问题 问答题

如图所示,将一只小门铃放在密闭的玻璃罩内,可清楚地听到铃声

(1)若用抽气机逐渐抽去玻璃罩内的空气,则铃声将会______;

(2)若将玻璃罩内的空气全部抽出,能否听到铃声?______;

(3)停止抽气,并让空气重新进入坡璃罩内,将会______;

(4)这个实验说明______.

答案

(1)因为声音可以在气体、液体和固体中进行传播,所以当用抽气机逐渐抽去玻璃罩内的空气时,因为罩内空气稀薄,所以声音会越来越小;

(2)当抽成真空时,声音就会消失,不能听到声音;

(3)停止抽气,并让空气重新进入坡璃罩内,将会听到声音越来越大.

(4)此实验说明声音的传播需要介质,真空是不能传播声音的.

故答案为:越来越小;不能听到铃声;听到声音越来越大;声音的传播需要介质,真空是不能传播声音的.

选择题
单项选择题

The average person learns most of the 30000~40000 words whose meanings he or she recognizes by hearing them or getting familiar with them in the context or simply absorbing them without conscious effort. The best way to build a good vocabulary, therefore, is to read a great deal and to participate in a lot of good talks. There are relatively few words that we learn permanently by purposefully referring to dictionaries or keeping word lists. However, even those extra few are of value, and no one will make a mistake by working on developing a larger vocabulary. Here are some suggestions of how to do it.

Read plenty of good books. When you come across a new word, or a new meaning of an old word, stop and see if you can understand it from its context. If you can’t, and if you can manage without interrupting the thought of the book too much, look it up in a dictionary or ask somebody and then repeat its meaning to yourself a couple of times. If you are really conscientious, write the word and its meaning in a personal vocabulary list—preferably using it in a sentence, or you can keep a special vocabulary notebook. Go over the list from time to time. Further, try to use a new word in writing or conversation a few times over the next several days.

Listen to good talks and be alert to new words you hear or to new meanings of words you already know. Then treat them just as you treat the new words you read.

Learn and be alert to the parts of words: prefixes, suffixes and roots. Knowing them enables you to make intelligent guesses about the meaning of words.

If you are studying a foreign language, be alert to words in that language which relate to words in English. English has inherited or borrowed much of its vocabulary of 500000~600000 words from Latin, Greek, French, Spanish and German.

When you meet a new word in reading, what should you do()

A. Guess its meaning.

B. Ask somebody.

C. Look it up in a dictionary.

D. All of the above.