问题 问答题

小明家的太阳能热水器,可以贮水100kg,天气好时,吸收的太阳辐射能可以使水温升得足够高;阴雨天可用电辅助加热,它的电加热棒的额定电压是220V,额定功率是2000W.

(1)若在阳光的照射下,100kg的水温从20℃上升到50℃,吸收太阳的热量是多少?[水的比热c=4.2×103J/(kg•℃)]

(2)若在阴雨天仅用电热加热棒在额定电压下将这些水加热,使之升高相同的温度,需要多长的时间?(假设消耗的电能全部转化为水吸收的内能)

(3)实际上用电加热时间需要2h,请你写出产生这种现象的原因.(写出一个即可)

答案

(1)Q=cm(t-t0

=4.2×103J/(kg•℃)×100kg×(50℃一20℃)

=1.26×107J;

答:吸收太阳的热量是1.26×107J;

(2)Q=W=Pt

t=

W
P
=
1.26×107J
2000W
=6300s;

答:需要时间是6300s;

(3)电加热过程存在热损失,或实际电压低于220V.

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SPECIAL EVENTS THIS WEEKEND

Captain Goodfellow

Do your children enjoy interesting stories, funny games, and exciting dances? Captain Goodfellow will be ready to teach all these things to children of all ages at the City Theatre on Saturday morning at 10:00. Free.

Walking Tour of the Town

Forget your worries on Saturday morning. Take a beautiful walk and learn about local history. Meet at the front entrance of City Hall at 9:30. Wear comfortable shoes!

Films at the Museum

Two European films will be shown Saturday afternoon at the Museum Theater. See Broken Window at 1:30. The Workers will be at 3:45. For further information, call 4987898.

International Picnic

Are you tired of eating the same food every day? Come to Central Park on Saturday and enjoy food from all over the world. Delicious and not expensive. Noon to 5:00 pm.

Take Me out to the Ballgame

It’s October, and tonight is your last chance to see the Redbirds this year. Get your tickets at the gate. It might be cold, so don’t forget sweaters and jackets.

Do You Want to Hear “The Zoo”

“The Zoo”, a popular rock group from Australia, will give their first US concert tomorrow night at 8 at Rose Hall, City College.

1. You can probably eat Chinese, Italian, and Arabian food at_______.

A. the front entrance of City Hall                      

B. the City Theatre

C. Rose Hall                                                   

D. Central Park on Saturday

2. You can see movies at the_______.

A. City College                                                      

B. Museum Theater                    

C. City Theater                                                      

D. Central Park

3. If you are going on the Walking Tour, don’t forget to______.

A. take some food                                           

B. tell interesting stories

C. learn about local history                                      

D. wear your comfortable shoes

4. The Redbirds ballgame ______.

A. is held in the afternoon                                           B. might be held outside

C. is held at the gate                                             D. might need sweaters and jackets

5. “The Zoo” is ______.

A. a park with lots of animals there                      

B. a US concert

C. a music group                                                       

D. going to give the concert at 8 am. tomorrow