题干

小聪将漆包线(表面涂有绝缘漆的铜线)绕在两个完全相同的铁钉上,制成了简易电磁铁甲和乙,按图连接好电路,探究“影响电磁铁磁性强弱的因素”.请你结合实验中的具体情况,完成下面的内容.

 (1)通过观察电磁铁____ 的不同,可以判断电磁铁的磁性强弱不同;

 (2)电磁铁乙的铁钉帽端为____ 极(填“N”或“S”); 

(3)滑片P向A端移动时,甲的磁性将____ (填“变大”“变小”或“不变”)说明了____ .

(4)通过电磁铁甲的电流____ 流过电磁铁乙的电流(填“大于”“小于”或“等于”).电磁铁甲、乙磁性强弱不同的原因是____ .

 

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答案(点此获取答案解析)

吸引大头针的个数,N,变大,匝数相同时,电流越大,电磁铁的磁性越强,等于,匝数不同

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       Some thing in chocolate could be used to stop coughs and lead to more effective medicines,say UK researchers.

Theirstudy found that theobromine, found in cocoa, was nearly a third more effectivein stopping coughs than codeine, which was considered the best cough medicineat present.

    The   Imperial College London researchers who published their results online said thediscovery could lead to more effective cough treatment. “While coughing is notnecessarily harmful, it can have a major effect on the quality of life, andthis discovery could be a huge step forward in treating this problem,” said Professor Peter Barnes.

Tenhealthy volunteers were given theobromine, codeine or placebo, a pill thatcontains no medicine, during the experiment. Neither the volunteers nor theresearchers knew who received which pill. The researchers then measured levelsof capsaicin(辣椒素),which is used in research to cause coughing and as a sign of how well themedicines are stopping coughs.

Theteam found that, when the volunteers were given theobromine, the capsaicin needto produce a cough was around a third higher than in the placebo group. Whenthey were given codeine they need only slightly higher levers of capsaicin tocause a cough compared with the placebo.

   There searchers said that theobromine worked by keeping down a verve activity(神经活动), which caused coughing. They alsofound that unlike some standard cough treatments, theobromine caused no sideeffects such as sleepiness.