题干

某太阳能热水器公司研制出一种新的太阳能、电能两用热水器.天气晴朗时使用太阳能;在阳光不足时,用电热丝辅助加热.实物如图所示,热水器铭牌如表:

**牌热水器

型号﹣18A

集热管数28支

额定频率50Hz

水箱体积200L

集热管管长180cm

额定电压220V

防水等级A

系统水压3.0MPa

额定功率4400W

(1)电热水器正常工作时,电热丝的电阻和电流各是多少?

(2)太阳能热水器贮满水,水温从20℃加热到50℃时吸收了多热量?

(3)若通过完全燃烧天然气加热一满箱水,使其温度从20℃升高到50℃时,不考虑热量的损失,需要多少立方天然气?(天然气的热值为4.0×109J/m3

(4)由于天气不好,太阳能热水器只将水加热到35℃,现要通过电热丝将水加到50℃使用,需电加热器正常工作多少秒?(设电能转化为内能的效率为70%)

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答案(点此获取答案解析)

解:
(1)因为电热水器正常工作,
所以U=U=220V,P=P=4400W;
根据P=IU
可得电热水器正常工作时的电流:
I=
P
U
=

同类题5

根据短文理解,从A、B、C、D四个选项中选择最佳答案填空。

    Philip is a school boy. On his twelfth birthday, he decided to give up eating 1.

    "I don't think it's right to eat animals," he said. "They live on the Earth just like us and they are our friends." Philip's parents were not happy about that. "You are a growing boy," his mother said "You need meat. Don't you want to become healthier and 2?" His mother put some 3, rice and carrots in front of him. "I want you to eat all your food now," she said. "Don't 4 anything." Philip didn't want to make his mother sad. But he ate only the rice and the carrots without touching the beef.

     "You're a silly boy!" said his father 5. "I'm getting very angry with you."

     "I'm sorry, Mum and Dad," answered Philip. "I don't want you to be sad or angry. 6 I really don't want to eat any meat. "

     "Then have some fish, dear," said his mother.

     "Oh no, I can't!" cried Philip. "Fish are living things, too.

     "Well, you can't have 7 to eat at all if you don't eat any meat or fish," said his father.

    The next morning Philip got up hungry. His father walked to the 8 with him and asked to see the teacher. "Is this what you teach the students at school" he asked the teacher. "Philip 9 to eat meat at home. He doesn't listen to what I say. "

    "I don't agree with Philip," replied the teacher. "But I think he is 10 to do what he thinks is right. We teach the students to do that."