0_unde_electromagnetice

7/31/2019 0_unde_electromagnetice

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prof. Elena Rducanu, Colegiul Naional Bnean, Timioara

Unde electromagnetice


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Reactualizare

n jurul unui conductor parcurs de curent apare un cmp magnetic

Conductor liniar

Spir circular

http://www.youtube.com/watch?v=3KkOqVEa1oI&lr=1

Bobin
http://www.youtube.com/watch?v=3KkOqVEa1oI&lr=1http://www.youtube.com/watch?v=3KkOqVEa1oI&lr=1http://www.youtube.com/watch?v=3KkOqVEa1oI&lr=1


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Cmpul electromagnetic

Principiile teoriei cmpului electromagnetic

E

Bt

B

> 0n jurul unui cmp magnetic variabil n timpse genereaz un cmp electric variabil, alecrui linii de cmp sunt nchise

n anul 1864 fizicianul englez J.C.Maxwell a stabilit urmtoarele principii:

B

Et

E

> 0

+

-

n jurul unui cmp electric variabil n timpse genereaz un cmp magnetic variabil, alecrui linii de cmp sunt nchise

Ansamblul cmpurilor electric i magnetic, care oscileaz i se genereazreciproc, se numete cmp electromagnetic


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Unda electromagnetic

Forma de propagaren spaiu a cmpului electromagnetic se numete

und electromagnetic.

Undele electromagnetice transport energie la distan cu viteza v, caredepinde de proprietile electrice i magnetice ale mediului


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Cmpurile electric i magnetic din unda electromagnetic variaz periodicn timp:

x

T

tEEy 2sin0

x

T

tBBz 2sin0

Vectorii intensitate E a cmpului electric i inducie B a cmpului magneticsunt perpendiculari ntre ei i pe direcia de propagare

Vectorii intensitate E a cmpului electric i inducie B a cmpului magneticsunt n faz, ei trec simultan prin valorile maxime i minime


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Mrimi caracteristice undei electromagnetice

Viteza de propagare:

rrrr

c

B

Ev

00

11; c = 3 108 m/s

Densitatea volumic medie de energie electromagnetic:

2

2

2

1

2

1 BE

V

Ww elmelm

Intensitatea undei electromagneticeputerea medie transportat de und

n propagare prin unitatea de suprafa :

S

PI

med 2

m

WI SI

3

m

Jw

SIelm


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Simulri unda electromagnetic

http://www.youtube.com/watch?v=tbR93plA1WU&feature=related

http://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.html

http://www.walter-fendt.de/ph14ro/emwave_ro.htm

http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35
http://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.youtube.com/watch?v=tbR93plA1WU&feature=relatedhttp://www.youtube.com/watch?v=tbR93plA1WU&feature=relatedhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.walter-fendt.de/ph14ro/emwave_ro.htmhttp://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=35http://www.walter-fendt.de/ph14ro/emwave_ro.htmhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.amanogawa.com/archive/PlaneWave/PlaneWave-2.htmlhttp://www.youtube.com/watch?v=tbR93plA1WU&feature=relatedhttp://www.youtube.com/watch?v=tbR93plA1WU&feature=relatedhttp://www.walter-fendt.de/ph14ro/emwave_ro.htm


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Producerea undelor electromagnetice

Pentru producerea unei unde electromagnetice este necesar un

generator de oscilaii electromagneticeCel mai cunoscut circuit folosit pentru a radia n spaiu undeelectromagnetice este circuitul oscilant deschis alimentat de ungenerator de oscilaii electromagnetice

Pentru a obine un circuit oscilant deschisse ndeprteaz armturile condensatoruluii se ntind conductorii care leag bobina cucondensatorul ntr-o linie dreapt

Circuitul oscilant deschis se numete dipol

n jurul dipolului se genereaz i dispar,alternativ,cmp electric i cmp magnetic

http://www.youtube.com/watch?v=AfNWn8_xeL0
http://www.youtube.com/watch?v=AfNWn8_xeL0http://www.youtube.com/watch?v=AfNWn8_xeL0http://www.youtube.com/watch?v=AfNWn8_xeL0http://www.youtube.com/watch?v=AfNWn8_xeL0


