{"id":327,"date":"2019-05-14T13:33:21","date_gmt":"2019-05-14T11:33:21","guid":{"rendered":"https:\/\/www.bbemg.uliege.be\/?page_id=327"},"modified":"2026-02-11T14:47:49","modified_gmt":"2026-02-11T13:47:49","slug":"concept-de-champs","status":"publish","type":"page","link":"https:\/\/www.bbemg.uliege.be\/fr\/concept-de-champs\/","title":{"rendered":"Concept de champs"},"content":{"rendered":"[vc_row type=\u00a0\u00bbin_container\u00a0\u00bb full_screen_row_position=\u00a0\u00bbmiddle\u00a0\u00bb scene_position=\u00a0\u00bbcenter\u00a0\u00bb text_color=\u00a0\u00bbdark\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb overlay_strength=\u00a0\u00bb0.3″ shape_divider_position=\u00a0\u00bbbottom\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_link_target=\u00a0\u00bb_self\u00a0\u00bb column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb tablet_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb phone_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][heading]\n

Concept de champs<\/h1>\n[\/heading][\/vc_column][\/vc_row][vc_row type=\u00a0\u00bbin_container\u00a0\u00bb full_screen_row_position=\u00a0\u00bbmiddle\u00a0\u00bb scene_position=\u00a0\u00bbcenter\u00a0\u00bb text_color=\u00a0\u00bbdark\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb overlay_strength=\u00a0\u00bb0.3″ shape_divider_position=\u00a0\u00bbbottom\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb source=\u00a0\u00bb\u00a0\u00bb text=\u00a0\u00bb2013 – 2017″ font_container=\u00a0\u00bbtag:h2|text_align:left|color:%2349b0e5″ use_theme_fonts=\u00a0\u00bbyes\u00a0\u00bb google_fonts=\u00a0\u00bbfont_family:Abril%20Fatface%3Aregular|font_style:400%20regular%3A400%3Anormal\u00a0\u00bb css_animation=\u00a0\u00bb\u00a0\u00bb link=\u00a0\u00bb\u00a0\u00bb el_id=\u00a0\u00bb\u00a0\u00bb el_class=\u00a0\u00bb\u00a0\u00bb css=\u00a0\u00bb\u00a0\u00bb][vc_column column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_link_target=\u00a0\u00bb_self\u00a0\u00bb column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb tablet_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb phone_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_custom_heading text=\u00a0\u00bbIntroduction\u00a0\u00bb font_container=\u00a0\u00bbtag:h2|text_align:left|color:%2349b0e5″ use_theme_fonts=\u00a0\u00bbyes\u00a0\u00bb][vc_column_text]En physique, un champ est une zone de l’espace dans laquelle s’exerce une force gravitationnelle, magn\u00e9tique, \u00e9lectrostatique ou de toute autre nature (Source : Microsoft Encarta, 2009).<\/p>\n

Les champs \u00e9lectrique et magn\u00e9tique sont des concepts distincts qui ont \u00e9t\u00e9 invent\u00e9s pour expliquer les ph\u00e9nom\u00e8nes d’interaction \u00e0 distance de l’\u00e9lectricit\u00e9.<\/p>\n

