问题 计算题

探索班为了解决同学们的饮水问题,购置了一台饮水机,其铭牌如下表所示。图12是

饮水机的电路图,S是用感温材料制造的温控开关,R1是电阻,R2是供加热的电阻丝。

额定频率50Hz环境温度10℃~38℃
加热功率550W 环境湿度≤90%
额定电压220V 制热水能力≥90℃ 5L/h
 

(1)、用公式分析, S处于什么状态(闭合或S断开),饮水机处于保温状态。(1分)

(2)、在加热状态下,饮水机正常工作时电路中的电流是多大?(1分)

(3)、在饮水机的热水罐中0.6kg水,正常工作,使水从30℃的加热到80℃,用了5min20秒时间。用这些信息及数据,计算热水罐中的水吸收的热量和该饮水机加热状态时的效率。[C水=4.2×103J /(kg·℃)](2分)

(4)、如果要使饮水机在加热状态时的功率是保温状态时的4倍,则R1与R2的比值应是多少?( 2分)

答案

(1)略

(2)2.5A

(3)1.26×105J

(4)3:1

根据公式可知电源电压不变,功率和电阻成反比,S处于闭合状态是加热,S处于断开状态是保温。在加热状态下,功率是550W,饮水机正常工作时电路中的电流利用公式I=P/U求出;在饮水机的热水罐中0.6kg水,正常工作,使水从30℃的加热到80℃,根据Q=Cmt计算出水吸收的热量。根据水吸收的热量和5min20秒时间内消耗的电能计算该饮水机加热状态时的效率。如果要使饮水机在加热状态时的功率是保温状态时的4倍,根据公式可知加热时电阻是保温时电阻的1/4。所以R1与R2的比值应是3:1。

填空题

Part 4


Questions 26-45


·Read the following passage and decide which answer best fits each space.
·Forquestions26-45, markoneletterA, B, C or D on the Answer Sheet.
Both (26) and zoology are parts of a more general field of science, biology. The two are studies of (27) things, which share certain characteristics, (28) they are plants or animals. Botany deals with plants, whose organisms that can (29) their own food by the use of sunlight. Zoology on (30) hand, deals with animals, those organisms that cannot manufacture their own food and are thus dependent (31) plants for their food.
(32) plants and animals share many abilities, the extent (33) which plants can exercise some of those abilities is (34) . For example, both plants and animals need food, water, and warmth for growth, (35) plants can move to (36) those needs only by the slow extraction of their leaves and roots, while animals can move relatively (37) distances in relatively little time. When an animal is hurt with needle, the animal will (38) the part of the body (39) . This ability to draw back (40) pain or irritation, called irritability, is found only to a very limited extent in plants.
If plants (41) the same (42) as animals, animals would have had a more difficult time finding food. If animals were as limited as plants, they might (43) a means of manufacturing their own food, as plants do now. The world would be a very different place (44) it is if the characteristics of plants and animals were (45)

A.acquire

B.require

C.admit

D.constitute

单项选择题