WhydidSturgeon'selectr omagnetcouldsupportninepoundsofiron?
A.Becausetheironrodwasbentintotheshapeofa“horseshoe”.
B.Becausetherodwascoatedwithvarnish.
C.Becausealayerofcopperwirewaswrappedaroundtherod.
D.Becausetherodwasmademagneticbythepassingcurrent.
正确答案:D[解析]答案见文章第3第4句。电流通过金属丝,使得金属棒带有磁性,由于磁性的吸引,金属棒可以承受9磅的铁。



