Номер 618, страница 85, часть 1 - гдз по физике 10-11 класс сборник задач Парфентьева

Авторы: Парфентьева Н. А.

Тип: Сборник задач

Серия: классический курс

Издательство: Просвещение

Год издания: 2007 - 2026

Часть: 1

Цвет обложки: фиолетовый

ISBN: 978-5-09-092936-3

Часть 1. 10 класс. Основы электродинамики. Электростатика. Электроёмкость. Энергия электрического поля конденсатора - номер 618, страница 85.

App\Models\Task {#1030 // resources/views/models/task/default.blade.php
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                    "field_default_folder" => "/fizika_10/parfenteva-sz/"
                    "field_isbn" => "978-5-09-092936-3"
                    "field_cover" => array:1 [ …1]
                    "field_cover_alts" => array:1 [ …1]
                    "field_covers" => array:1 [ …1]
                    "field_popular_book" => "0"
                    "field_recommended_books" => Illuminate\Database\Eloquent\Collection {#1104 …2}
                    "field_new_book" => Illuminate\Database\Eloquent\Collection {#1105 …2}
                    "field_old_book" => Illuminate\Database\Eloquent\Collection {#1106 …2}
                    "field_url" => "/10-klass/fizika/parfenteva-sbornik-zadach"
                    "field_cover_color" => Illuminate\Database\Eloquent\Collection {#1107 …2}
                    "field_metatags_title" => null
                    "field_metatags_description" => null
                    "field_h1" => null
                    "field_description_top" => null
                    "field_description_bottom" => null
                    "breadcrumbs" => array:3 [ …3]
                  ]
                  #changes: []
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                  #attributeCastCache: []
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                  #dispatchesEvents: []
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                  #touches: []
                  +timestamps: true
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                  #hidden: []
                  #visible: []
                  #fillable: []
                  #guarded: array:1 [
                    0 => "*"
                  ]
                }
              ]
              #escapeWhenCastingToString: false
            }
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1109
              #items: []
              #escapeWhenCastingToString: false
            }
          ]
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            "id" => 1319883
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "field_display_title" => null
            "field_branch_order" => "1"
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1076}
            "field_page_start" => "5"
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            "field_h1" => null
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            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1077}
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            0 => "*"
          ]
        }
        1 => App\Models\Branch {#1110
          #connection: "mysql"
          #table: "branches"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
          +preventsLazyLoading: false
          #perPage: 15
          +exists: true
          +wasRecentlyCreated: false
          #escapeWhenCastingToString: false
          #attributes: array:24 [
            "id" => 1319884
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "field_display_title" => "10 класс"
            "field_branch_order" => null
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1111
              #items: []
              #escapeWhenCastingToString: false
            }
            "field_page_start" => "5"
            "field_branch_display" => "0"
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            "field_display_branch_in_title" => "1"
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            "field_h1" => null
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            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1112
              #items: array:1 [
                0 => App\Models\Book {#1113
                  #connection: "mysql"
                  #table: "books"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
                  +wasRecentlyCreated: false
                  #escapeWhenCastingToString: false
                  #attributes: array:50 [
                    "id" => 3751
                    "created_at" => "2026-04-10 13:58:26"
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                    "field_subject" => Illuminate\Database\Eloquent\Collection {#1114 …2}
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                    "field_publisher" => Illuminate\Database\Eloquent\Collection {#1119 …2}
                    "field_author" => Illuminate\Database\Eloquent\Collection {#1121 …2}
                    "field_author_foreign" => Illuminate\Database\Eloquent\Collection {#1123 …2}
