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El Magnetisme De La Terra Estudi De La Història Del Geomagnetisme I Mesura Del Camp Magnètic Al Laboratori El Magnetisme De La Terra

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El Magnetisme De La Terra Estudi De La Història Del Geomagnetisme I Mesura Del Camp Magnètic Al Laboratori El Magnetisme De La Terra COL·LECCIÓ JOVES INVESTIGADORS 17 COL·LECCIÓ JOVES INVESTIGADORS El magnetisme de la Terra Estudi de la història del geomagnetisme i mesura del camp magnètic al laboratori El magnetisme de la Terra Arwa Mehmood Wahid PREMI DE RECERCA MIQUEL17 SEGURA PREMI DE RECERCA MIQUEL17 SEGURA El magnetisme de la Terra Estudi de la història del geomagnetisme i mesura del camp magnètic al laboratori Arwa Mehmood Wahid Autora: Arwa Mehmood Wahid Edita: Ajuntament de Rubí Correcció de català: David Aguilar España Text revisat per: J. Marcos Fernández-Pradas. Professor Agregat en el Departament de Física Aplicada de la Universitat de Barcelona Disseny i maquetació: Masdisseny Edició digital: juny 2017 ÍNDEX PRÒLEG AGRAÏMENTS INTRODUCCIÓ 1. ESTUDI HISTÒRIC DEL GEOMAGNETISME 1.1 Edat antiga (3500 aC - 476 dC) 1.1.1 Cultura grecollatina 1.1.2 Cultura xinesa 1.1.3 Cultura olmeca 1.2 Edat mitjana (476-1492) 1.2.1 Orient 1.2.2. Occident 1.3 Edat moderna (1492-1789) 1.3.1 Segle XVI. Es detecten les primeres irregularitats 1.3.2 Segle XVII. El magnetisme segons Gilbert 1.3.3 Segle XVIII. Grans expedicions i els primers observatoris 1.4 Edat contemporània (del 1789 a l’actualitat) 1.4.1 Segle XIX. L’aparició de l’electromagnetisme 1.4.2 Segle XX. El començament de l’era espacial 1.4.3 Segle XXI. Una ciència en progrés 2. DESCRIPCIÓ DEL CAMP MAGNÈTIC TERRESTRE 2.1 El magnetisme 2.1.1 Els imants 2.1.2 Explicació del magnetisme natural 2.2 Estudi del camp magnètic 3 2.2.1 Descripció del camp magnètic 2.2.2 Representació d’un camp magnètic 2.2.3 Comportament de la matèria en els camps magnètics 2.2.4 Camp magnètic generat per un conductor elèctric 2.2.5 Moviment de partícules en un camp magnètic 2.3 El camp magnètic terrestre 2.3.1 Descripció del camp magnètic terrestre 2.3.2 Origen del camp magnètic terrestre 2.3.3 Cavitat geomagnètica o magnetosfera 2.3.4 Principals fenòmens magnètics 3. EXPERIMENTACIÓ AL LABORATORI 3.1. Construcció d’una bobina 3.1.1 Objectiu 3.1.2 Material 3.1.3 Procediment 3.1.4 Resultat 3.2 Creació d’un camp magnètic 3.2.1 Objectiu 3.2.2 Material 3.2.3 Fonament teòric 3.2.4 Procediment 3.2.5 Conclusió 3.3. Càlcul de la intensitat del camp magnètic terrestre amb una bobina 3.3.1 Objectiu 3.3.2 Material 3.3.3 Fonament teòric 3.3.4 Procediment 3.3.5 Errors 3.3.6 Conclusió 3.4. Mesura del camp magnètic terrestre amb la bobina de Helmholtz 3.4.1. Objectiu 3.4.2. Material 4 3.4.3. Fonament teòric 3.4.4 Procediment 3.4.5 Errors 3.4.6 Conclusió 4. COMPROVACIÓ DELS RESULTATS EXPERIMENTALS AMB DADES DE LA BIBLIOGRAFIA 5. CONCLUSIONS DEL TREBALL 6. OPINIÓ PERSONAL 7. BIBLIOGRAFIA I ALTRES FONTS D’INFORMACIÓ ANNEXOS Annex I. El descobriment de Richard Carrington Annex II. Temperatura de Curie Annex III. La ionosfera Annex IV. Creació d’un camp magnètic Annex V. Càlcul de la intensitat del camp magnètic amb una bobina Annex VI. Mesura del camp magnètic terrestre amb la bobina de Helmholtz Annex VII. Entrevista al Dr. Juan Marcos Fernández-Pradas Annex VIII. Entrevista al Dr. Albert Griera 5 6 Teniu a les vostres mans el treball de recerca guanyador del 17è Premi Miquel Segura, que atorga l’Ajuntament de Rubí a les millors investigacions realitzades per l’alumnat de batxillerat del municipi. Amb el pas dels anys, aquest reconeixement ha esdevingut un referent per al jovent dels nostres cen- tres educatius, que tenen en aquest premi un incentiu a l’hora de desenvolupar les seves recerques. Això es nota tant en el nombre de treballs presentats com en la qualitat del seu contingut, amb temàti- ques molt interessants i que sovint ens sorprenen. Aquest any, el treball guanyador s’ocupa del magnetisme de la Terra. La seva autora, l’Arwa Mehmood, ha fet una gran feina teòrica recopilant la història del geomagnetisme i ha completat aquesta recerca aplicant els seus coneixements al laboratori, exemplificant d’aquesta manera el gran valor d’aquest tipus de treballs. No es tracta de fer grans descobriments, sinó que l’alumnat es familiaritzi amb els mètodes de recerca i que aprengui a utilitzar-los per a la resolució de problemes. Dit d’una altra manera: que posi les bases del que serà, d’aquí a uns anys, la seva carrera professional. Vull felicitar l’autora del treball per l’esforç que hi ha dedicat, així com a la resta de joves que van pre- sentar les seves investigacions al premi. Els bons resultats obtinguts