nhn ln th hai ca ng khng thnh cng.

Charles-Augustin de Coulomb (17361806) l nh khoa hcngi Php lm vic vi t cch k s qun s trong phn ln cuc i cang. Trong khi ti ng, ng c chn nm trn o Martinique thuc Ty n nhit i gip xy dng li nhng pho i b ph hy. Khi tr v Php,ng tip tc nghin cu trong ngnh vt l nhng ng thi cng bt unghin cu vt l. ng c bit ti nhiu nht vi nhng ng gp cho snghin cu lc in v lc t.

Albert Einstein (18791955) sinh ra c. ng l cu sinh vinthch c sch nhng khng thch nghe ging v lm bi kim tra, v th ngcha bao gi c thy dy ca mnh yu thch. Mnh bng tt nghip i

hc khng c g xut sc a ng n cng vic th k ca S cp bngsng ch Thy S. T nhng s khi u khim tn ny, ng i ti sng lp rathuyt tng i, ci lm thay i th gii vt l hc mi mi. Einstein b ngQuc x c xem l k th. ng l c vn khng chnh thc cho tng thngM Franklin D. Roosevelt v mi e da ca bom nguyn t. ng cn cmi lm tng thng Israel. Tuy nhin, trong cuc sng ring t ca mnh, ngkh trm tnh v gin d. Trong s nhng s thch ca ng l m nhc v ithuyn.

Michael Faraday (17911867) l nh ha hc v nh vt l ngi

Anh khm ph ra tnh yu khoa hc ca ng mt cch tnh c. Lm mtngi th ng sch n ngi cha th rn ngho kh ca mnh,Faraday thng c nhng quyn sch m ng ng tp. ng dn dn say msch vt l v ha hc. Nhng tip xc ny a n s khi u ca mt snghip v i, trong ng khm ph ra nh lut in phn, pht minh rang c in v my pht in, v thit lp nh lut mang tn ng v trngin t.

Armand Fizeau (18191896) l nh vt l ngi Php c nimam m c bit i vi lnh vc quang hc. ng nghin cu ngnh khoa hc

nhip nh mi ra i v vo nm 1845 tham gia tch cc vo vic chpnhng bc nh chi tit u tin ca Mt tri. ng cn nghin cu cch nh


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sng truyn qua nc, c nc tnh ln nc ang chy. Mt trong nhngthnh tu ni bt nht ca ng l vic o tc nh sng.

Benjamin Franklin (17061790) l mt chnh khch v tc giangi M. ng khng bt u nghin cu khoa hc cho n nm ng 40 tui,

nhng ng thc hin mt s tin b to ln nht vo thi i ca ng trongnghin cu in hc. Hin tng in ang rt thnh hnh vo gia th k th18, nhng Franklin lm cho vn nghim tc hn v tin hnh nhiuth nghim. L thuyt ca ng v in tch dng v in tch m v nh lut

bo ton in tch ca ng l nhng ng gp quan trng.

Galileo Galilei (15641642) cho i Pisa, Italy. ng l mttrong nhng nh khoa hc u tin xem thc nghim v ton hc l bn nghnh thit yu i vi quan st. S dng nhng cng c ny, ng thc hin

mt s khm ph v i, thng mu thun vi nhng c tin c chp nhnlu nay v a ng n ch mu thun vi nhng nh khoa hc khc v viGio hi Thin cha gio. ng c nhng bc tin b quan trng nhnggy tranh ci vi nhng th nghim mt phng nghing, bc b l thuyt caAristotle rng vt nng ri nhanh hn vt nh. Mt mu thun gay gt hnxy ra khi ng ng h m hnh nht tm ca Copernicus v h mt tri. V ldo ny, Galileo b Ta d gio kt n vo nm 1633 v b Gio hi qun thcti nh.

William Herschel (17381822) sinh ra c nhng nh c

Anh khi ng ln 9 tui. Mc d ng ni danh l mt nh thin vn hc, nhngngh nghip u tin ca ng l mt nhc s. Trong khi lm ngi nh nng Bath, nc Anh, s thch ca ng l ch to v s dng knh thin vn.ng pht hin ra hnh tinh Thin Vng tinh vo nm 1781, sau ngc b nhim lm nh thin vn hc cung nh cho nh vua George III.Herschel phn loi hng trm ngi sao, nhn ra Di Ngn h l mt thinh, v khm ph ra nh sng hng ngoi.