                    "field_book_type" => Illuminate\Database\Eloquent\Collection {#1124 …2}
                    "field_country" => Illuminate\Database\Eloquent\Collection {#1126 …2}
                    "field_city" => Illuminate\Database\Eloquent\Collection {#1128 …2}
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                    "field_level_of_education" => Illuminate\Database\Eloquent\Collection {#1133 …2}
                    "field_standart_of_education" => Illuminate\Database\Eloquent\Collection {#1134 …2}
                    "field_publication_number" => "13"
                    "field_publication_type" => Illuminate\Database\Eloquent\Collection {#1136 …2}
                    "field_under_the_edition" => Illuminate\Database\Eloquent\Collection {#1138 …2}
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                    "field_cover_description" => null
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                    "field_for_whom" => "Учебное пособие"
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                    "field_tasks_count" => "1110"
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                    "field_default_folder" => "/fizika_10/parfenteva-sz/"
                    "field_isbn" => "978-5-09-092936-3"
                    "field_cover" => array:1 [ …1]
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                    "field_cover_color" => Illuminate\Database\Eloquent\Collection {#1142 …2}
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                    "breadcrumbs" => array:3 [ …3]
                  ]
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                    "field_author" => Illuminate\Database\Eloquent\Collection {#1121 …2}
                    "field_author_foreign" => Illuminate\Database\Eloquent\Collection {#1123 …2}
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                    "field_publication_number" => "13"
                    "field_publication_type" => Illuminate\Database\Eloquent\Collection {#1136 …2}
                    "field_under_the_edition" => Illuminate\Database\Eloquent\Collection {#1138 …2}
                    "field_under_the_edition_degree" => null
                    "field_cover_description" => null
                    "field_publication_year" => "2007"
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                    "field_cover" => array:1 [ …1]
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                    "breadcrumbs" => array:3 [ …3]
                  ]
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              ]
              #escapeWhenCastingToString: false
            }
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1144
              #items: array:1 [
                0 => App\Models\Branch {#1145
                  #connection: "mysql"
                  #table: "branches"
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                  #keyType: "int"
                  +incrementing: true
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                  #escapeWhenCastingToString: false
                  #attributes: array:24 [
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                    "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1146 …2}
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                    "book" => Illuminate\Database\Eloquent\Collection {#1148 …2}
                    "branch_parent" => Illuminate\Database\Eloquent\Collection {#1149 …2}
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                    "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1146 …2}
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                    "book" => Illuminate\Database\Eloquent\Collection {#1148 …2}
                    "branch_parent" => Illuminate\Database\Eloquent\Collection {#1149 …2}
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                  ]
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              ]
              #escapeWhenCastingToString: false
            }
          ]
          #original: array:24 [
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            "created_at" => "2026-04-10 13:58:26"
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            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1111}
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            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1112}
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          ]
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            0 => "*"
          ]
        }
        2 => App\Models\Branch {#1150
          #connection: "mysql"
          #table: "branches"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
          #withCount: []
          +preventsLazyLoading: false
          #perPage: 15
          +exists: true
          +wasRecentlyCreated: false
          #escapeWhenCastingToString: false