10/18prof. Elena Rducanu, Colegiul Naional Bnean, Timioara

Antena

Este un dipol folosit pentru a emite sau pentru a capta

unde electromagnetice de o anumit frecven

Inductana i capacitatea unui conductor de antensunt uniform distribuite de-a lungul lui

Un conductor de anten cu lungimea de un metru arecapacitatea C = 5pF i inductana L = 3F.

n anten, se formeaz unde staionare de curent i de tensiune electric,cu ventre i noduri.

Oscilaiile electrice se propag de-a lungul antenei, se reflect la capetei interfer.

Antena, ca orice circuit oscilant are o frecven proprie , iar pentru caenergia undelor electromagnetice s aib valori mari, trebuie ca frecvenaoscilaiilor cu care este excitat antena s fie egal cu frecvena ei proprie


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2l

Cea mai simpl anten numit dipol semiund esteun fir conductor liniar n care se induc cureni inteni denalt frecven i se formeaz unde staionare, iar firulare lungimea egal cu jumtate din lungimea de undproprie

u

i

Intensitatea curentului variaz n lungul antenei i seformeaz unde staionare de curent

La capetele antenei se formeaz nod pentru intensitateacurentului i ventru pentru tensiunea electric

u

i

4l

Dac antena are un capt conectat la pmnt, laacest capt se formeaz nod pentru tensiuneaelectric fa de pmnt i ventru pentru intensitatea

curentului, iar la captul liber se formeaz nod pentruintensitatea curentului i ventru pentru tensiuneaelectric fa de pmnt

Lungimea acestei antene este egal cu un sfertdin lungimea de und proprie



Acordarea antenei

Dac antena trebuie s funcioneze pe diferite lungimi de und, este

necesar acordarea ei, adic s fie modificat corespunztor lungimeade und proprie.

pentru a mri lungimea de und proprie a unei antene, se introduce ncircuitul ei o bobin care are acelai efect ca i mrirea lungimii ei;

dac se conecteaz n serie cu antena un condensator,capacitatea totala circuitului de anten va scdea, lungimea de und proprie a antenei seva micora, ceea ce este echivalent cu scurtarea antenei

Ca

~ LC

n practic se introduce n circuitulantenei un condensator variabil pentrua acorda antena pe frecvena dorit



http://www.tutorvista.com/content/physics/physics-iv/communication-

systems/antenna.php
http://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.phphttp://www.tutorvista.com/content/physics/physics-iv/communication-systems/antenna.php


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Antene pentru internet wireless


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Antene pentru telefonie fix

Antene pentru televizor


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Anten de birou pentru

telefonie mobil

Antene auto


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Bibliografie

Gabriela Cone Manual clasa a XI-a, Editura Books Unlimited Publishing

George Enescu, Nicolae Gherbanovschi Manual clasa a XI-a, Editura Didacticasi Pedagogica 1994

www,google/images

http://www.youtube.com/watch?v=gfJG4M4wi1o&feature=related

http://www.youtube.com/watch?v=3KkOqVEa1oI&lr=1

http://www.youtube.com/watch?v=hajIIGHPeuU&feature=related

Octavian Rusu, C-tin Tristaru Manual clasa a XI-a, Editura Corint

Mircea Rusu, Mircea Nistor Manual clasa a XI-a, Editura Corint
http://www.youtube.com/watch?v=gfJG4M4wi1o&feature=relatedhttp://www.youtube.com/watch?v=3KkOqVEa1oI&lr=1http://www.youtube.com/watch?v=hajIIGHPeuU&feature=relatedhttp://www.youtube.com/watch?v=hajIIGHPeuU&feature=relatedhttp://www.youtube.com/watch?v=3KkOqVEa1oI&lr=1http://www.youtube.com/watch?v=gfJG4M4wi1o&feature=related

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