问题 选择题

如下图甲所示的热熔胶枪是一种装修工具,用于材料涂胶。它的内部有2只相同的PTC(是一种新型的半导体陶瓷材料,它的发热效率较高 正温度系数)加热元件,其工作电路如下图乙所示,扣动扳机能使固体胶条向前挤压,联动开关S同时掷向A、B,枪口冒出胶液,松开扳机,联动开关S同时掷向B、C。单只PTC元件的电阻随温度的变化如下图丙所示。关于PTC元件的工作情况,下列说法正确的是(    )

A.扣动扳机,两只PTC元件串联在电路中

B.松开扳机,只有一只PTC元件接入电路

C.松开扳机,当温度为80℃时,电路消耗的电功率为55W

D.扣动扳机,当温度为180℃时,1min电路消耗的电能为4800J

答案

答案:D

题目分析:(1)扣动扳机时,联动开关S同时掷向A、B,电路如下图所示:

两只PTC元件并联在电路中,当温度为180℃时,R1=R2=1210Ω,

∴1min电路消耗的电能:

所以A选项错误,D选项正确.

(2)松开扳机时,联动开关S同时掷向B、C,电路如下图所示:

两只PTC元件串联在电路中,当温度为80℃时,R1=R2=880Ω,

∴电路消耗的电功率:

所以B、C选项错误.

所以选D.

点评:本题考查了学生对欧姆定律、电功率公式的掌握和运用,能读懂电路图中开关对元件的控制作用,是解决本题的关键,考查了学生的读图分析能力.

单项选择题
阅读理解

阅读理解。

     From the earliest times, man has been interested in art. People have often worked together to collect and

save the world's art treasures.

     Fine art treasures from many countries are kept in an art museum called the Louvre in Paris, France. The

works of art have been collected by the people of France over many centuries. The Louvre has not always

been a museum. The first building was a fort (炮台). In 1190, it was the king's castle with high walls and a

round tower. It had a moat to prevent his enemies from walking in.

     Over the years, the number of buildings around the castle grew. By 1350, the castle was no longer needed

as a fort. The Louvre became a palace home for French kings and queens.

     During times of peace, new treasures were brought in. During days of war, many treasures were stolen,

and the buildings were damaged.

     When Francis I became king of France in 1515, he brought in artists from many countries. One of the

artists was Leonardo da Vinci from Italy. Da Vinci's "Mona Lisa" is the best known painting in the museum

today.

     In 1793, the Louvre became a public museum, just as it is now. It is a place where art treasures have been

saved for everyone to enjoy.

1. How long has the Louvre been a museum?

A. For over 800 years.

B. Since 1350.

C. Since 1515.

D. For over 200 years.

2. Most of the works of art in the Louvre have been collected probably_____.

A. by the French people

B. by Francis I

C. by Leonardo Da Vinci

D. by people of the world

3. From the passage we can learn that _____.

A. the Louvre was once a church as well as a palace

B. Mona Lisa is kept in Italy

C. Da VinCi once stayed in France

D. the Louvre is only a place of interest to the French people

4. Why is it good for the works of art to be kept in public museums?

A. In public museums works of art will not be stolen.

B. In public museums works of art will not be damaged.

C. In public museums artists can study the works of art.

D. In public museums everyone can enjoy the works of art.