Heinrich Hertz (18571894) l nh vt l ngi c. ng l mtsinh vin xut sc c nhiu s trng nh kh nng ni lu lot mt s ngn

ng. trng i hc, lc u ng hc k thut, nhng nim am m chthc ca ng l vt l hc. ng tr thnh hc tr ca Hermann von Helmholtz Berlin. Di s thi thc ca Helmholtz, ng tp trung s ch vo bc xin t. Mt trong nhng kt qu quan trng nht ca nghin cu ca ng ls khm ph ra sng v tuyn.

Robert Hooke (16351703) l nh khoa hc ngi Anh lc u dnh vo nh th lm gio s nhng sc khe ca ng b nh gi l qu kmi vi cng vic . Mc d thng c nh ti l nh vt l vi nhngnghin cu nh nh lut n hi v nhng nghin cu ca ng v s hp dnv nh sng, nhng Hooke cn tri nghim thnh cng trong nhiu lnh vckhoa hc khc. L mt th ch to ti nng, ng pht trin hoc ci tin


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knh hin vi ghp, phong v biu v mt h thng in bo. ng cn nghincu ha hc, c bit l s chy, v cn ln sn sang sinh hc Hooke lngi u tin s dng thut ng t bo trong mt vn bn sinh vt hc.

Christiaan Huygens (16291695) ra i trong mt gia nh HLan giu c Hague. c o to khoa hc v ton hc, ng l mt trongnhiu nh vt l b thch v truyn cm hng bi bn cht ca nh sng.Vo nm 1678, Huygens xut l thuyt sng nh sng ca ng, tri vi lthuyt ht c Newton ng h; mi n sau khi c hai ngi h qua i th

bn cht lng tnh ca nh sng mi c ngi ta khm ph ra. Mt trongnhng ng gp to ln khc ca ng cho vt l hc l nghin cu ca ng vcon lc v ng dng ca n xc nh thi gian v lm ng h. Huygenscn am m thin vn hc; ng pht hin ra cc vnh v v tinh ln nhtca sao Th, v ng c nhiu l thuyt v s sng ngoi a cu.

James Prescott Joule (18181889) l nh vt l ngi Anh. ngl con trai ca mt nh sn xut ru bia Manchester, nc Anh. Lc cnnh, ng hay mc c v kh m yu nn ng c gia s dy km ti nh.Thy dy khoa hc v ton hc ca ng l nh vt l li lc John Dalton. Joulec bit yu thch nghin cu in hc v nhit, v ng tin hnh nhiu thnghim tng tng v th nghim t m. Nghin cu ca ng a n s thitlp nh lut Joule v dng in v in tr. ng cn ngi c cng i vinh lut bo ton nng lng.

James Clerk Maxwell (18311879) l nh vt l ngi Scotland,c o to Edinburgh, Scotland, v Cambridge, nc Anh. Mc d lcnh hay b tru chc v kh bn ln v lp d khi trng thnh, nhng ng tr thnh mt trong nhng tn tui li lc nht trong khoa hc. ng cng o bit ti vi nhng kt qu ca ng v trng in t (h phngtrnh Maxwell) v s ng gp ca ng cho thuyt ng hc cht kh.Maxwell cn nghin cu nhiu lnh vc a dng nh s m mu, nhip nh,v cc vnh sao Th.

Albert Michelson (18521931) cho i nc Ph (min bc

nc c v min bc Ba Lan ngy nay) nhng gia nh ca ng di csang M lc Michelson ln 4 tui. ng vo Vin hn lm Hi qun Annapolis, Maryland. L mt s quan, ng ging dy vt l v ha hc. Khinhim v ca ng i hi ng phi dy sinh vin cch o tc nh sng, ng t mnh i tm nhng phng php chnh xc hn tin hnh. Sau khi rihi qun, ng tr thnh mt gio s vt l. Nhiu th nghim quang hc cang, mt s tin hnh chung vi Edward Morley, gip a ti s pht trinthuyt tng i ca Einstein. Nm 1907, Michelson tr thnh ngi M utin nhn Gii Nobel vt l.

