问题 问答题

如图所示,灯L上标有“6V3W”字样,开关S闭合,滑片P移至a端时,电流表的示数为1A,且灯L正常发光.

(1)电源电压和滑动变阻器的最大阻值分别为多大?

(2)当开关断开,滑片P移至b端时,电流表的示数为0.25A,此时灯泡的实际功率为多大?

(3)当开关断开,滑片P移至b端时,在1min内灯泡消耗的电能为多大?

答案

(1)开关S闭合,滑片P移至a端时,滑动变阻器都被连入电路,灯泡和变阻器并联,

因为灯泡正常发光,

则电源电压为:U=U=UL额=6V,

∴通过灯泡的电流为:IL额=

PL额
UL额
=
3W
6V
=0.5A,

则通过变阻器的电流为:I=I-IL额=1A-0.5A=0.5A,

∴滑动变阻器的最大阻值为:R=

U
I
=
6V
0.5A
=12Ω.

(2)当开关断开,滑片P移至b端时,滑动变阻器都被连入电路,灯泡和变阻器串联,

而灯泡的电阻为:RL=

UL额2
P额L
=
(6V)2
3W
=12Ω,

而此时电路中的电流为:I′=0.25A,

∴灯泡的实际功率为:P=I′2RL=(0.25A)2×12Ω=0.75W.

(3)∵t=1min=60s,

∴灯泡消耗的电能为:W=Pt=0.75W×60s=45J.

答:(1)电源电压为6V,滑动变阻器的最大阻值为12Ω.

(2)此时灯泡的实际功率为0.75W.

(3)在1min内灯泡消耗的电能为45J.

阅读理解

阅读理解。

     Rembrandt was an extraordinary Dutch painter. He was most well-known for his brushwork and

the way in which he connected with the human soul. His life, however, was not happy.

    He was born on July 15, 1606 in Leiden, the Netherlands. His father wanted him to have a real,

learned profession but Rembrandt left the University of Leiden after becoming bored. He began studying

art under a local teacher but soon left and studied in Amsterdam where he mastered all his lessons in six

months!

     At the age of 22, he moved back to Leiden and began to get his own students. One of his students

was the famous artist Gerrit Dou. In 1631 he returned to Amsterdam where he became the most popular

portrait painter in Holland. Rembrandt met Saskia and married her in 1634. She was a cousin of a very

successful art dealer and she helped him to meet wealthy people who commissioned (委任制作) many

paintings from him. He used her as a model in many of his paintings.

     Rembrandt's private life, however, was very unfortunate. He had four children with Saskia but only

one, Titus, survived. Saskia died in 1642 at the age of only 30. In 1649, his housekeeper became his

second wife and was also a model for many of his paintings. Even though Rembrandt was very successful

as an artist, art dealer and teacher, he lived in a careless way and had to declare bankruptcy (破产) in

1656. He even had to sell his whole art collection and his house to pay off his debts.

     His unfortunate life, however, didn't affect his art. He painted many great paintings during that time.

His new love, Hendrickje, died in 1663 and his 27-year-old son, Titus, died in 1668. Eleven months

later, on October 4, 1669, Rembrandt died in Amsterdam. He produced more than 600 paintings and

over 2,000 drawings!

1. Which of the following is the reason that made his business fail?

A. As an extraordinary Dutch painter, he knew nothing about business.

B. He spent most of his time on art, leaving no time to care his business.

C. All his children but Titus died, which made him very sad.

D. Like other famous artists, he was thoughtless.

2. From the passage we learn that Rembrandt         .

A. graduated from the University of Leiden.  

B. began his teaching career in 1628.

C. married Saskia when he was 22 years old.

D. was good at drawing animals and flowers.

3. How many members of Rembrandt's family died before him, not including his parents?

A. Four  

B. Five  

C. Six  

D. Seven

4. What's the best title for this passage?

A. A brief biography of Rembrandt  

B. A great Dutch painter  

C. The greatest painter in the world  

D. Rembrandt's unhappy family  

填空题