Timothy Hall,畢業於美國哥倫比亞大學,英語語言學專業碩士。
Arthur H. Milch,美國新澤西學院TESOL專業教育學碩士。
Denise McCormack,美國新澤西學院TESOL專業教育學碩士。
The principles making radio possible were developed throughout the nineteenth century. The first breakthrough was by the British physicist Michael Faraday in 1831. He discovered that when an electric current passes through one wire, it produces a current in another wire even though the wires do not touch each other. In 1864, James Maxwell showed that this current——composed of electromagnetic waves——travels at the speed of light. Heinrich Hertz proved that the waves pass through solid objects. With these discoveries in place, the race was on to develop a system of wireless radio.
Among the contenders was Reginald Fessenden, a Canadian inventor. Fessenden began experimenting with radio detectors in order to explore the possibility of voice transmission. In 1900, he was the first person to transmit his voice, but the sound was unrecognizable because the waves were not continuous. He invented a barreter detector, taking its name from the French word exchanger, to receive AM (amplitude modulated) signals, but it was not sensitive enough. One day in 1901, he accidentally left a filament of wire in acid for too long until only a tip of the wire was in contact with the acid. Fessenden noticed that, with the wire in the acid, the barreter was very sensitive to nearby continuous radio waves.
Fessenden called his invention a liquid barreter, but it became known as an electrolytic detector. The detector consisted of several connected parts forming an electric circuit. A silver-coated platinum wire was dipped into a small platinum cup filled with nitric or sulfuric acid and connected to the ground. A battery was connected between the wire and the acid, prompting a current to flow in the detector. Someone wearing headphones that were hooked up to the detector could hear a hissing noise, which could be adjusted by turning a dial until the hissing noise stopped. At that point, the detector was highly sensitive to incoming radio waves.
……
很不錯很好,還在收發室,不知道啥時候能拿到。齣差。
評分特彆有用的教輔,還是618價格公道,買全瞭
評分很不錯很好,還在收發室,不知道啥時候能拿到。齣差。
評分好評!正版書,下次需要會再來的!
評分考試 學習用書,比較有價值。
評分書非常好,備考有用。快遞小哥很棒
評分一整套書都買齊瞭,利用活動購買,所有質量很好
評分準備托福考試。需要一些有關托福方麵的資料。這就來到京東。正好趕上京東搞活動。總共買瞭十幾本有關這方麵的書。趕緊抓緊時間準備考試。
評分看著不錯呢,好好學英語。封皮兒色差好大。
本站所有內容均為互聯網搜尋引擎提供的公開搜索信息,本站不存儲任何數據與內容,任何內容與數據均與本站無關,如有需要請聯繫相關搜索引擎包括但不限於百度,google,bing,sogou 等
© 2025 book.cndgn.com All Rights Reserved. 新城书站 版權所有