Isaac Newton (16421727) cho i Lincolnshire, nc Anh. Lmt sinh vin khc ngi khng quan tm n din mo bn ngoi, Newton l


41/4838

nh ton hc v nh khoa hc li lc. Ch mt vi trong s nhiu ng gpquan trng ca Newton cho khoa hc k ra gm nh lut vn vt hp dn, banh lut ca chuyn ng, nhng thnh phn c bn ca gii tch, v l thuytht nh sng. Newton cn l thanh tra v sau ny l gim c S c tin.

Nm 1705, ng c tn phong hip s, mt phn v s ci cch ca ng ivi nn tin t ca nc Anh. V cui i mnh, Newton t quan tm n ccvn khoa hc v ton hc, m chuyn sang nghin cu thut gi kim, thnhc v lch s.

Georg Ohm (17891854) ra i Erlangen, Bavaria (nc cngy nay) v hc khoa hc v ton hc ti trng i hc Erlangen. Ohm m tr thnh mt gio s li lc ti mt trng i hc c danh gi,nhng ng c nhiu nm lm tr ging b nh gi tng i thp nhiutrng. Khm ph ni ting nht ca ng, nh lut Ohm, pht biu rng

cng dng in t l thun vi in p v t l nghch vi in tr. V thunhp ca Ohm khng nhiu, nn khm ph quan trng ny c thc hinvi nhng thit b kh n gin v nhng dy dn kim loi t to! Ohm cnnghin cu cch tai ngi x l sng m. Nm 1849, cui cng ng trthnh gio s vt l Munich.

Hans Christian rsted (17771851) l nh vt l ngi anMch. Sau khi hc dc hc v khoa hc vt cht ti trng i hcCopenhagen, ng khng i vo s nghip nghin cu ngay. Trc tin, ng

b ra vi nm i du lch, ng thi vit lch v thuyt ging. Khm ph niting nht ca rsted, rng dng in to ra t trng, t nn tng chonghin cu in t hc.

Max Planck (18581947) l nh vt l ngi c. L mt sinh vinxut sc trong nhiu lnh vc, k c m nhc, Planck tr nn c bit hng thvi nghin cu nh sng. Nhng nghin cu ca ng v sng nh sng dnti khm ph ca ng v lng t nh sng, nhng gi nng lng ri rc tonn nh sng. Khm ph ny l mt cuc cch mng, mang li cho ng giithng Nobel v vch ra ranh gii gia vt l c in v vt l lng t.

Tri vi s nghip khoa hc thnh cng to ln ca ng, cuc i Planck cnhiu bi kch. V ca ng mt sau 22 nm chung sng, mt con trai b gittrong Th chin th nht, hai a con gi song sinh cht lc mi sinh, v mtngi con trai khc b hnh hnh trong Th chin th hai.

Wilhelm Roentgen (18451923) l nh vt l ngi c ban ud nh tr thnh mt k s. Trong khi hc tp Zurich, Thy S, ng tr nnam m hn i vi vt l hc v chuyn sang tt nghip lnh vc . Nm1895, Roentgen tin hnh nhng th nghim vi dng in cui cng ang n khm ph ra nhng tia b n khng nhn thy m ng t tn l tia X.

Roentgen nhn thy nhng tia X ny d dng i qua mt s cht nh g vgiy. Nhng cht khc, nh xng v kim loi, th chn tia X li. Nm 1901,ng c trao Gii Nobel vt l u tin cho khm ph ny.


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Olaus Rmer (16441710) l nh thin vn hc ngi an Mch.ng khng nh tn tui ca mnh vi vic xc nh rng nh sng c mttc hu hn. Nhiu nh khoa hc ng thi bt u tin rng nh sngkhng th c mt tc v hn, nh trc ngi ta ngh. Trong lc lm

vic ti i thin vn Paris Php, Rmer tr thnh ngi u tin chngminh l thuyt trn qua nhng quan st ca ng v s che khut ca nhng vtinh ca Mc tinh. ng o tc nh sng l khong 150.000 dm trn giy,chnh xc ng k so vi thi k y. Sau ny, ng tr v an Mch v vonm 1705 tr thnh th trng Copenhagen.

