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Here’s an amazing way to get a hard-boiled egg into a bottle, even though the mouth of the boiled is smaller than the egg! What’s more, you don’t even need to touch the egg to get it to go in! For this experiment you will need: ·a hard-boiled egg ·a glass bottle with a mouth just slightly smaller than the egg (a fruit-drink bottle works well) ·a 8-cm by 8-cm(3-inch by 3-inch)piece of newspaper ·a match Remove the shell from the egg. Set the egg on the mouth of the bottle to see that the egg does not fit through the mouth. Light the paper. Remove the egg from the mouth of the bottle and drop the burning paper into the bottle. Before the fire goes out, set the egg back onto the mouth of the bottle. Within a few seconds the egg will squeeze(挤) through the mouth and into the bottle. As it entered the bottle, the egg may have broken into pieces. This happens when the diameter(直径) of the egg is more than about 0.5 cm(about 3/16 inch) larger than the diameter of the bottle’s opening. Why does the egg slide into the bottle, even though no one is pushing it? Because the pressure of the air is pushing it. Before the burning paper is put into the bottle, the pressure of the air inside is the same as outside. The burning paper, however, heats the air inside. This causes the air inside to expand. When the egg is placed on top of the bottle, it seals(封住) the bottle. When the fire goes out, the air inside cools. As it cools, the air contracts(紧缩), and the pressure of the air inside becomes less than the pressure outside. Then, the higher outside pressure pushes the egg into the bottle! 小题1:The best title of this passage can be . A.An interesting story B.The pressure of the air C.Egg in a bottle D.Egg, bottle and match 小题2:What don’t you need in this experiment? A.Eggs. B.Water. C.Bottles. D.Paper. 小题3:Why will the egg break into pieces while entering the bottle? A.Because of the burning paper. B.Because the diameter of the egg is too larger than that of the bottles opening. C.Because it is cool inside the bottle. D.Because the pressure of the air inside is larger. 小题4:What is the most important to get the egg into a bottle? A.A match. B.A fruit-drink bottle. C.The pressure of the air. D.The burning paper.
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【简答题】按照题目要求作图. (1)如图甲所示,重物随升降机一起向上做匀速直线运动,请画出重物所受重力和支持力的示意图. (2)图乙是一个不完整的电路图,其中箭头所指的方向表示电路接通时的电流方向,请在图中两个空缺的位置分别补画电池和电压表的符号,使之成为一个完整的串联电路. (3)如图丙所示,小磁针静止在通电螺线管的正右方,请根据磁感线方向,在图中标出小磁针的N、S极和电源的正、负极.
【简答题】已知放大电路输入信号电压为1mV,输出电压为1V,加入负反馈后,为达到同样输出时需要的输入信号为10mV,该电路的反馈系数F为()
【单选题】关于腰椎间盘突出症体征叙述错误的是
A.
腰椎侧凸具有辅助诊断价值
B.
几乎全部患者有不同程度的腰部活动受限
C.
大多数患者在病变间隙的棘突间有压痛
D.
大多数患者有肌力下降
E.
直腿抬高试验及加强试验多为阴性
【简答题】已知放大电路输入信号电压为1mV,输出电压为1V,加入负反馈后,为达到同样输出时需要加的输入信号为50mV,那么电路的反馈系数为( )。
【单选题】已知放大电路输入信号电压为1mV,输出电压为1V,加入反馈后,为达到同样输出时需要的输入信号为 10mV,该电路的反馈深度为 ,反馈系数为 。
A.
10 , 0.009
B.
100 , 0.009
C.
100 , 0.9
D.
10 , 0.09
【判断题】电路中的电流、电压所标的方向是指电流、电压的实际方向。( )A. 对 B. 错
A.
正确
B.
错误
【单选题】若已知 ,则它们之间的相位关系称为()。
A.
同相
B.
反相
【单选题】若已知 , ,则它们之间的相位 关系称为( )。
A.
u 超前 i
B.
u 滞后 i
C.
u 超前 i
D.
u 滞后 i
【单选题】测量流体流量时,随着流体流量的增大,孔板流量计两端压差值( )。
A.
增大
B.
减小
C.
不变
D.
不确定
【简答题】测量流体流量时,随着流体流量的增大,转子流量计两端压差值_______;孔板流量计两端压差值_______。
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