          #attributes: array:24 [
            "id" => 1319940
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
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            "field_branch_order" => null
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1151
              #items: []
              #escapeWhenCastingToString: false
            }
            "field_page_start" => "72"
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            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1152
              #items: array:1 [
                0 => App\Models\Book {#1153
                  #connection: "mysql"
                  #table: "books"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
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                  #escapeWhenCastingToString: false
                  #attributes: array:50 [
                    "id" => 3751
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                    "field_author" => Illuminate\Database\Eloquent\Collection {#1161 …2}
                    "field_author_foreign" => Illuminate\Database\Eloquent\Collection {#1163 …2}
                    "field_book_type" => Illuminate\Database\Eloquent\Collection {#1164 …2}
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                    "field_city" => Illuminate\Database\Eloquent\Collection {#1168 …2}
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                    "field_level_of_education" => Illuminate\Database\Eloquent\Collection {#1173 …2}
                    "field_standart_of_education" => Illuminate\Database\Eloquent\Collection {#1174 …2}
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                    "field_publication_type" => Illuminate\Database\Eloquent\Collection {#1176 …2}
                    "field_under_the_edition" => Illuminate\Database\Eloquent\Collection {#1178 …2}
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                    "field_cover_description" => null
                    "field_publication_year" => "2007"
                    "field_publication_year_until" => null
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                    "field_link_to_source" => null
                    "field_tasks_count" => "1110"
                    "field_priority" => null
                    "field_default_folder" => "/fizika_10/parfenteva-sz/"
                    "field_isbn" => "978-5-09-092936-3"
                    "field_cover" => array:1 [ …1]
                    "field_cover_alts" => array:1 [ …1]
                    "field_covers" => array:1 [ …1]
                    "field_popular_book" => "0"
                    "field_recommended_books" => Illuminate\Database\Eloquent\Collection {#1179 …2}
                    "field_new_book" => Illuminate\Database\Eloquent\Collection {#1180 …2}
                    "field_old_book" => Illuminate\Database\Eloquent\Collection {#1181 …2}
                    "field_url" => "/10-klass/fizika/parfenteva-sbornik-zadach"
                    "field_cover_color" => Illuminate\Database\Eloquent\Collection {#1182 …2}
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                    "field_metatags_description" => null
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                    "breadcrumbs" => array:3 [ …3]
                  ]
                  #original: array:50 [
                    "id" => 3751
                    "created_at" => "2026-04-10 13:58:26"
                    "updated_at" => null
                    "field_tree_default_status" => "tasks"
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                     …45
                  ]
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              ]
              #escapeWhenCastingToString: false
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            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1184
              #items: array:1 [
                0 => App\Models\Branch {#1185
                  #connection: "mysql"
                  #table: "branches"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: true
                  #with: []
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                  #attributes: array:24 [ …24]
                  #original: array:24 [ …24]
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                }
              ]
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            "field_branch_cover" => []
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            "book" => Illuminate\Database\Eloquent\Collection {#1152}
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1184}
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        }
        3 => App\Models\Branch {#1225
          #connection: "mysql"
          #table: "branches"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
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            "created_at" => "2026-04-10 13:58:26"
