7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

1/13

Page 1

CNG N TP

Mn: L thuyt trng in tv Siu cao tn.

Lp: D11VT6.

I. Bi tp:

1. Cc bi tp v phn tnh in.

2. Phn x vkhc xsng in ttheo hng vung gc so vi b.

3. Tn sti hn cang dn sng tit din hnh chnht.

II. L thuyt.

1. Cc dng ca hphng trnh Macxoen. ngha ca hphng trnh Macxoen.

Dng Vi phn Dng Tch Phn Dng phc

1

2

3

4

1

2

3

4

1. 2.

ngha ca hphng trnh Maxoen:(1) M t mi quan h gia in trng v ttrng

+ Theo phng trnh Maxoen (1) (2), nu c 1 ttrng (in trng) bin thin theothi gian s to ra 1 in trng (ttrng) bin i theo khng gian v in ttrng c tnh cht xoy.+ Vai tr ca dng in dn v dng in dch l nh nhau trong qu trnh to ra t

trng xoy(2) M t quan h hnh hc:

+ lun chy lin tc.Trong t nhin khng c cc t tch l ngun sinh ra ttrng.

+ c th khng lin tc v trong t nhin tn ti cc in tch l ngunsinh ttrng.

(3) M t mi quan h gia trng in tv mi trngTheo phng trnh Maxoen (1), xoy ca ttrng lin quan n dng in dn (dngchuyn di ca vt cht) v quan h gia trng in tmi trng cht c th hin cc tham s:

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

2/13

Page 2

2. c im v cc phng trnh i vi trng in ttnh v trng in tdng, trng intbin th in.

Trng in ttnh:c im:

+ Cc i lng in v tkhng thay i theo thi gian, tc l o hm ring cc i lungca trng theo thi gian u bng khng + Khng c s chuyn ng ca cc ht mang in, ngha l mt dng in lun bng

khng: ( )H cc phng trnh Maxwell:

Trng in tdng:c im:

Phn b dng dnkhng i theo thi gian ( ). Do cc i lng ca trngcng khng i theo thi gian .Hcc phng trnh Maxwell:

Trng in tbin th in:

c im: Cc i lng in v tthay i theo thi gian .Hphng trnh Maxwell:

Tnh cht:+ in trng v ttrng u c tnh cht th.+ Chng khng c quan h trc tip vi nhau, tc l in

trng v ttrng c lp.

Tnh cht:+ xoy v ph thuc + thv c lp .

Tnh cht:+ v u xoy.+ v quan h cht ch.

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

3/13

Page 3

3. Nng lng ca trng in t-nh l Poynti ng.

* Nng lng ca trng in t:

Trong mt thtch V ty , trng in t sc nng lng tch t bng:

* nh l Poynti ng:

nh l Poynting thit lp mi lin h gia sthay i nng lng in t trong mt thtch V vidng nng lng in t chy qua mt kn S bao quanh th tch ny.

Trong : l cng sut tn hao di dng nhit ca dng in trong th tch V.

l VectPoynting: vectmt cng sut ca trng in t chy quan vin tch t vung gc.

(Du (-) vtri ca phng trnh th hin s bo ton nng lng).

Vi mi trng in mi l tng ( ):+ i ra khi mt kn S th > 0 < 0 nn nng lng trong V gim theo thi gian.+ i vo mt kn S th < 0 > 0 nn nng lng trong V tng theo thi gian.

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

4/13

Page 4

4. H in tng sng ca trng in tbin thin. Phng trnh sng.

* nh ngha sng:

- Sng l 1 hnh thi dao ng v chuyn ng ca 1 dng vt cht phn b lin tc trong khng gian.

- Tnh cht: Trong khi lan truyn th nng lng sng cng lan truyn theo v chiu truyn sng chnhl chiu truyn nng lng.

* Phng trnh sng: + Vi vt dn:

+ Vi in mi:

Vi l vn tc sng.

6. Phn loi kiu sng TEM , TE, TM .

- Sng in tngang (TEM) l sng c phng ca v vung gc vi phng z nn Ez=0 vHz=0.

- Sng in ngang (TE) l sng c

vung gc vi z. Ez=0, Hz0.

- Sng t ngang (TM ) l sng c vung gc vi z. Hz=0 v Ez0.

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

5/13

Page 5

5. Khi nim vsng in tphng, sng tr tr n vsng cu. Phng trnh v nghim caphngtrnh sng phng.

* Khi nim:

Trong khng gian ng nht, ng hng v rng v hn, sng in t s to ra ti mi im v mithi im cc vect in v tc bin v pha xc nh.

Nhng im ca trng c bin ging nhau hp thnh nhng mt ng bin, cn nhng im catrng c pha ging hp thnh mt ng pha. Trong khi sng lan truyn, mt ng pha cng dchchuyn .

Sng c mt ng pha trng vi mt ng bin gi l sng ng nht, cc mt ng nht c gi lmt sng. Nu mt ng pha v ng bin l nhng mt phng (mt tr, mt cu), ta c sng in tphng (sng tr, sng cu).

*Phng trnh sng phng:

Xt 1 sng TEM phng phn cc ng ch truyn theo z.