Joseph John (J. J.) Thomson (18561940) l nh vt l ngiAnh ban u d tnh tr thnh mt k s. Khi cha ca ng qua i vo nm1872, Thomson khng kh nng ng hc ph tr thnh thc tp vin vng chuyn sang hc ton v vt l. Sau khi tt nghip trng Trinity College

Cambridge, ng tr thnh gio s . ng tin hnh nghin cu rngv in t hc, a ti khm ph mang tnh cch mng ca ng v nhng htelectron. Nghin cu ca Thomson ha ra dn ti khm ph caRutherford v ht proton v s ra i ca ngnh vt l ht nhn. Thomson cnhiu th tiu khin. ng l mt fan trung thnh ca mn cricket v bng budc, v ng c bit thch cy xanh v lm vn.

Alessandro Volta (17451827) l nh vt l ngi Italy, lc cntr ng yu thch ngh thut hn l khoa hc. ng vit nhng bi thsonnet bng ting Italy v ting Php, v vit th ca ngi bng ting Latin.

Nm 19 tui, Volta tr nn yu thch khoa hc, c bit l in hc. ng tin hnh nhiu th nghim s dng in v pht minh ra mt s dng csn xut v o in tch tnh in. Tuy nhin, pht minh ni ting nht cang l pin, dng c sn xut dng in lin tc u tin ca th gii. Ngay c

Napoleon cng thy n tng. Nm 1801, ng ly tn Volta t cho mt btc x Lombardy (Italy ngy nay).

James Watt (17361819) l mt k s ngi Scotland. ng l mta tr m yu c vic hc nhiu ln b gin on do bnh tt. Tuy nhin, ng

vt qua tr thnh mt nh ch to thit b. Lc lm vic Glasgow,ng c yu cu sa cha mt ng c hi nc Newcomen, m hnh tintin nht vo thi y. Sau khi nghin cu c my, Watt b thuyt phc rngng c th tm ra mt thit k hiu qu hn. ng lm i tc vi mt nh snxut, v vi nm sau h tung ra mt ng c hi nc ci tin gi mt

phn vai tr quan trng trong cuc cch mng cng nghip. S s dng rngri ca n trong nh xng sn xut cho php ng ngh hu lm mt ngigiu c vo nm 1800.

Thomas Young (17731829) l nh khoa hc ngi Anh c ti

nng ht sc a dng. ng th hin s xut sc t rt sm, lc hai tui bitc. Ln 14 tui, ng hc 13 th ting v vit mt quyn t truyn bngting Latin. Gia nh ca Young khuyn khch ng tr thnh bc s. L mt


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sinh vin y khoa, ng nghin cu mt v c ch ca s nhn. Nhng am mny a ng n nghin cu quang hc. ng chng minh rng nh sngva nhiu x va to ra h vn giao thoa. Nhng kt qu ny gp phn vocuc tranh ci sng/ht xung quanh bn cht ca nh sng. Nm 1814, khi

tng Rosetta c mang t Ai Cp v London, Young nghin cu tng y cng vi nhng hc gi khc. ng gi mt vai tr quan trng trong vicgii m ch tng hnh c.


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Ti liTi liTi liTi liu tham khu tham khu tham khu tham khoooo

Asimov, Isaac.Asimovs Chronology of Science and Discovery. NewYork: HarperCollins, 1994.

Cobb, Vicki, v Josh Cobb.Light Action! Amazing Experiments withOptics. New York: HarperCollins, 1993.

Friedhoffer, Robert.Physics Lab in the Home. New York: FranklinWatts, 1997.

Gardner, Robert. Optics. New York: Twenty-First Century Books,1994.

. Science Projects about Electricity and Magnets. Springfield,NJ: Enslow Publishers, 1994.

Henderson, Harry, v Lisa Yount. The Scientific Revolution. San Diego:Lucent Books, 1996.

Lloyd, Gill, v David Jefferis. The History of Optics. New York:Thomson Learning, 1995.

Meadows, Jack. The Great Scientists. New York: Oxford UniversityPress, 1997.

