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  3. The electromagnet was invented in England by William Sturgeon, who took an i

The electromagnet was invented in England by William Sturgeon, who took an i

游客2025-03-19  19
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. [br] Henry was encouraged by his experiment______.
选项 A、to insulate the copper wire
B、to change magnetism into electricity
C、to convert electricity into magnetism
D、to avoid short circuits
答案 B
解析 本题问亨利受改进试验的鼓励，打算做什么试验。文章第三段第一句话指出，这一实验促使亨利着手搞起了磁、电转换实验。因此，本题的正确答案应是B“将磁转换成电”。
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