En 1820, lorsque Hans Christian \u0152rsted met en \u00e9vidence que l’aiguille d’une boussole d\u00e9vie lorsqu\u2019elle est plac\u00e9e au voisinage d\u2019un fil parcouru par un courant \u00e9lectrique continu, il ouvre les portes de l’\u00e9lectromagn\u00e9tisme, cette branche de la physique qui \u00e9tudie les interactions \u00e0 distance des champs \u00e9lectrique et magn\u00e9tique.[\/vc_column_text][\/vc_column][\/vc_row][vc_row type=\u00a0\u00bbin_container\u00a0\u00bb full_screen_row_position=\u00a0\u00bbmiddle\u00a0\u00bb equal_height=\u00a0\u00bbyes\u00a0\u00bb content_placement=\u00a0\u00bbmiddle\u00a0\u00bb scene_position=\u00a0\u00bbcenter\u00a0\u00bb text_color=\u00a0\u00bbdark\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb bottom_padding=\u00a0\u00bb15″ id=\u00a0\u00bbrowCompass\u00a0\u00bb overlay_strength=\u00a0\u00bb0.3″ shape_divider_position=\u00a0\u00bbbottom\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb shape_type=\u00a0\u00bbspeech\u00a0\u00bb][vc_column column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_link_target=\u00a0\u00bb_self\u00a0\u00bb column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb tablet_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb phone_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_color=\u00a0\u00bb#262626″ column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb328″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbNone\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Sans courant dans le fil \u00e9lectrique, l’aiguille
\nrouge de la boussole indique le Nord<\/p>\n[\/vc_column_text][\/vc_column][vc_column column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_link_target=\u00a0\u00bb_self\u00a0\u00bb column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb tablet_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb phone_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_color=\u00a0\u00bb#262626″ column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb329″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbNone\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Le courant circule de droite \u00e0 gauche.
\nLa boussole en perd le Nord!<\/p>\n[\/vc_column_text][\/vc_column][\/vc_row][vc_row type=\u00a0\u00bbin_container\u00a0\u00bb full_screen_row_position=\u00a0\u00bbmiddle\u00a0\u00bb scene_position=\u00a0\u00bbcenter\u00a0\u00bb text_color=\u00a0\u00bbdark\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb overlay_strength=\u00a0\u00bb0.3″ shape_divider_position=\u00a0\u00bbbottom\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_link_target=\u00a0\u00bb_self\u00a0\u00bb column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb tablet_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb phone_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]Dans cette page, nous parlons des champs \u00e9lectrique et magn\u00e9tique. Nous entrerons ensuite dans le domaine de l’\u00e9lectromagn\u00e9tisme.[\/vc_column_text][\/vc_column][\/vc_row][vc_row type=\u00a0\u00bbin_container\u00a0\u00bb full_screen_row_position=\u00a0\u00bbmiddle\u00a0\u00bb scene_position=\u00a0\u00bbcenter\u00a0\u00bb text_color=\u00a0\u00bbdark\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb overlay_strength=\u00a0\u00bb0.3″ shape_divider_position=\u00a0\u00bbbottom\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_link_target=\u00a0\u00bb_self\u00a0\u00bb column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb tablet_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb phone_text_alignment=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][toggles style=\u00a0\u00bbdefault\u00a0\u00bb][toggle color=\u00a0\u00bbExtra-Color-2″ title=\u00a0\u00bbChamp \u00e9lectrique\u00a0\u00bb][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]Le champ \u00e9lectrique est g\u00e9n\u00e9r\u00e9 par la pr\u00e9sence des charges \u00e9lectriques. Prenons l’exemple du ballon charg\u00e9 d’\u00e9lectricit\u00e9 statique que nos lecteurs attentifs ont d\u00e9couvert dans les \u00ab\u00a0Notions d’\u00e9lectricit\u00e9\u00a0\u00bb:[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner equal_height=\u00a0\u00bbyes\u00a0\u00bb content_placement=\u00a0\u00bbmiddle\u00a0\u00bb column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb css=\u00a0\u00bb.vc_custom_1557834294323{margin: 20px !important;padding: 10px !important;border: 1px solid #262626 !important;}\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/3″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb311″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb][\/vc_column_inner][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb2\/3″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]Le ballon est charg\u00e9 n\u00e9gativement et, par influence, les charges positives du plafond se concentrent \u00e0 proximit\u00e9. Entre les deux, il y a de l’air qui est un mauvais conducteur \u00e9lectrique. Les charges restent en place.<\/p>\n

On peut sch\u00e9matiser la situation comme suit:<\/p>\n[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb334″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Le champ \u00e9lectrique est orient\u00e9, par convention, de la zone de potentiel positif, vers la zone de potentiel n\u00e9gatif.<\/p>\n[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]L’intensit\u00e9 du champ \u00e9lectrique d\u00e9pend de la diff\u00e9rence de potentiel entre les zones charg\u00e9es ainsi que de la distance qui les s\u00e9parent. Une approximation du champ \u00e9lectrique entre deux surfaces planes est donn\u00e9e par la formule suivante (si le champ est uniforme dans l’espace):[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb335″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]Il existe un champ \u00e9lectrique naturel \u00e0 la surface de la terre. Il est cr\u00e9\u00e9 par la diff\u00e9rence de potentiel entre la haute atmosph\u00e8re (l’ionosph\u00e8re, charg\u00e9e positivement) et la terre (charg\u00e9e n\u00e9gativement).<\/p>\n