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            "field_branch_order" => null
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1226
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            "field_page_start" => "72"
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            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1227
              #items: array:1 [
                0 => App\Models\Book {#1228
                  #connection: "mysql"
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                }
              ]
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            }
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1259
              #items: array:1 [
                0 => App\Models\Branch {#1260
                  #connection: "mysql"
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                  #escapeWhenCastingToString: false
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                }
              ]
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            "field_display_title" => "Электростатика"
            "field_branch_order" => null
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1226}
            "field_page_start" => "72"
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            "field_display_branch_in_title" => "1"
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            "field_display_branch_page" => "1"
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            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1227}
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1259}
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        4 => App\Models\Branch {#1304
          #connection: "mysql"
          #table: "branches"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
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          #escapeWhenCastingToString: false
          #attributes: array:24 [
            "id" => 1319946
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "field_display_title" => "Электроёмкость. Энергия электрического поля конденсатора"
            "field_branch_order" => null
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1305
              #items: []
              #escapeWhenCastingToString: false
            }
            "field_page_start" => "83"
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            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1306
              #items: array:1 [
                0 => App\Models\Book {#1307
                  #connection: "mysql"
                  #table: "books"
                  #primaryKey: "id"
                  #keyType: "int"
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                  +preventsLazyLoading: false
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                  #escapeWhenCastingToString: false
                  #attributes: array:50 [ …50]
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              ]
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            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1338
              #items: array:1 [
                0 => App\Models\Branch {#1339
                  #connection: "mysql"
                  #table: "branches"
                  #primaryKey: "id"
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                  +incrementing: true
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                  #attributes: array:24 [ …24]
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          #original: array:24 [
            "id" => 1319946
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "field_display_title" => "Электроёмкость. Энергия электрического поля конденсатора"
            "field_branch_order" => null
            "field_url" => null
            "field_branch_type" => Illuminate\Database\Eloquent\Collection {#1305}
            "field_page_start" => "83"
            "field_branch_display" => "0"
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            "field_display_branch_in_title" => "1"
            "field_display_task_interval" => "0"
            "field_display_branch_page" => "1"
            "field_branch_title_in_content" => "0"
            "field_navigation_title" => null
            "field_metatags_title" => null
            "field_metatags_description" => null
            "field_h1" => null
            "field_description_top" => null
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            "field_branch_cover" => []
            "field_branch_covers" => []
            "book" => Illuminate\Database\Eloquent\Collection {#1306}
            "branch_parent" => Illuminate\Database\Eloquent\Collection {#1338}
          ]
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    "content" => Illuminate\Database\Eloquent\Collection {#1387
      #items: array:2 [
        0 => App\Models\Element {#1398
          #connection: "mysql"
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          #attributes: array:7 [
