问题 填空题

电功率的大小

(1)通过用电器的电流相等,用电器上的电压越大,电功率______;用电器两端的电压相同时,通过用电器的电流越大,电功率______.

(2)电功率等于______与______的乘积,公式是______.电流在某段电路上所做的功,跟这段电路两端的______、电路中的______和通电时间成______比,即W=______.

(3)在纯电阻电路中电功率公式的变形:

P=UI=IR•I=______:

P=UI=U•

U
R
=______.

答案

(1)由电功率公式P=UI可知,通过用电器的电流相等,用电器上的电压越大,电功率越大;用电器两端的电压相同时,通过用电器的电流越大,电功率越大.

(2)电功率等于电压与电流的乘积,公式是P=UI.电流在某段电路上所做的功,跟这段电路两端的电压、电路中的电流和通电时间成正比,即W=UIt.

(3)在纯电阻电路中电功率公式的变形:P=UI=IR•I=I2R;P=UI=U•

U
R
=
U2
R

故答案为:(1)越大;越大;(2)电压;电流;P=UI;电压;电流;正比;UIt;(3)I2R;

U2
R

阅读理解

Can dolphins talk? Maybe they can’t talk with words, but they talk with sounds. They show their feelings with sounds.

Dolphins travel in a group. We call a group of fish a “school”. They don’t study, but they travel together.

Dolphins are mammals(哺乳动物), not fish, but they swim together in a school. Dolphins talk to the other dolphins in the school. They give information. They tell when they are happy or sad or afraid. They say“welcome”when a dolphin comes back to the school. They talk when they play.

They make a few sounds above water. They make many more sounds under water. People can’t hear these sounds because they are very, very high. Scientists make tapes of the sounds and study them.

Sometimes people catch a dolphin for a large aquarium.(An aquarium is a zoo for fish.) People can watch the dolphins in a show. Dolphins don’t like to be away from their school in an aquarium. They are sad and lonely.

There are many stories about dolphins. They help people. Sometimes they save somebody’s life. Dolphin meat is good, but people don’t like to kill them. They say that dolphins bring good luck. Many people believe this.

小题1:A school of dolphins means_____.

A.a zoo for dolphins

B.a show by dolphins

C.a group of dolphins

D.a library of dolphins小题2: A dolphin feels _____in an aquarium.

A.afraid

B.happy with people watching them

C.lucky

D.sad and lonely小题3:Which sentence is true?

A.Dolphins talk with words.

B.Dolphins always bring good luck.

C.Dolphins make more sounds above water.

D.Dolphins can’t breathe(呼吸) under the water.小题4:People can’t hear the dolphins’ sounds because they are         .

A.low

B.high

C.soft

D.quiet小题5:From the passage we know_____.

A.Dolphins travel together.

B.Dolphins talk with words when they play.

C.Dolphins like to live in aquariums.

D.All people want to catch dolphins and eat them.

填空题