Parker, Steve.Electricity. New York: Dorling Kindersley, 1992.

Skurzynski, Gloria. Waves: The Electromagnetic Universe. Washington,D.C.: The National Geographic Society, 1996.Spangenburg, Ray. The History of Science from the Ancient Greeks tothe Scientific Revolution. New York: Facts on File, 1993.

Wilkinson, Philip, v Michael Pollard. Scientists Who Changed theWorld. New York: Chelsea House Publishers, 1994.

Wood, Robert W. Who?: Famous Experiments for the Young Scientist.Philadelphia: Chelsea House Publishers, 1999.

WebsitesWebsitesWebsitesWebsites

BBC Online

Boston Museum of Science online exhibits

Center for History of Physics, American Institute of Physics

Cool Science, U.S. Department of Energy


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Kids Castle, Smithsonian Institution

NPRs Sounds Like Science

PBSs A Science Odyssey

San Franciscos Exploratorium

Science Museum of Minnesota


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ThuThuThuThut ngt ngt ngt ng

cng sut: tc phn phi nng lng, o theo watt

cng dng in: tc chy ca dng in, o theo amperein tr: ci cn tr hay khng li dng in trong mt mch in, o theoohm

nh lut bo ton in tch: vi mi in tch m c to ra, phi c mtlng in tch dng bng nh vy

nh lut Coulomb: lc in gia hai vt t l thun vi lng in tch haivt v t l nghch vi bnh phng khong cch ca chng

nh lut Faraday: mt t trng ang bin thin to ra mt dng in trongdy dn

nh lut Joule: tng dng in hoc in p trong mt mch in lm tngcng sut m mch to ra

nh lut Ohm: cng dng in trong mt mch in t l thun vi sutin ng v t l nghch vi in tr

nh lut phn x: gc hp bi mt sng vi mt b mt bng vi gc nphn x khi b mt

h phng trnh Maxwell: tp hp nhng nh lut ton hc m t lc inv lc t

nguyn l Huygens: mi im trn phng truyn sng tc dng nh mtngun pht sng mi c c im ging nh sng ban u

nhiu x: s cong ca mt sng xung quanh mt vt cn

ph in t: ton b ngng bc x in t, bao gm sng v tuyn, snghng ngoi, nh sng nhn thy, nh sng t ngoi, tia X v tia gamma

sut in ng: lc in gi mt dng in i vng quanh mch in, o

theo volt. Cn gi l hiu in ths khc x: s b cong ca mt sng ti ranh gii gia hai cht liu


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VVVV tc gitc gitc gitc gi

Paul Fleisher vit hn 20 tp sch cho gii tr v nh gio dc, nhChu k sng ca sinh vt bin ha, b schMng li ca s sng, vThc phm b no. Nhng tp sch xut bn gn y nht ca ng gmGorilla v Nhng iu th v v kem: Ci bn trong tha xc. Paul lcng tc vin thng xuyn ca tp ch Cng ngh v Hc tp. ngcn vit mt s phn mm gio dc, trong c phn mm tng tgii thngPerplexing Puzzles (Nhng cu hc ba).

Paul dy hc trong Chng trnh Nng khiu Richmond, Virginia, tnm 1978. ng cn tham gia nhng t chc cng dn hot ng v habnh v cng bng x hi. Nm 1988, ng nhn Gii thng v Habnh v Quan h quc t ca Hip hi Gio dc Virginia, v nm 1999ng c trao Huy chng Thomas Jefferson v nhng ng gp xutsc cho Gio dc Khoa hc T nhin. Lc rnh ri, mi ngi c th

bt gp Paul ang th b trong vn cy, ang lm vn, hoc cu c Vnh Chesapeake. Paul v v ca ng, b Debra Sims Fleisher, sng Richmond, Virginia.


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SNGSNGSNGSNGCc nguyn l cCc nguyn l cCc nguyn l cCc nguyn l c~~~~a nh sng, ia nh sng, ia nh sng, ia nh sng, in v Tn v Tn v Tn v T hhhhrrrrcccc

Paul FleisheTn Nghim dch______________

Pht hnh tdihttp://thuvienvatly.com

thng 8/2011

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