            "id" => 1496779
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1407
              #items: array:1 [
                0 => App\Models\Edition {#1399
                  #connection: "mysql"
                  #table: "editions"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
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                  +preventsLazyLoading: false
                  #perPage: 15
                  +exists: true
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                  #escapeWhenCastingToString: false
                  #attributes: array:21 [ …21]
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            "task" => array:2 [
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              "type" => "task"
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            "text" => "<p><strong>618. H</strong> Энергия плоского воздушного конденсатора $W_1 = 2 \cdot 10^{-7}$ Дж. Определите энергию конденсатора после заполнения его диэлектриком с диэлектрической проницаемостью $\varepsilon = 2$, если:</p><p><strong>a)</strong> конденсатор отключён от источника питания;</p><p><strong>б)</strong> конденсатор подключён к источнику питания.</p>"
            "img" => array:1 [
              0 => array:5 [
                "name" => "618-1.jpg"
                "alt" => null
                "width" => "1379"
                "height" => 385
                "path" => "/media/fizika_10/parfenteva-sz/0-1/618-1.webp?ts=1756373454"
              ]
            ]
          ]
          #original: array:7 [
            "id" => 1496779
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1407}
            "task" => array:2 [
              "refs" => "1320621"
              "type" => "task"
            ]
            "text" => "<p><strong>618. H</strong> Энергия плоского воздушного конденсатора $W_1 = 2 \cdot 10^{-7}$ Дж. Определите энергию конденсатора после заполнения его диэлектриком с диэлектрической проницаемостью $\varepsilon = 2$, если:</p><p><strong>a)</strong> конденсатор отключён от источника питания;</p><p><strong>б)</strong> конденсатор подключён к источнику питания.</p>"
            "img" => array:1 [
              0 => array:5 [
                "name" => "618-1.jpg"
                "alt" => null
                "width" => "1379"
                "height" => 385
                "path" => "/media/fizika_10/parfenteva-sz/0-1/618-1.webp?ts=1756373454"
              ]
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          ]
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          #hidden: []
          #visible: []
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          #guarded: array:1 [
            0 => "*"
          ]
        }
        1 => App\Models\Element {#1405
          #connection: "mysql"
          #table: "elements"
          #primaryKey: "id"
          #keyType: "int"
          +incrementing: true
          #with: []
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          +exists: true
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          #escapeWhenCastingToString: false
          #attributes: array:6 [
            "id" => 1724706
            "created_at" => "2026-04-10 13:58:26"
            "updated_at" => null
            "edition" => Illuminate\Database\Eloquent\Collection {#1415
              #items: array:1 [
                0 => App\Models\Edition {#1406
                  #connection: "mysql"
                  #table: "editions"
                  #primaryKey: "id"
                  #keyType: "int"
                  +incrementing: false
                  #with: []
                  #withCount: []
                  +preventsLazyLoading: false
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                  #attributes: array:21 [ …21]
                  #original: array:21 [ …21]
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                  #guarded: array:1 [ …1]
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            "task" => array:2 [
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              "type" => "task"
            ]
            "text" => "<p><strong>Дано:</strong></p><p>Энергия воздушного конденсатора, $W_1 = 2 \cdot 10^{-7}$ Дж</p><p>Диэлектрическая проницаемость диэлектрика, $\epsilon = 2$</p><p>Все данные представлены в системе СИ.</p><p><strong>Найти:</strong></p><p>$W_{2a}$ — энергия конденсатора с диэлектриком, отключённого от источника.</p><p>$W_{2b}$ — энергия конденсатора с диэлектриком, подключённого к источнику.</p><p><strong>Решение:</strong></p><p>Ёмкость плоского воздушного конденсатора обозначается как $C_1$. После заполнения конденсатора диэлектриком его ёмкость становится $C_2$. Связь между начальной и конечной ёмкостью выражается формулой:</p><p>$C_2 = \epsilon C_1$</p><p>Рассмотрим два случая.