试题与答案

如图所示的电路中,电源电压保持不变,当S断开时,电流表的示数为2安,这时电阻R1

题型:计算题

题目:

如图所示的电路中,电源电压保持不变,当S断开时,电流表的示数为2安,这时电阻R1消耗的电功率为12瓦,当S闭合后,电流表的示数为3安,问:

(1)电阻R1、R2的阻值是多少?

(2)当开关S闭合后,电阻R2在5分钟内产生的热量是多少?

答案:

(1)∵I1=2A,P1=12W,∴R1===3Ω,

又∵I=3A, ∴I2=I﹣I1=3A﹣2A=1A,

U2=U1=I1R1=2A×3Ω=6V,

R2===6Ω.

(2)∵I2=1A,R2=6Ω,t=5min=300s,

∴Q2=I22R2t=(IA)2×6Ω×300s=1800J.

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题型:阅读理解

阅读理解。

     Around the world more and more people are taking part in dangerous sports and activities. Of course, there have always been people who have looked for adventure (冒险)-those who have climbed the highest mountains or explored unknown parts of the world. Now, howev-er, there are people who look for a quick pleasure from a dangerous activity, which may only last a few minutes or even seconds.

     I think bungee jumping is a good example of such an activity. Yet jump from a high place(maybe a bridge or a hot-air balloon (气球) 200 meters above the ground with an elastic rope ( 弹力绳 ) to your ankles (踝). You fall at up to 150 kilometers an hour until the rope stops you from hitting the ground. It is said that 2, 000, 000 people around the world have now tried bungee jump-ing. Most people think that other activities, such as jumping from the tall buildings and diving into the sea from the top of high rocks (岩石) are as dangerous as bungee jumping.

     Why do people take part in such activities as these? Some scientists think it is because life in modern societies has become safe and boring. Now life has little excitement. They buy food in shops and there are doctors and hospitals to look after them if they are ill. The answer for some of these people is to look for danger in activities as bungee jumping.

1. How many people have now tried bungee jumping?

A. Two hundred.

B. Two thousand.

C. Two million.

D. Two billion

2. People take part in dangerous sports because_____.

A. people want to get excitement from them

B. they have more free time

C. they hate adventure

D. they are fed up with jumping

3. Which of the following descriptions about bungee jumping is right?

A. It's very boring.

B. It's much easier to do.

C. It takes much shorter time to get pleasure.

D. It's hard to find a place for it.

4. The writer of this passage_____ .

A. is a lover of dangerous activities himself

B. is against dangerous activities

C. mainly tells people about an interesting activity

D. doesn't say whether dangerous activities are good or bad

5. Which of the following picture shows the right way of bungee jumping?

A.  B.  C.  D.

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