demostren el nivell assolit per l’alumnat de batxillerat i ens encoratgen a seguir apostant per una formació que combini coneixement, treball pràctic i esperit crític. Us animo a llegir aquest llibre amb atenció. Fins i tot si us sentiu uns neòfits en la matèria, de ben segur que la qualitat del treball despertarà el vostre interès i curiositat. Ana María Martínez Alcaldessa de Rubí 7 Aquesta nova convocatòria del Premi Miquel Segura presenta com a novetat l’edició del treball guanya- dor de la 17a edició en format digital; abandonant, així, l’edició en paper i adaptant l’esperit d’aquests premis als temps actuals. Com a regidor d’Educació vull valorar el treball i l’esforç dut a terme durant mesos pels alumnes i pro- fessors dels centres de secundària de la ciutat, que han elaborat els diversos treballs presentats i han donat a conèixer a la ciutadania la feina realitzada. La voluntat de la Regidoria d’Educació de l’Ajuntament de Rubí és avançar en un futur cap a la innovació d’aquests premis, introduint-hi novetats que donin resposta a les noves demandes del món educatiu i científic, incidint especialment en les demandes i expectatives de futur de la societat, els nostres joves. El treball premiat en la passada edició: El magnetisme de la Terra, de l’autora Arwa Mehmood ens situa en l’àmbit del camp magnètic de la Terra, que tot i poder-nos semblar immutable i invariable serà notícia en el futur d’acord amb els estudis internacionals fets per la Universitat de Califòrnia a Berkeley (UCB) i la Universitat de Columbia, juntament amb investigadors francesos i italians. Voldria agrair a l’Arwa Mehmood la feina feta i animar-la a continuar treballant des dels àmbits científics per millorar la societat. Gràcies pel teu temps, per la teva dedicació i pel teu treball. Sergi Garcia Roig Regidor d’Educació de l’Ajuntament de Rubí 8 PRÒLEG Aquest treball va començar amb la idea de reproduir un experiment i mesurar el camp magnètic de la Terra. Però des de bon començament van aparèixer els dubtes i el treball va prendre una altra direcció: la idea inicial, l’experiment, ha acabat sent el final del treball. La recerca històrica per descobrir com s’han desenvolupat el concepte del magnetisme i el del magnetisme a la Terra van passar a ser la part inicial del treball, així com la descoberta de com s’han anat modificant els conceptes al llarg del temps. Un treball d’història de la ciència, i sobre magnetisme, és una novetat. El desconeixement sobre el tema i el fet d’haver d’investigar per saber d’on provenien els conceptes científics han suposat dificultats afegides. Però ha valgut la pena. L’Arwa ha aconseguit un treball acurat i llegir-lo és seguir tota la his- tòria del magnetisme: des de les primeres explicacions de l’antiguitat fins les idees i propostes actuals. L’Arwa ho va voler així. Ha estat molt interessada en la part històrica i en l’esforç del pensament cientí- fic en aquest tema. I ha treballat amb molt entusiasme en l’experimentació al laboratori: ha aconseguit reproduir els experiments i ha obtingut els valors de magnetisme terrestre a Rubí. Convido a tothom a llegir aquest treball per aprendre més sobre el magnetisme de la Terra i felicito l’Arwa per la bona feina feta. Joan Arjona Fuentes Director de l' Institut JV Foix 9 10 AGRAÏMENTS Aquest treball de recerca ha estat possible gràcies a moltes persones que m’han obert la porta a un món que desconeixia, han col·laborat amb mi i m’han ofert el seu suport. Per aquest motiu, amb aques- tes línies vull donar les gràcies a tots aquells que d’una manera o una altra m’han ajudat a fer-lo. En primer lloc, m’agradaria agrair el suport i l’interès del meu tutor, Joan Arjona, que des del primer moment va animar-me a seguir endavant. Gràcies també a Juan Marcos Fernández-Pradas, que amb generositat va decidir involucrar-se en aquest treball i m’ha facilitat els mitjans necessaris per realitzar- lo, i a Albert Griera, per oferir-me la seva ajuda en l’últim moment i aconsellar-me. A la bibliotecària Isabel Filella, per facilitar-me la recerca bibliogràfica. A José Luis Ciria Pueyo, per fer possible que funcionés el meu muntatge. A Isidre Marías Benito, que em va fer llegir El nom de la rosa i El món de Sofia, lectures que m’han servit per situar-me en el context històric. I, finalment, al meu pare, per la seva paciència. 11 12 INTRODUCCIÓ El camp magnètic terrestre, els efectes del qual es van començar a observar ja fa mil·lennis, continua sent encara un dels misteris per als quals la ciència té moltes preguntes i no tantes respostes, de ma- nera que ens fa qüestionar si realment entenem com funciona el nostre planeta i el coneixem tan bé com creiem.
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