问题 问答题

电动机是利用什么原理工作的?为使直流电动机持续转动,必须在直流电动机上安装什么?电动机工作时能量是如何转化的?

答案

电动机,即通电能动,其是利用通电导线在磁场受力的作用;在直流电动机中,为了能使线圈刚刚转过平衡位置时就自动改变线圈中的电流方向,即必须安装“换向器”,从而实现通电线圈在磁场中的连续转动,其实质是将机械能转化为电能的装置.

故答:通电导线在磁场中受力的作用;换向器;电能转化为机械能.

阅读理解

阅读理解。

     Equipped only with a pair of binoculars (双筒望远镜) and ready to spend long hours waiting in all weathers

for a precious glance of a rare bullfinch (红腹灰雀), Britain's birdwatchers had long been supposed to be lovers of a minority sport. But new figures show bird-watching is fast becoming a popular pastime, with almost three million of us absorbed in our fluttering feathered friends.

     Devoted birdwatchers, those prepared to travel thousands of miles for sighting of a rare Siberian bird, are

fast being joined by a new breed of follower whose interest is satiated by watching a few finches (雀科鸣鸟)

on a Sunday walk or putting up a bird-box in the back garden.

     "Almost three million UK birdwatchers is certainly possible if you include everyone with only a casual

interest," Stephen Moss said in his newly published book.-A bird in the Bush: a Social History of Birdwatching

- which records the pursuit from the rich Victorian Englishman's love of shooting rare birds to the less

offensive observational tendencies of birdwatchers today.

     Television wildlife programmes have helped to fuel the new trend. Last summer, BBC 2's Britain Goes

Wild was a surprise success. It pulled in three million views and led to bird-houses selling out across the UK as

45,000 people promised to put up a box. Birdwatchers networking system first came to the attention of the

nation in 1989, when a birdwatcher caught sight of the first Vermivora chrysoptera-a golden-winged songbird

from North America-to be seen in Britain. He put a message out on the network service Birdline, and the next

day 3,000 birdwatchers proved the full pull of a truly rare bird as they visited the Tesco car park in Kent.,

where it had settled. Today, birdwatchers can log on to www.birdline.co.uk or have news of the latest sighting

texted to their phones.

      "Multimillion-pound spending on binoculars, bird food and boxes point to the increasing numbers of

birdwatchers." Said David Croack, the editor of Bird Watching magazine"The number of people involved is so

big that they have great potential to influence government decisions affecting the environment."

1. The word "satiated" in paragraph 2 can best be replaced by "______".

A. affected

B. shared

C. satisfied

D. narrowed

2. What happened after the message of seeing a Vermivora Chrysoptera was put on the network?

A. Birdwatchers helped the rare bird settle in Kent.

B. Large numbers of birdwatchers went to view the bird.

C. Many birdwatchers logged on to the website for details.

D. Birdwatchers showed their determination to protect the rare bird.

3. Which of the following CANNOT be true according to the passage?

A. Television wildlife programmes started the popular pastime of birdwatching.

B. The network service has contributed to the rapid development of birdwatching.

C. Birdwatching in Britain was long considered a sport with a small group of followers.

D. The current situation of birdwatching may promote the protection of the environment.

4. The passage mainly tells us about _______ in UK.

A. the history of birdwatching.

B. a growing passion for birdwatching

C. the impact of media on birdwatching

D. birdwatching as a popular expensive sport

单项选择题