2. 外语
  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.
The galvanometer indicated______.
选项 A、that Henry’s assistant had connected the wire
B、that Henry had been able to produce a voltage
C、zero constantly
D、the iron bar had been placed across the poles of the electromagnet
答案B
解析 本题是一道具体细节题。问电流计指示了什么。利用查阅式阅读法，文章第三段后半部分指出，亨利着手搞起了磁、电转换实验。他先将一些绝缘导线绕在一根铁条上，并将导线的两端与一个电流计连接起来。这根铁条被放在电磁铁的两个极上，然后将电磁铁的线圈接通电源。这时，电流计指示出一个电压，然后，指针又回到了零。亨利示意他的助手将线圈断开连接，此时，电流计上又一次指示出一个电压，但这次的电压是反向的。因此，本题的正确答案应是B“电流计指示线路中产生了电压”。
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