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Chapitre 2 : Intensité I et tension U

intensite-tension

Salutation à tous! 😀

Dans ce chapitre, nous allons voir la notion d’intensité et de tension avec les éléments de base pour schématiser un circuit électrique. Pour rappel, nous savons que le courant électrique est un mouvement d’électrons dans la matière. Ce mouvement est créé par un champ magnétique ou électrique. La science a nommé ce flux d’électrons le courant électrique, marqué I, et l’a associé avec la tension, marquée U, qui représente la force de création de ce courant. Ces deux notions sont intimement liées. Mais avant toute chose, je dois vous présenter votre premier composant électronique : le dipôle.

 

Le dipôle

Le dipôle est une représentation schématique d’un composant électronique.

dipole

Ce symbole est généralement associé aux informations suivantes:

  • son nom : “D” pour dipôle (originale 🙂 )
  • son intensité : “I”
  • sa tension : “U”
  • ces deux pattes de connexion : “+” et “-“

Les signes “+” et “-” sur les pattes ne sont pas toujours indiquées, tout simplement par convention. Au début de l’électricité, il a été décidé que le courant “I” circulait du “+” vers le “-“. Cette règle a permis à des générations d’électriciens de se comprendre entre eux. Le point amusant est, que cette convention est fausse… En effet, le fameux courant d’électrons qui compose le courant “I” circule du “-” vers le “+”. Le temps que l’on s’en rende compte, c’était déjà trop tard ! Puis, comme cela ne change rien aux calculs, il a donc été décidé de laisser les choses ainsi.

Le dipôle est donc traversé par une intensité “I” qui va de son “+” vers son “-“. Il possède aussi une tension “U”, représentée par une flèche, orientée dans le sens inverse du courant. Commençons par l’intensité…

Intensité I

L’intensité, c’est tout simplement le nombre de charges qui traverse une section par unité de temps. Ou plus simplement, le nombre d’électrons qui passe dans mon composant par secondes. Le nombre de charge est exprimé en Coulomb, noté “C”. Un coulomb vaut 6.24×1018 charges élémentaires “e” (soit 6.24×1018 électrons). La charge d’un électron étant très faible il a été décidé de les rassembler par paquet pour les calculs. C’est plus commode 🙂 . La section représente une coupe transversale du matériaux traversé. Traduit en formule cela revient à faire une dérivé.

courant i

Le courant I a pour unité l’ampère, noté A. Voyons maintenant la tension U…

 

Tension U

La tension U est une différence de potentiel entre deux points exprimée en volts. C’est une notion complexe et très abstraite. La tension représente la circulation des champs électriques dans un fil. Je ne vous en dirais pas plus car cela n’apporte rien au cours 😉 . Toutefois, vous pouvez retenir les points suivants :

  • une tension est toujours représentée du “-” vers le “+”
  • une tension est une différence de potentiel entre le “+” et le “-“. Si le “-” est à 10 et le “+” à 11, nous avons une tension de 1 volt, pas de 11 volts.

Pour faciliter les calcules avec les tensions nous avons définit un potentiel à zéro. Ce potentiel nul est représenté sur le schéma par la masse…

La masse

Dans tous circuits électriques, il faut définir un potentiel à zéro. Cela sert de point de référence à toutes les tensions du circuit. Cette masse, c’est comme le niveau de la mer pour calculer les altitudes. La mer c’est le zéro pour calculer la hauteur des montagnes. La masse c’est le zéro pour calculer les tensions. Dans la réalité, cette masse, c’est la connexion à la terre. Le potentiel de la terre, c’est le zéro international de l’électricité. C’est cette petite chose qui permet à EDF de fonctionner. Vous leur enlevez et c’est fini : plus d’électricité à la maison 😕 .

Nous avons le dipôle et la masse. Il reste à voir le dernier et le plus important des composants basiques : le générateur.

 

Le générateur

Le générateur sert à produire le courant qui circule dans les dipôles. Son symbole est un cercle coupé d’un trait. Il possède tous les attributs d’un dipôle classique. Mais son courant I est orienté dans le même sens que sa tension U.

générateurRassurez-vous le courant circule toujours du “+” vers le “-“. Sauf que c’est un générateur. Le courant par du “+” traverse les dipôles puis revient vers le “-” par l’autre coté.

 

schema

Nous voila a la fin de ce chapitre, nous avons défini le courant et la tension ainsi que les composants de base d’un schéma électrique. La prochaine fois, nous nous intéresserons aux lois qui régissent ce schéma. N’hésitez pas à poser des questions ou à faire des remarques dans les commentaires. A très bientôt!!! 😀

 

Introduction

Chapitre 1: Charge et circulation de charges

Partagez et suivez nous

27 commentaires sur Chapitre 2 : Intensité I et tension U

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