Des charges \u00e9lectriques de la terre quittent en permanence le sol vers l’atmosph\u00e8re. Les milliers d’orages qui \u00e9clatent chaque jour aux quatre coins de notre plan\u00e8te assurent, via la foudre (*), le retour de ces charges vers le sol afin de maintenir un \u00e9quilibre global et permettre la vie sur la terre.[\/vc_column_text][vc_column_text css=\u00a0\u00bb.vc_custom_1557834390162{border-top-width: 1px !important;border-right-width: 1px !important;border-bottom-width: 1px !important;border-left-width: 1px !important;padding-top: 10px !important;padding-right: 10px !important;padding-bottom: 10px !important;padding-left: 10px !important;border-left-color: #262626 !important;border-left-style: initial !important;border-right-color: #262626 !important;border-right-style: initial !important;border-top-color: #262626 !important;border-top-style: initial !important;border-bottom-color: #262626 !important;border-bottom-style: initial !important;}\u00a0\u00bb](*) L’\u00e9clair est le ph\u00e9nom\u00e8ne lumineux qui accompagne la foudre. Les gaz, sur le trajet de la d\u00e9charge \u00e9lectrique sont surchauff\u00e9s et ils \u00e9mettent alors de la lumi\u00e8re. La teinte de l’\u00e9clair sera diff\u00e9rente en fonction des conditions de l’air : plus ou moins humide, pr\u00e9sence de gr\u00eale, de poussi\u00e8res.
\nLe tonnerre correspond au bruit de la dilatation explosive des masses d’air surchauff\u00e9es sur le trajet de l’\u00e9clair.[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner equal_height=\u00a0\u00bbyes\u00a0\u00bb content_placement=\u00a0\u00bbmiddle\u00a0\u00bb column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb css=\u00a0\u00bb.vc_custom_1557834515708{margin: 20px !important;padding: 10px !important;border: 1px solid #262626 !important;}\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb336″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Champ \u00e9lectrique de l’ordre
\nde 100 \u00e0 150 V\/m<\/p>\n[\/vc_column_text][\/vc_column_inner][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb337″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Champ \u00e9lectrique pouvant atteindre 15 \u00e0 20 kV\/m<\/p>\n[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]La foudre est pr\u00e9f\u00e9rentiellement attir\u00e9e par des objets \u00e9lev\u00e9s et\/ou de forme pointue car le champ \u00e9lectrique (et donc la force exerc\u00e9e sur les charges) y est alors plus intense : c\u2019est l’effet de pointe.[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][divider line_type=\u00a0\u00bbFull Width Line\u00a0\u00bb line_thickness=\u00a0\u00bb1″ divider_color=\u00a0\u00bbdefault\u00a0\u00bb][vc_custom_heading text=\u00a0\u00bbOrigine de l’effet de pointe\u00a0\u00bb font_container=\u00a0\u00bbtag:h4|text_align:left|color:%233f3f3f\u00a0\u00bb use_theme_fonts=\u00a0\u00bbyes\u00a0\u00bb][vc_column_text]Au niveau des pointes conductrices, les charges \u00e9lectriques sont concentr\u00e9es sur une plus petite surface. Les forces \u00e9lectriques y sont donc tr\u00e8s intenses. Le champ \u00e9lectrique \u00e9lev\u00e9 qui en d\u00e9coule, entra\u00eene une ionisation de l’air et rend ce dernier meilleur conducteur de l’\u00e9lectricit\u00e9.<\/p>\n

Par exemple, un objet pointu comme un paratonnerre n’attire pas la foudre au sens strict, mais il rend plus probable par temps d’orage, gr\u00e2ce \u00e0 l’effet de pointe, la formation d\u2019effluves lumineuses visibles dans l\u2019obscurit\u00e9 (ex: feux de Saint Elme \u00e0 l\u2019extr\u00e9mit\u00e9 des mats des bateaux).<\/p>\n

L’effet de pointe est \u00e0 l’origine de l’effet couronne, un terme qui d\u00e9signe la pr\u00e9sence de d\u00e9charges partielles autour des conducteurs d’une ligne a\u00e9rienne, sous certaines conditions.<\/p>\n