</p><p><strong>а) конденсатор отключён от источника питания</strong></p><p>Когда конденсатор отключают от источника питания, заряд $\text{q}$ на его обкладках остаётся постоянным ($q = \text{const}$). Энергию конденсатора в этом случае удобно выразить через заряд и ёмкость:</p><p>$W = \frac{q^2}{2C}$</p><p>Начальная энергия: $W_1 = \frac{q^2}{2C_1}$.</p><p>Конечная энергия: $W_{2a} = \frac{q^2}{2C_2}$.</p><p>Чтобы найти конечную энергию, выразим её через начальную. Для этого найдём отношение $W_{2a}$ к $W_1$:</p><p>$\frac{W_{2a}}{W_1} = \frac{q^2 / (2C_2)}{q^2 / (2C_1)} = \frac{C_1}{C_2}$</p><p>Подставим соотношение ёмкостей $C_2 = \epsilon C_1$:</p><p>$\frac{W_{2a}}{W_1} = \frac{C_1}{\epsilon C_1} = \frac{1}{\epsilon}$</p><p>Отсюда, конечная энергия равна:</p><p>$W_{2a} = \frac{W_1}{\epsilon}$</p><p>Подставим числовые значения:</p><p>$W_{2a} = \frac{2 \cdot 10^{-7}}{2} = 1 \cdot 10^{-7}$ Дж.</p><p><strong>Ответ:</strong> энергия конденсатора уменьшится в 2 раза и станет равной $1 \cdot 10^{-7}$ Дж.</p><p><strong>б) конденсатор подключён к источнику питания</strong></p><p>Когда конденсатор остаётся подключённым к источнику питания, напряжение $\text{U}$ на его обкладках остаётся постоянным ($U = \text{const}$). Энергию конденсатора в этом случае удобно выразить через ёмкость и напряжение:</p><p>$W = \frac{CU^2}{2}$</p><p>Начальная энергия: $W_1 = \frac{C_1 U^2}{2}$.</p><p>Конечная энергия: $W_{2b} = \frac{C_2 U^2}{2}$.</p><p>Найдём отношение $W_{2b}$ к $W_1$:</p><p>$\frac{W_{2b}}{W_1} = \frac{C_2 U^2 / 2}{C_1 U^2 / 2} = \frac{C_2}{C_1}$</p><p>Подставим соотношение ёмкостей $C_2 = \epsilon C_1$:</p><p>$\frac{W_{2b}}{W_1} = \frac{\epsilon C_1}{C_1} = \epsilon$</p><p>Отсюда, конечная энергия равна:</p><p>$W_{2b} = \epsilon W_1$</p><p>Подставим числовые значения:</p><p>$W_{2b} = 2 \cdot (2 \cdot 10^{-7}) = 4 \cdot 10^{-7}$ Дж.</p><p><strong>Ответ:</strong> энергия конденсатора увеличится в 2 раза и станет равной $4 \cdot 10^{-7}$ Дж.</p>"
          ]
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            "edition" => Illuminate\Database\Eloquent\Collection {#1415}
            "task" => array:2 [
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            "text" => "<p><strong>Дано:</strong></p><p>Энергия воздушного конденсатора, $W_1 = 2 \cdot 10^{-7}$ Дж</p><p>Диэлектрическая проницаемость диэлектрика, $\epsilon = 2$</p><p>Все данные представлены в системе СИ.</p><p><strong>Найти:</strong></p><p>$W_{2a}$ — энергия конденсатора с диэлектриком, отключённого от источника.</p><p>$W_{2b}$ — энергия конденсатора с диэлектриком, подключённого к источнику.</p><p><strong>Решение:</strong></p><p>Ёмкость плоского воздушного конденсатора обозначается как $C_1$. После заполнения конденсатора диэлектриком его ёмкость становится $C_2$. Связь между начальной и конечной ёмкостью выражается формулой:</p><p>$C_2 = \epsilon C_1$</p><p>Рассмотрим два случая.</p><p><strong>а) конденсатор отключён от источника питания</strong></p><p>Когда конденсатор отключают от источника питания, заряд $\text{q}$ на его обкладках остаётся постоянным ($q = \text{const}$). Энергию конденсатора в этом случае удобно выразить через заряд и ёмкость:</p><p>$W = \frac{q^2}{2C}$</p><p>Начальная энергия: $W_1 = \frac{q^2}{2C_1}$.</p><p>Конечная энергия: $W_{2a} = \frac{q^2}{2C_2}$.</p><p>Чтобы найти конечную энергию, выразим её через начальную. Для этого найдём отношение $W_{2a}$ к $W_1$:</p><p>$\frac{W_{2a}}{W_1} = \frac{q^2 / (2C_2)}{q^2 / (2C_1)} = \frac{C_1}{C_2}$</p><p>Подставим соотношение ёмкостей $C_2 = \epsilon C_1$:</p><p>$\frac{W_{2a}}{W_1} = \frac{C_1}{\epsilon C_1} = \frac{1}{\epsilon}$</p><p>Отсюда, конечная энергия равна:</p><p>$W_{2a} = \frac{W_1}{\epsilon}$</p><p>Подставим числовые значения:</p><p>$W_{2a} = \frac{2 \cdot 10^{-7}}{2} = 1 \cdot 10^{-7}$ Дж.</p><p><strong>Ответ:</strong> энергия конденсатора уменьшится в 2 раза и станет равной $1 \cdot 10^{-7}$ Дж.</p><p><strong>б) конденсатор подключён к источнику питания</strong></p><p>Когда конденсатор остаётся подключённым к источнику питания, напряжение $\text{U}$ на его обкладках остаётся постоянным ($U = \text{const}$). Энергию конденсатора в этом случае удобно выразить через ёмкость и напряжение:</p><p>$W = \frac{CU^2}{2}$</p><p>Начальная энергия: $W_1 = \frac{C_1 U^2}{2}$.</p><p>Конечная энергия: $W_{2b} = \frac{C_2 U^2}{2}$.</p><p>Найдём отношение $W_{2b}$ к $W_1$:</p><p>$\frac{W_{2b}}{W_1} = \frac{C_2 U^2 / 2}{C_1 U^2 / 2} = \frac{C_2}{C_1}$</p><p>Подставим соотношение ёмкостей $C_2 = \epsilon C_1$:</p><p>$\frac{W_{2b}}{W_1} = \frac{\epsilon C_1}{C_1} = \epsilon$</p><p>Отсюда, конечная энергия равна:</p><p>$W_{2b} = \epsilon W_1$</p><p>Подставим числовые значения:</p><p>$W_{2b} = 2 \cdot (2 \cdot 10^{-7}) = 4 \cdot 10^{-7}$ Дж.</p><p><strong>Ответ:</strong> энергия конденсатора увеличится в 2 раза и станет равной $4 \cdot 10^{-7}$ Дж.</p>"
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№618 (с. 85)
Условие. №618 (с. 85)
скриншот условия
Физика, 10-11 класс Сборник задач, автор: Парфентьева Наталия Андреевна, издательство Просвещение, Москва, 2007, Часть 1, страница 85, номер 618, Условие

