问题 选择题

如图所示的电路中,电源电压保持不变。闭合电键S后,电路正常工作。过了一会儿,两个电表中只有一个电表的示数变大。灯L和电阻R中的一个可能出现了故障。①若灯L发光,则故障是       ;②若灯L不发光,则故障是         

答案

电阻R短路  电阻R断路

题目分析:本题是灯与电阻的串联电路,电压表测电阻两端电压,电流表测的是串联电流。串联电路中电流只有一条路径,如果一个用电器断开,所有用电器都不能工作。若灯L发光,说明电路中有电流,灯泡正常,只有可能是电阻R短路,相当于导线,电阻为零,电阻两端电压为零。若灯L不发光,电路可能是断路,也可能是灯L短路,若灯L短路,则电流表和电压表示数都会变大,所以灯L不短路;若灯L断路,则电路中没有电流,电阻R两端也没有电压,不符合题意;若电阻R断路,电路中没有电流,电流表示数减小,但电压表正、负接线柱分别能与电源的正负极相连,所以电压表仍有示数,且等于电源电压,所以电压表示数增大,符合题意。

阅读理解

If you watch British television on Friday March 15, you might be surprised to see celebrities wearing funny red noses and joking around. But don’t worry, they’re not mad, it’s all part of a biennial fund-raising event called Red Nose Day.

Organized by the charity Comic Relief, founded in 1985 by two British comedians, the aim of the event is to raise money to fight poverty and injustice in the UK and Africa.

Celebrities and public figures support the event by making appearances on comic TV shows broadcast by the BBC. This year, for example, UK Prime Minister David Cameron appeared in a music video by One Direction, which the band produced for the event.

But Britons don’t just raise money for charitable causes on one day a year, they do it all year round. One way of doing so is by shopping in charity shops.

These small, inconspicuous shops sell clothes, books and household goods just like any other shop. But there’s one big difference—it’s all secondhand.

There are nearly 10,000 charity shops in the UK, according to the Charity Retail Association. Their business model is simple: Anybody who has things they don’t want anymore can donate them to a charity shop, where they are checked for damage, cleaned and priced. Most items go back on sale at a small part of their original price and the money that is made by selling them is used for a charitable cause.

The idea of buying used clothes may sound off-putting, but for shoppers who have less spending money, such as the elderly or those in low-paying jobs, it has been a welcome option for years.

Now, “thrifting”—shopping at charity shops— is also becoming popular with young people looking for alternative fashion.

“I love shopping at thrift stores. You can find very unique clothes for a very cheap price. It doesn’t bother me that other people may have worn them, I simply wash them before I wear them,” said Anne Marie, a 19-year-old Internet user from the US, in a comment on a Yahoo forum.

So next time you spot a charity shop, why not go inside? Who knows, you might find a lovely dress for just a few pounds. Even better, you can enjoy wearing it in the knowledge that your money helped a good cause.

小题1:What do famous people in Britain do in support of the Red Nose Day event?

A.Appear on comic TV shows.

B.Donate large sums of money.

C.Donate expensive clothes to charity shops.

D.Play in a music video with the Prime Minister.小题2:What do we learn from the passage about Comic Relief?

A.It was founded in 1985 by two British comedians in Africa.

B.It organizes the Red Nose Day fund-raising event.

C.It runs nearly 10,000 charity shops in the UK.

D.It is financially supported by the UK government.小题3:One reason for the popularity of the thrift shops is that __________.

A.they sell a wide variety of goods

B.their business model is simple

C.their goods are carefully checked, cleaned and priced

D.they provide things, sometimes special, at low prices小题4:The passage is written mainly to __________.

A.inspire more people to join in charitable causes in the UK

B.introduce the traditions of the Red Nose Day

C.analyze why charity shops are popular in the UK

D.explain how charity shops work in the UK

单项选择题