由电源引到某工地的一只“220V、100W”的灯泡亮度较暗，测得该灯_爱下问搜题

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问题问答题

由电源引到某工地的一只“220V、100W”的灯泡亮度较暗，测得该灯泡的实际功率只有81瓦，而电源的电压确为220伏．输电导线上消耗的功率约有多大？你在计算中用到了什么近似？

答案

解（1）：由“220V、100W”知灯泡的额定电压U=220V，额定功率是P=100W，

则灯泡的电阻R=

U2

P

=

(220V)2

100W

=484Ω，

（2）灯泡功率为81W时，灯泡两端的实际电压U_实=

P实R

=

81W×484Ω

=198V；

流过灯泡的实际电流I_实=

P实

U实

=

81W

198V

≈0.41A；

（3）灯泡的电压降U_线=U-U_实=220V-198V=22V；

输电导线上损失的功率P_损=U_损I_实=22V×0.41A≈9W．

灯丝电阻阻值随温度的变化而改变，在计算中认为灯丝的电阻不变，这是一种近似．

答：输电导线上消耗的功率约为9W；在计算中认为电灯灯丝的电阻不随温度改变，这是一种近似．

阅读理解

阅读短文，判断正(T)误(F)。

The horse and his purchaser (买主)

A man wanted to buy a horse. He went to the market, and saw a nice one. But he wanted to test him first.

So he took the horse home, and put him into the stable (马厩) with the other horses. The new horse looked

around, and at once went to choose a place next to the laziest in the stable.

When the man saw this, he put a halter (辔头) on the horse at once, and gave him back to his owner.

The owner felt quite surprised. He asked the man, "Why are you back so soon? Have you tested him

already?" "I don't want to test him any more," answered the man, "From the companion (同伴) he chose for

himself, I could see what kind of animal he is."

( ) 1. The man wanted to buy a good horse.

( ) 2. The new horse chose is the laziest one as his friend.

( ) 3. The man liked the new horse very much.

( ) 4. He didn't give it back to his owner.

( ) 5. From this story, we know the new horse is also a lazy one.

单项选择题

助消化药不宜与抗菌药物、吸附剂同时服用；如必须联用，应间隔的时间是（）

A.1小时

B.1.5小时

C.2小时

D.1～3小时

E.2～3小时