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  3. The electromagnet was invented in England by William Sturgeon, who took an iron rod and bent it into the shape of a horseshoe. T

The electromagnet was invented in England by William Sturgeon, who took an iron rod and bent it into the shape of a horseshoe. T

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问题     The electromagnet was invented in England by William Sturgeon, who took an iron rod and bent it into the shape of a horseshoe. This "horseshoe" was coated with varnish (清漆) and a layer of copper wire was wrapped around it. An electric current was passed through the wire, thus making the rod magnetic. The rod was now, because of magnetic attraction, able to support nine pound of iron.
    In the US, a scientist named Joseph Henry improved on Sturgeon’s electromagnet by insulating (使绝缘) the copper wire with silk. He was able to wrap many turns of wire around an iron core without danger of circuits between the turns. His magnet could hold 2 300 pounds.
    This experiment prompted Henry to try his hand at converting magnetism into electricity. First he coiled (缠绕, 盘绕) some insulated wire around an iron bar, connecting both ends of the wire to a galvanometer (电流计). The iron bar was placed across the poles of the electromagnet. Then the coil of the electromagnet was connected to a battery. The galvanometer indicated a voltage , then dropped to zero. Henry signaled his assistant to disconnect the coil. The galvanometer showed that once again a voltage had been produced, although this time in the opposite direction. The principle of electromagnet induction (感应现象) had thus been discovered. Unfortunately for Joseph Henry he did not publish findings and someone else (Faraday) got the credit for the discovery.
Henry’s electromagnet was______.
选项 A、exactly like Sturgeon’s
B、an improvement over Sturgeon’s
C、more dangerous than Sturgeon’s
D、not as good as Sturgeon’s
答案B
解析 本题是一道具体细节题。问亨利的电磁铁与斯特杰恩的电磁铁有什么区别。文章第二段指出，在美国，一位名叫约瑟夫·亨利的科学家改进了斯特杰恩的电磁铁，他用丝绸将铜导线进行绝缘处理。这样他便能够在铁芯上缠绕许多圈导线，而不会在线圈的匝间造成短路的危险。他的电磁铁可以吸起2 300磅的铁。因此，本题的正确答案应是B“亨利的电磁铁是斯特杰恩的电磁铁的改进”。
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