La pr\u00e9sence de petites saillies \u00e0 la surface des conducteurs, comme par exemple les gouttes d’eau, les flocons de neige ou encore des insectes, produisent de fortes augmentations du champ \u00e9lectrique. L’effet couronne varie donc nettement en fonction des conditions ext\u00e9rieures et atmosph\u00e9riques
\n(Source<\/em>: site du service Transport et Distribution de l’\u00e9nergie \u00e9lectrique<\/a> de l’Universit\u00e9 de Li\u00e8ge).[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][divider line_type=\u00a0\u00bbFull Width Line\u00a0\u00bb line_thickness=\u00a0\u00bb1″ divider_color=\u00a0\u00bbdefault\u00a0\u00bb][vc_custom_heading text=\u00a0\u00bbRepr\u00e9sentation du champ \u00e9lectrique\u00a0\u00bb font_container=\u00a0\u00bbtag:h4|text_align:left|color:%233f3f3f\u00a0\u00bb use_theme_fonts=\u00a0\u00bbyes\u00a0\u00bb][vc_column_text]Si nos yeux \u00e9taient capables de visualiser les champs \u00e9lectrique et magn\u00e9tique, voici ce que nous verrions en regardant une lampe de poche \u00e9teinte et un grille-pain : uniquement un champ \u00e9lectrique continu au niveau de la lampe de poche et alternatif \u00e0 50 Hz au niveau du grille-pain.[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb css=\u00a0\u00bb.vc_custom_1557834674058{margin: 20px !important;padding: 10px !important;border: 1px solid #262626 !important;}\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]\n

Champ \u00e9lectrique continu<\/p>\n[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb338″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][\/vc_column_inner][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]\n

Champ \u00e9lectrique alternatif \u00e0 50 Hz<\/p>\n[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb339″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Le champ \u00e9lectrique \u00e9tant g\u00e9n\u00e9r\u00e9 par une tension alternative, il sera lui-m\u00eame alternatif<\/p>\n[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]Les zones les plus sombres indiquent des champs d’intensit\u00e9 plus \u00e9lev\u00e9e.[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_column_text][\/vc_column_text][\/toggle][toggle color=\u00a0\u00bbExtra-Color-2″ title=\u00a0\u00bbChamp magn\u00e9tique\u00a0\u00bb][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]Il existe \u00e9galement un champ magn\u00e9tique autour de la terre. Nous le d\u00e9tectons en observant l\u2019orientation de l\u2019aiguille d\u2019une boussole. Son origine la plus probable serait les mouvements du magma en fusion dans le noyau terrestre.<\/p>\n

Le champ magn\u00e9tique terrestre joue un r\u00f4le primordial dans la protection de notre plan\u00e8te en d\u00e9viant les particules des rayonnements cosmiques et du vent solaire. Cette protection se situe dans la magn\u00e9tosph\u00e8re (couche de l’atmosph\u00e8re au-dessus de l’ionosph\u00e8re, \u00e0 plus de 1000 km de la terre). Les aurores bor\u00e9ales (au p\u00f4le nord) et australes (au p\u00f4le sud) se forment lors de la rencontre entre les particules et la magn\u00e9tosph\u00e8re.[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner equal_height=\u00a0\u00bbyes\u00a0\u00bb content_placement=\u00a0\u00bbmiddle\u00a0\u00bb column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb css=\u00a0\u00bb.vc_custom_1557838056487{margin-top: 20px !important;margin-right: 20px !important;margin-bottom: 20px !important;margin-left: 20px !important;border-top-width: 1px !important;border-right-width: 1px !important;border-bottom-width: 1px !important;border-left-width: 1px !important;padding-top: 10px !important;padding-right: 10px !important;padding-bottom: 10px !important;padding-left: 10px !important;border-left-color: #262626 !important;border-left-style: solid !important;border-right-color: #262626 !important;border-right-style: solid !important;border-top-color: #262626 !important;border-top-style: solid !important;border-bottom-color: #262626 !important;border-bottom-style: solid !important;}\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb340″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Un aimant est plac\u00e9 sous la surface.<\/p>\n

La limaille de fer s’oriente selon les lignes de champ. Par convention, les lignes de champ sortent du p\u00f4le Nord et entrent dans le p\u00f4le Sud.
\nDans un aimant, le champ magn\u00e9tique r\u00e9sulte du mouvement des \u00e9lectrons sur eux-m\u00eames (appel\u00e9 le spin des \u00e9lectrons).<\/p>\n[\/vc_column_text][\/vc_column_inner][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb341″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n

Le courant circule du haut vers le bas. Il s’agit ici d’un courant continu de 30 A.<\/p>\n

