آیا برق تلفن همان برق شهر است ؟

متن کامل
برق تلفن مستقل از برق شهر بوده و ربطی به آن ندارد. برای همین است که در زمان خاموشی تلفن کار می کند. برق تلفن از نوع مستقیم بوده اما برق شهر از نوع متناوب است. برق شهر 220 ولت و در مصارف خانگی 15 تا 25 آمپر می باشد.
 
اما برق تلفن بستگی به منطقه مورد استفاده بین 45 تا 65 ولت بوده وجریان بسیار کمی دارد، در نتیجه نه آدم را می گیرد و نه لامپی را روشن می کند. ولتاژ تلفن در حال تابت حدود 45 تا 65 ولت مستقیم است، اما وقتی تلفن زنگ می زند، یک ولتاژ متناوب قوی در حدود 100 ولت با فرکانس 25 هرتز به آن می رسد که زنگ تلفن را به صدا در می آورد. زمانی که که گوشی را بر می دارید، ولتاژ متناوب قطع و ولتاژ مستقیم تلفن به حدود 12 ولت تنزل می یابد. این ولتاژ مدار داخل تلفن را به کار انداخته، باعث می شود مکالمه از طریق گوشی و دهنی برقرار شود. حال اگر در حین مکالمه، در محل دیگر شخص دومی گوشی را بردارد، ولتاژ از این هم کمتر شده و صدا ضعیف تر خواهد شد.
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