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.
……
這本托福閱讀還是不錯,好好準備考試,
評分自己復習托福還可以
評分買瞭第二本,給我的同學! 我推薦給他的!
評分産品已經收到瞭質量很好
評分 評分吾消費京東商城數年,深知各産品琳琅滿目。然,唯此寶物與眾皆不同,為齣淤泥之清蓮。使吾為之動容,心馳神往,以至茶飯不思,寢食難安,輾轉反側無法忘懷。於是乎緊衣縮食,湊齊銀兩,傾吾之所有而能買。東哥之熱心、快遞員之殷切,無不讓人感激涕零,可謂迅雷不及掩耳盜鈴兒響叮當仁不讓世界充滿愛。待打開包裹之時,頓時金光四射,屋內升起七彩祥雲,處處皆是祥和之氣。吾驚訝之餘甚是欣喜若狂,嗚呼哀哉!此寶乃是天上物,人間又得幾迴求!遂沐浴更衣,焚香禱告後與人共賞此寶。人皆贊嘆不已,故生此寶物款型及做工,超高性價比之慨,且贊吾獨具慧眼與時尚品位。産品介紹果然句句實言,毫無誇大欺瞞之嫌。實乃大傢之風範,忠義之商賈。
評分京東快遞很快,很滿意的效率,求質量也不錯,挺好的購物。
評分很棒的書呢 很實用哦 推薦推薦!
評分印刷清晰,內容豐富,喜歡!
本站所有内容均为互联网搜索引擎提供的公开搜索信息,本站不存储任何数据与内容,任何内容与数据均与本站无关,如有需要请联系相关搜索引擎包括但不限于百度,google,bing,sogou 等
© 2025 book.tinynews.org All Rights Reserved. 静思书屋 版权所有