La limaille de fer s’oriente de mani\u00e8re circulaire autour du fil, selon les lignes de champ magn\u00e9tique.
\nDans un mat\u00e9riau conducteur reli\u00e9 \u00e0 une source de tension (ici continue), le champ magn\u00e9tique r\u00e9sulte du courant \u00e9lectrique, donc du d\u00e9placement des \u00e9lectrons dans les bandes de conduction (voir \u00ab\u00a0Notions d’\u00e9lectricit\u00e9\u00a0\u00bb).<\/p>\n[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]Le champ magn\u00e9tique est g\u00e9n\u00e9r\u00e9 par le d\u00e9placement des charges. Ce d\u00e9placement prend des formes diff\u00e9rentes selon les mat\u00e9riaux et leur usage:[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][divider line_type=\u00a0\u00bbFull Width Line\u00a0\u00bb line_thickness=\u00a0\u00bb1″ divider_color=\u00a0\u00bbdefault\u00a0\u00bb][vc_custom_heading text=\u00a0\u00bbLe p\u00f4le nord magn\u00e9tique – Le p\u00f4le nord g\u00e9ographique\u00a0\u00bb font_container=\u00a0\u00bbtag:h4|text_align:left|color:%233f3f3f\u00a0\u00bb use_theme_fonts=\u00a0\u00bbyes\u00a0\u00bb][vc_column_text]Le nord magn\u00e9tique est d\u00e9fini comme \u00e9tant l’endroit o\u00f9 les lignes du champ magn\u00e9tique sont perpendiculaires \u00e0 la terre. Le nord g\u00e9ographique est, quant \u00e0 lui, d\u00e9fini par l’axe de rotation de la terre. L\u2019axe du champ magn\u00e9tique n’\u00e9tant pas align\u00e9 sur l’axe de rotation de la terre, il en r\u00e9sulte que le nord g\u00e9ographique est actuellement \u00e9loign\u00e9 d’environ 1000 km du nord magn\u00e9tique.[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner equal_height=\u00a0\u00bbyes\u00a0\u00bb content_placement=\u00a0\u00bbmiddle\u00a0\u00bb column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb css=\u00a0\u00bb.vc_custom_1557838427350{margin: 20px !important;padding: 10px !important;border: 1px solid #262626 !important;}\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][image_with_animation image_url=\u00a0\u00bb342″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][\/vc_column_inner][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/2″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]\n

L’intensit\u00e9 du champ magn\u00e9tique terrestre varie entre 30 et 50 \u00b5T en fonction de l’endroit o\u00f9 on le mesure.\u00a0 Il s’agit d’un champ statique. On peut \u00e9galement mesurer \u00e0 la surface de la terre un champ naturel variable, dont une composante \u00e0 50 Hz de 10-6<\/sup> \u00b5T.<\/p>\n[\/vc_column_text][\/vc_column_inner][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]Remarque :<\/strong> Par convention, les lignes de champ magn\u00e9tique sortent du p\u00f4le nord de l’aimant et entrent dans le p\u00f4le sud.\u00a0 En se r\u00e9f\u00e9rant \u00e0 cette convention, on voit sur l’illustration ci-dessus que le p\u00f4le nord magn\u00e9tique de la Terre est en fait le p\u00f4le sud de l’aimant \u00e9quivalent ! L’aiguille de la boussole \u00e9tant un p\u00f4le nord, elle s’oriente vers le p\u00f4le sud fictif de notre super aimant, la terre.[\/vc_column_text][\/vc_column_inner][\/vc_row_inner][vc_row_inner column_margin=\u00a0\u00bbdefault\u00a0\u00bb text_align=\u00a0\u00bbleft\u00a0\u00bb][vc_column_inner column_padding=\u00a0\u00bbno-extra-padding\u00a0\u00bb column_padding_position=\u00a0\u00bball\u00a0\u00bb background_color_opacity=\u00a0\u00bb1″ background_hover_color_opacity=\u00a0\u00bb1″ column_shadow=\u00a0\u00bbnone\u00a0\u00bb column_border_radius=\u00a0\u00bbnone\u00a0\u00bb column_link_target=\u00a0\u00bb_self\u00a0\u00bb width=\u00a0\u00bb1\/1″ tablet_width_inherit=\u00a0\u00bbdefault\u00a0\u00bb column_border_width=\u00a0\u00bbnone\u00a0\u00bb column_border_style=\u00a0\u00bbsolid\u00a0\u00bb bg_image_animation=\u00a0\u00bbnone\u00a0\u00bb][vc_column_text]La direction des lignes du champ magn\u00e9tique d\u00e9pend de la configuration de la source de champ magn\u00e9tique. Prenons deux exemples:<\/p>\n

