问题 选择题

如图所示,三个灯泡是相同的,而且耐压足够,电源内阻忽略.当单刀双掷开关S接A时,三个灯亮度相同,则S接B时

A.三个灯亮度依然相同

B.甲灯最亮,丙灯不亮

C.甲灯和乙灯亮度相同,丙灯不亮

D.只有丙灯不亮,乙灯最亮

答案

答案:D

题目分析:甲灯串联的是电阻,所以切换交流电直流电对它无影响,那么甲灯亮度与原来相同;

乙灯串联的是线圈,线圈对交流电有感抗,而对直流电影响较小,所以切换成直流电之后乙灯比原来更亮;

丙灯串联的是电容,交流电可以通过电容(电容对交流电的影响为容抗),而直流电不能通过电容,所以丙灯不会亮。

点评:在交流电路中,电容器电感与电阻不同,电容器“通交阻直”,电感线圈“通直隔交”

阅读理解

阅读理解

     首先请阅读下列餐馆的信息:

     A. Pasta House-new Italian restaurant located in the heart of the city.Simple but delicious inexpensive meals.Also has a good range of vegetableonly meals.It's always crowded so be ready to order takeaway

or share a table.Open 11 a. m.to midnight.

     B. A Taste of India-famous for its spicy curries and many southern Indian dishes using chilli.You will

usually be able to find a table during the week but if you're planning to go on the weekend make sure you

book a table in advance.Open noon to midnight.

     C. Paris Match-this is the finest French restaurant in the city.Wonderful food you can enjoy in luxurious surroundings.The perfect place to have a romantic meal or impress a business partner,   but be prepared

for a large bill.Open noon to 2 a. m.Booking essential.

     D. Mountain Diner-not fancy but tasty.Excellent Asian and European dishes.Countryside location

surrounded by forest.It's at least an hour's drive from the city so you might want to stay at the nearby

Mountain Hotel overnight.Open 7 a. m.to 10 p. m.

     E. Owl Caf?-open 24 hours a day the caf? has a large selection of set breakfast,   lunch and dinner

meals for you to choose from,   or you can enjoy one of their many delicious snacks and desserts over a

cup of freshly made coffee.

     F. Greek Bistro-a lively restaurant that serves greatvalue Greek food and has live Greek music played by a local band.Customers are encouraged to take part in the entertainment so be ready for a night of loud fun and laughter.Open 6 p. m.to 2 a. m.

     以下是五个人的选择要求,请匹配每个人应选择的地方。

     1. Bill-was late getting up today so hasn't had time to make breakfast.He wants to pick up something to eat before he goes to work so he has enough energy to last through to lunch time.

     2. Julie-works in the city and wants to get some lunch.She doesn't want anything too special so long as

it is tasty and not too expensive.Julie likes all kinds of food but because she is on a diet she wants to avoid anything containing meat.

     3. Sally-has friends visiting her from outoftown and wants to take them to dinner.She wants to take them somewhere they can enjoy the atmosphere and have fun.She is a university student so doesn't have a lot of money and doesn't like her food too hot.

     4. Albert-is a businessman who will meet an important European client for a business dinner next week.Want to book a table at a quiet restaurant that will impress his guest with both its food and its

surroundings.

     5. Robert-is meeting his friend Ben for lunch today (Tuesday) and wants to take him to a nice

restaurant.Both Robert and Ben enjoy good quality spicy food.Robert doesn't like arranging things in

advance so he hasn't booked a table.

1. ________      2.________      3.________     4. ________      5.________

单项选择题