618. H Энергия плоского воздушного конденсатора $W_1 = 2 \cdot 10^{-7}$ Дж. Определите энергию конденсатора после заполнения его диэлектриком с диэлектрической проницаемостью $\varepsilon = 2$, если:

a) конденсатор отключён от источника питания;

б) конденсатор подключён к источнику питания.

Решение. №618 (с. 85)

Дано:

Энергия воздушного конденсатора, $W_1 = 2 \cdot 10^{-7}$ Дж

Диэлектрическая проницаемость диэлектрика, $\epsilon = 2$

Все данные представлены в системе СИ.

Найти:

$W_{2a}$ — энергия конденсатора с диэлектриком, отключённого от источника.

$W_{2b}$ — энергия конденсатора с диэлектриком, подключённого к источнику.

Решение:

Ёмкость плоского воздушного конденсатора обозначается как $C_1$. После заполнения конденсатора диэлектриком его ёмкость становится $C_2$. Связь между начальной и конечной ёмкостью выражается формулой:

$C_2 = \epsilon C_1$

Рассмотрим два случая.

а) конденсатор отключён от источника питания

Когда конденсатор отключают от источника питания, заряд $\text{q}$ на его обкладках остаётся постоянным ($q = \text{const}$). Энергию конденсатора в этом случае удобно выразить через заряд и ёмкость:

$W = \frac{q^2}{2C}$

Начальная энергия: $W_1 = \frac{q^2}{2C_1}$.

Конечная энергия: $W_{2a} = \frac{q^2}{2C_2}$.

Чтобы найти конечную энергию, выразим её через начальную. Для этого найдём отношение $W_{2a}$ к $W_1$:

$\frac{W_{2a}}{W_1} = \frac{q^2 / (2C_2)}{q^2 / (2C_1)} = \frac{C_1}{C_2}$

Подставим соотношение ёмкостей $C_2 = \epsilon C_1$:

$\frac{W_{2a}}{W_1} = \frac{C_1}{\epsilon C_1} = \frac{1}{\epsilon}$

Отсюда, конечная энергия равна:

$W_{2a} = \frac{W_1}{\epsilon}$

Подставим числовые значения:

$W_{2a} = \frac{2 \cdot 10^{-7}}{2} = 1 \cdot 10^{-7}$ Дж.

Ответ: энергия конденсатора уменьшится в 2 раза и станет равной $1 \cdot 10^{-7}$ Дж.

б) конденсатор подключён к источнику питания

Когда конденсатор остаётся подключённым к источнику питания, напряжение $\text{U}$ на его обкладках остаётся постоянным ($U = \text{const}$). Энергию конденсатора в этом случае удобно выразить через ёмкость и напряжение:

$W = \frac{CU^2}{2}$

Начальная энергия: $W_1 = \frac{C_1 U^2}{2}$.

Конечная энергия: $W_{2b} = \frac{C_2 U^2}{2}$.

Найдём отношение $W_{2b}$ к $W_1$:

$\frac{W_{2b}}{W_1} = \frac{C_2 U^2 / 2}{C_1 U^2 / 2} = \frac{C_2}{C_1}$

Подставим соотношение ёмкостей $C_2 = \epsilon C_1$:

$\frac{W_{2b}}{W_1} = \frac{\epsilon C_1}{C_1} = \epsilon$

Отсюда, конечная энергия равна:

$W_{2b} = \epsilon W_1$

Подставим числовые значения:

$W_{2b} = 2 \cdot (2 \cdot 10^{-7}) = 4 \cdot 10^{-7}$ Дж.

Ответ: энергия конденсатора увеличится в 2 раза и станет равной $4 \cdot 10^{-7}$ Дж.

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