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  1. Autour d’un fil parcouru par un courant, les lignes de champ magn\u00e9tique sont circulaires.<\/li>\n<\/ol>\n[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb343″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][image_with_animation image_url=\u00a0\u00bb344″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]\n
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    1. Dans un bobinage parcouru par un courant, les lignes de champ magn\u00e9tique ressemblent \u00e0 celles autour d’un aimant.<\/li>\n<\/ol>\n[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb345″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]Le bobinage acquiert un p\u00f4le Nord du c\u00f4t\u00e9 o\u00f9 les lignes sortent et un p\u00f4le Sud du c\u00f4t\u00e9 o\u00f9 elles entrent.[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb346″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]Le champ magn\u00e9tique en un point P<\/strong> d\u00e9pend de l’intensit\u00e9 du courant et de la distance avec le conducteur.\u00a0 Il est not\u00e9 H et est exprim\u00e9 en amp\u00e8re\/m\u00e8tre (A\/m)<\/strong>.<\/p>\n

      Le sens des lignes de champ magn\u00e9tique est obtenu gr\u00e2ce \u00e0 la r\u00e8gle de la main droite : si on oriente le pouce de la main droite dans la direction du sens conventionnel du courant (du + vers le -), le sens de flexion des doigts indique la direction du champ magn\u00e9tique.<\/p>\n

      Le champ magn\u00e9tique H (en A\/m) est souvent exprim\u00e9 par l’induction magn\u00e9tique B (en tesla, T)<\/strong>. Le champ magn\u00e9tique H et l’induction magn\u00e9tique B sont reli\u00e9s, dans un mat\u00e9riau donn\u00e9, par la relation:[\/vc_column_text][image_with_animation image_url=\u00a0\u00bb347″ alignment=\u00a0\u00bbcenter\u00a0\u00bb animation=\u00a0\u00bbFade In\u00a0\u00bb border_radius=\u00a0\u00bbnone\u00a0\u00bb box_shadow=\u00a0\u00bbnone\u00a0\u00bb max_width=\u00a0\u00bb100%\u00a0\u00bb margin_bottom=\u00a0\u00bb15″][vc_column_text]La perm\u00e9abilit\u00e9 magn\u00e9tique d’un mat\u00e9riau est la facult\u00e9 que poss\u00e8de ce mat\u00e9riau \u00e0 concentrer les lignes de flux magn\u00e9tique et donc \u00e0 augmenter la valeur de l’induction magn\u00e9tique. La valeur de l’induction magn\u00e9tique d\u00e9pend donc du milieu dans laquelle elle est produite (cf.\u00a0glossaire du site<\/a> \u00e0 la rubrique \u00ab\u00a0Perm\u00e9abilit\u00e9 magn\u00e9tique\u00a0\u00bb).<\/p>\n

      La perm\u00e9abilit\u00e9 magn\u00e9tique de l’air est de 4 \u03c0 .10-7<\/sup> H\/m.[\/vc_column_text][vc_column_text css=\u00a0\u00bb.vc_custom_1557835569726{border-top-width: 1px !important;border-right-width: 1px !important;border-bottom-width: 1px !important;border-left-width: 1px !important;padding-top: 10px !important;padding-right: 10px !important;padding-bottom: 10px !important;padding-left: 10px !important;border-left-color: #262626 !important;border-left-style: initial !important;border-right-color: #262626 !important;border-right-style: initial !important;border-top-color: #262626 !important;border-top-style: initial !important;border-bottom-color: #262626 !important;border-bottom-style: initial !important;}\u00a0\u00bb]\n

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      La perm\u00e9abilit\u00e9 magn\u00e9tique d’un mat\u00e9riau (\u00b5) s’exprime par le produit de la perm\u00e9abilit\u00e9 du vide (\u00b50, exprim\u00e9e en henry\/m\u00e8tre) et de la perm\u00e9abilit\u00e9 relative (\u00b5r, sans dimension):<\/p>\n

      \u00b5=\u00b50<\/sub>. \u00b5r<\/sub><\/p>\n