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Basketball is still a young game. It’s over a hundred years old. In the winter of 1891, a certain college was having some trouble with its boy students. The weather was bad and the students had to stay indoors. As they couldn’t play outdoors, they were unhappy, and some even got into fights from time to time.
Some of the teachers, at the college asked Dr. Naismith to invent a game so that the students might have something to play with. It was not easy to invent such a game because it had to be played indoors , and the court (球场) was not very large.
Dr. Naismith thought for a few days and invented a kind of ball game. It was a fast, wonderful game with much moving and passing of the ball. It was played between two teams. To make a score , the ball had to be thrown into the basket ten feet(英尺) above the floor on the wall . At each end of the court there was such a basket. At first, Dr. Naismith wanted to throw the ball into a box. As he could not find boxes of the right size, he had to use fruit baskets instead. That is how the game got its name.
1. How long is it since basketball was invented?
A. 1000 years B. More than 100 years
C. 1100 years D. Less than 100 years
2. The students felt unhappy because _______.
A. they had much homework to do
B. they often got into fights
C. they couldn’t play outdoors
D. they had little time to study
3. Who asked Dr. Naismith to invent a game?
A. Some students B. Some teachers
C. Some students’ parents D. Some of his friends
4. When a student ______ , he makes a score.
A. receives the ball.
B. throws the ball to another student
C. runs quickly with the ball in his hand
D. throws the ball into the basket
5. Which sentence is right?
A. Dr. Naismith had to use fruit to throw the ball.
B. It was easy to invent the game.
C. The students could go outdoors when the weather was bad.
D. The ball had to be thrown into the basket five feet above the floor.
（1）在图20中，甲为某磁极附近磁感线的方向和分布的示意图，由图可知，该磁极为 ▲ 极，若在l处放置一个小磁针，当小磁针静止时，其指向应是图乙中的 ▲ .
（2）磁敏电阻阻值的大小随磁场的强弱变化而变，图丁是某磁敏电阻R的阻值随磁感应强度B变化的图象，据图线可知，磁敏电阻的阻值随磁感应强度B的增大而▲ ．图线没有过坐标原点，说明 ▲ .
（3）王强设计了一个可以测量该磁敏电阻R的电路如图丙所示，（其中磁敏电阻所处的磁场未画出）．将该磁敏电阻R放置在磁场中的位置某处，测出电阻后，利用R—B特性曲线可以读出相应的磁感应强度.
①在图甲磁场中1处，测得的数据如图20表中所示，则该磁敏电阻的测量值为 ▲ Ω.
②根据该磁敏电阻的R-B特性曲线可知，1处的磁感应强度为 ▲ T.
③在实验过程中，仅将磁敏电阻从1处移至2处，其它条件不变，那么电流表的示数
▲ （填“增大”、“减小”或“不变”）.
④依据上述方法获得的磁感应强度B的测量值与该点实际值存在不小的误差，为尽可能准确反映空间某点磁场的强弱，你认为在选择磁敏电阻时应注意什么问题？ 查看习题详情和答案>>