问题 填空题

一名同学为了研究某种琴弦的发声频率与琴弦长度L及弦内张力T的关系,设计了如图所示的实验:将琴弦一端固定,另一端通过悬挂不同个数的钩码来改变琴弦的张力T,通过改变支撑木条的间距来改变琴弦发声的有效长度L.在只让钩码质量m或只让琴弦有效长度L变化时,测出琴弦振动频率f,并绘出了如下图所示的两个图象.

(1)该同学研究琴弦发声频率与琴弦长度及弦内张力的关系时使用的方法是______.

(2)由图象可知琴弦调节的越紧,所发出的声音频率______(选填“越高”、“不变”、“越低”).

答案

(1)控制一个量不变,研究其他两个量的关系得方法是控制变量法.

所以该同学研究琴弦发声频率与弦长及张力的关系时使用的方法是控制变量法.

(2)琴弦长度一定时,应该画出f-G图象,根据图象可知,琴弦调节的越紧,琴弦内张力越大,所以所发出的声音频率越高.

故答案为:(1)控制变量法;

(2)越高;

单项选择题

Most plants can make their own food from sunlight, (1) some have discovered that stealing is an easier way to live. Thousands of plant species get by (2) photosynthesizing, and over 400 of these species seem to live by pilfering sugars from an underground (3) of fungi(真菌). But in (4) a handful of these plants has this modus operandi been traced to a relatively obscure fungus. To find out how (5) are (6) , mycologist Martin Bidartondo of the University of California at Berkeley and his team looked in their roots. What they found were (7) of a common type of fungus, so (8) that it is found in nearly 70 percent of all plants. The presence of this common fungus in these plants not only (9) at how they survive, says Bidartondo, but also suggests that many ordinary plants might prosper from a little looting, too.

Plants have (10) relations to get what they need to survive. Normal, (11) plants can make their own carbohydrates through photosynthesis, but they still need minerals. Most plants have (12) a symbiotic relationship with a (13) network of what are called my corrhizal fungi, which lies beneath the forest (14) . The fungi help green plants absorb minerals through their roots, and (15) , the plants normally (16) the fungi with sugars, or carbon with a number of plants sharing the same fungal web, it was perhaps (17) that a few cheaters—dubbed epiparasites—would evolve to beat the system. (18) , these plants reversed the flow of carbon, (19) it into their roots from the fungi (20) releasing it as "payment.\

12()

A.created

B.developed

C.designed

D.formulated

单项选择题