问题 探究题

实验探究:电功率跟电流、电压的关系

器材:“2.5V 0.3A”灯泡 、 “3.8V 0.3A”灯泡各一只;电压表、电流表各一只;电池3节、开关1个、导线若干。

(1)探究电功率跟电流、电压的关系,应该采用什么方法?____________________________。

(2)请同学们设计探究电功率跟电流关系的电路图?并设计实验记录表格。

结论:用电器两端的电压相同时,通过用电器的电流越大,电功率_____________。

(3)请同学们设计探究电功率跟电压关系的电路图?并设计实验记录表格。

结论:通过用电器的电流相同时,用电器上的电压越大,电功率_____________。

根据进一步的实验,可得:电功率等于____________,写成公式是___________。

答案

(1)控制变量法

(2)“略” 越大

(3)“略” 越大;电压与电流的乘积;P=UI

阅读理解

B

Modern Manners

Philip Howard answers your questions on contemporary etiquette (礼仪)

Philip Howard,

When my friend and I (two ladies of a certain age) go out to have a meal, she always leaves an extremely large tip. At times, the tip will equal the amount of one of the main dishes—sometimes it comes to about 30 per cent of the bill. I feel 15—20 per cent is adequate for services offered and depending on the type of restaurant. At a cafe I would like to leave 15 per cent or a bit more depending on the service and etc. A larger tip would be appropriate if we are in a big city or a nicer place. My friend says “Well, I am sure they are not driving a Mercedes (奔驰汽车).” Well, neither am I, and how does she know? Who is correct and how can I make changes? I might add I do truly feel tipping should be based on good service, and also if you frequent a place and know the staff a larger tip is OK. I would never hesitate to tip a waitperson. I always leave to the higher side.  

Yours,

Barbara Bade

Barbara Bade,

Americans are more generous tippers than the British. I suspect that 10 per cent for a tip is about normal in the UK. Tipping is a strange survival in our age of supposed equality and minimum wages. Your friend has a generous nature and deep purse. I do not see why you cannot let her tip whatever she wants, and do your own thing. I agree that a tip should be a reward for good service and general good feeling. If the service is rotten and the meal a disaster, we should withhold a tip and explain why we are doing so. Few of us have the chutzpah (厚颜) to do this. Sensible restaurants have a box for tips, so that they are shared out among the staff, including those in the kitchens whom we do not see. (I trust that the management does not receive the money as extra profit.) I look forward to the day when waiters and other servants are paid a good enough living wage, so that they do not have to depend on the generosity of strangers to survive. To wait at table is just as honorable a way to earn a living in this wicked world. If you are pleased with the meal and cheerful service, you should tip as handsomely as your purse affords. I don’t suppose that your waiter / waitress is driving a Mercedes, even in the States. 

Yours,

Philip Howard

60. We can learn from the first letter that Barbara prefers ___________.

A. changing her own ideas on how to tip waiters

B. leaving a bigger tip to the familiar waitpersons

C. eating at a café rather than in a nice restaurant

D. saving as much money as possible for herself

61. It can be inferred that Barbara’s friend tips waiters heavily ________.

A. to show that she is well off                              B. because they are thought to be poorly paid

C. to show that she is generous                          D. because they have offered her full service

62. Besides quality of service, Philip regards __________ as principles of tipping.

A. taste of food and amount of one’s money

B. taste of food and the number of servants

C. generosity of strangers and the number of servants

D. amount of one’s money and generosity of strangers

单项选择题