问题 单项选择题 A型题

声波由鼓膜经听骨链到达卵圆窗膜时,振动变化的特征是()

A.压强增大,振幅不变

B.压强增大,振幅减小

C.压强增大,振幅增大

D.压强减小,振幅减小

答案

参考答案:B

解析:

本题考点:声波在中耳传递的特点。声波由鼓膜经听骨链到达卵圆窗时,其振动的压强增大,而振幅稍减小,这是中耳增压作用的结果。压强增加的原因有二:鼓膜的振动面积与卵圆窗膜的面积之比为17.2∶1,如果听骨链传递时总压力不变,则卵圆窗的压强比鼓膜增加了17.2倍;通过听骨链的放大作用,压强也被增加了1.3倍;所以二者相乘压力增加了22.4倍。与中耳传音功能有关的还有鼓膜张肌和镫骨肌,当声强过大时,可反射性地引起这两块肌肉收缩,导致鼓膜紧张,听骨链传递的振动幅度减小。

阅读理解

     Vans, Keds, Dollies-they sound like the names of rock bands, but if you have teenagers, you'll know

they're actually the latest in teenage footwear.

     But experts are now warning that the current shoe fashions will be causing teenagers discomfort in the

short term and storing up years of foot, knee and back pain in the future. Here, the experts identify the

problems caused by teenagers' shoe choice.

KEDS/VANS

     Slipon shoes with elastic (弹性的) sides are particularly  popular  among  teenage  boys-with Keds

and Vans the most soughtafter brands.

     The main problem is that they are just too flat-so flat that the heel, which strikes the ground first, also

becomes damaged and painful.

     BALLET PUMPS

     The worst shoes of all are such light and thin dolly shoes. The problem is partly their flatness, as with

Keds and Vans. However ballet pumps, which have no string or heel, have other specific problems.

     "As the shoe has no fastening device, it relies on the toes to keep the shoe on, causing an awkward

gait (步法) , this leads to short-and longterm problems such as calluses (茧子), heel and knee pain."

     WEDGES AND STILETTOS

     These shoes can also cause problems with gait. They may look good, but the heels on these are so

high they can force the wearer's body weight forward, making them very unstable.

Teens who wear these shoes regularly are also in danger of joining those millions of women with constant

back pain.

     SCHOOL SHOES

     So what do podiatrists (足科医生)have on their wish list, especially for everyday wear?

     Something in a natural, breathable fabric, with a string to hold it on, with a small heel and a deep

toebox that does not press the toes, such as Clark's, Marks & Spencer or Rhino.

     If your teen insists on wearing 'bad' shoes, get them some simple foot orthotics(矫形器) in the shoes.

These support and correct the movement of the foot and, properly fitted by a podiatrist, can often

transform their walk and halt the damage.

1. Of all the shoes mentioned in the passage, which can cause the worst problems?

A. Marks & Spencer.

B. Wedges & Stilettos.

C. Keds and Vans.

D. Ballet Pumps.

2. Which pair of shoes may NOT be found on the podiatrists' wish list?

3. The underlined word" halt" in the last paragraph probably means________.

A. increase      

B. worsen      

C. stop          

D. cure

4. From this passage we can infer________.

A. trendy shoes may ruin teenagers' health

B. fashionable shoes all have orthotics in them

C. experts are strongly against wearing popular shoes

D. podiatrists are expert at producing branded shoes

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