Hphng trnh Maxwell phc:

Gii hta c:

Gii phng trnh c nghim:

Thnh phn sng

ngc (Sng phnx)

Thnh phn sng

thun (Sng ti)

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

6/13

Page 6

7. Cc loi phn cc sng in t.

(1) Phn cc elip: u cui ca vect cng in trng ca sng vch nn hnh elip trong khnggian.

Bin i 2 biu thc trn, ta c:

y l phng trnh m tng cong elip trong mt phng ta E1, E2. Elip ny c trc ln tomt gc vi trc ta x. Do vy trong qu trnh truyn sng theo trc z u cui ca vect intrng ca sng tng hp s vch ra mt ng xon trong khng gian.

(2) Phn cc trn:

Khi thnh phn in trng ca hai sng thnh phn c bin bng nhau:

v lnh pha nhau gc = /2 th ta c:

Khi PT (*) trthnh: y l phng trnh ng trn trong mt phng ta E1, E2.

*

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

7/13

Page 7

7(tip)..

(3) Phn cc thng:

Sng c vectcng trng lun hng song song theo mt ng thng trong qu trnhtruyn sng gi l sng phn cc thng hay phn cc tuyn tnh.Trong trng hp ny gc lch pha ca 2 sng thnh phn v c gi tr: 0, , 2,Nn v phng trnh *) trv dng:

y l phng trnh ng thng i qua gc ta , nghing mt gc so vi trc x l .

i vi phn cc thng ty theo hng ca vect cng in trng, ngi ta cn phnlm hai trng hp l phn cc ngang v phn cc ng.

+ Sng phn cc ng (phn cc V): Trng hp ny vect ch c mt thnh phn theo phng x.+ Sng phn cc ngang (phn cc H): Trng hp ny vect

ch c mt thnh phn theo phng y.

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

8/13

Page 8

8. Sng in tphng trong cc mi trng:in mi l tng, mi trng vt dn (cc thng sca sng phng trong cc mi trng ny, vdng sng)

(1) Sng phng trong mi trng in mi l tng:

Vn tc pha l vn tc dch chuyn ca cc trng thi pha, hay vn tc dch chuyn ca mt ngpha.

=> vn tc pha bng vi vn tc sng, v n khng phu thuc vo tn s, mi trng nh vy ngita ni l mi trng khng tn sc.

d. Biu thc sng:

Theo nghim ca phng trnh sng phng (vi =j) ta c:

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

9/13

Page 9

V dng sng:

(2) Sng phng trong mi trng vt dn:

a. H s truyn sng:

Mi trng dn in tt l mi trng c rt ln, nn trong biu thc ca h struyn sng ta c thb qua thnh phn .

b. Vn tc pha.

Hay

=> Sng b suy hao.

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

10/13

Page 10

Vi vt dn tt ta thy phthuc vo tn s, mi trng nh vy ngi ta ni l mi trng tnsc.

c. Trkhng sng.

d. Biu thc sng.

Theo nghim ca phng trnh sng phng (vi =j):

V dng sng:

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

11/13

Page 11

9. Khi nim vnh hng ca hiung b mt.

Khi nim: Hiu ng b mt l khi dng in xoay chiu chy trn dy dn in lc ny mt dngin s tp trung ra st b mt ngoi ca vt dn. Khi tn s ca dng in cng tng th hin tngny xy ra cng mnh.

nh hng:

- Din tch tham gia dn in ca vt dn gim lm cho in trca vt dn tng ln, tn hao tng ln.

- in cm ca vt dn cng thay i.

10. Khi nim, phm ving dng ca cc ng truyn sng in t.

Khi nim:ng truyn sng in t l cc thit b hay h thng gii hn ng truyn lan ccdao ng in thay cc dng nng lng in ttheo hng cho.

ng truyn dng truyn dn nng lng siu cao tn hay sng siu cao gi l ng truyn nnglng siu cao tn (ng truyn siu cao).

ng truyn siu cao c gi l ng truyn ng nht nu nh dc theo hng truyn sng titdin ngang khng thay i v mi trng cha trong n l ng nht.

Phn loi v phm vi ng dng:

- ng truyn h: (ti tit din ngang khng c vng kim loi bao bc vng truyn nnglng siu cao tn)+ ng dy i (song hnh): Phm vi truyn sng di sng mt.+ mch di: phm vi truyn sng di milimet.+ ng truyn sng mt: phm vi truyn sng di milimet

- ng truyn kn: (c t nht mt mt vt dn kim loi bao bc hon ton vng truyn nnglng siu cao tn).+ ng dn sng ng trc: phm vi truyn sng di sng mt v decimet.+ ng dn sng ch nht: phm vi truyn sng di sng centimet.+ ng dn sng tr trn: phm vi truyn sng di sng centimet.

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

12/13

Page 12

11. Khi nim v hp cng hng, cc loi h s phm cht ca hp cng hng.

Khi nim: Hp cng hng l mt vng khng gian hu hn m trong n sau khong thi gian lnhn nhiu chu kdao ng siu cao tn c stch ly nng lng in t.

H s phm cht:

Cc loi h s phm cht:

W l nng lng ca trng in ttch ly trong hp.Pth l cng sut tiu hao trong hp l tn s cng hng ca dng dao ng.

7/27/2019 Cu h i n tp L thuyt trng in t v Siu cao tn

13/13

Page 13

12. Khi nim v mng nhiu cc siu cao tn.

* The document is only for reference. All changes can be made without prior notice!!! (Qu Ptit)