在如图所示的空间中,存在场强为E的匀强电场,同时存在沿x轴负方向_爱下问搜题

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问题选择题

在如图所示的空间中,存在场强为E的匀强电场,同时存在沿x轴负方向､磁感应强度为B的匀强磁场,一质子(电荷量为e)在该空间恰沿y轴正方向以速度v匀速运动.据此可以判断出( )

A．质子所受电场力大小等于eE,运动中电势能减小;沿z轴正方向电势升高

B．质子所受电场力大小等于eE,运动中电势能增大;沿z轴正方向电势降低

C．质子所受电场力大小等于evB,运动中电势能不变;沿z轴正方向电势升高

D．质子所受电场力大小等于evB,运动中电势能不变;沿z轴正方向电势降低

答案

答案：C

根据粒子匀速运动特点可知,电场力等于洛伦兹力.粒子沿着等势线运动,故电势能不变,电场方向沿z轴向下,故ABD错,C正确.

选择题

2010年世界上很多地方火山喷发，由此产生的火山灰（主要含有二氧化硫、氢氟酸和许多矿物质）给世界航空业带来了巨大的经济损失。下列有关说法中正确的是 [ ]

A．火山喷发产生的火山灰中不可能含有SO₃气体

B．等物质的量的SO₂与Cl₂同时通入水中，所得溶液的漂白性增强，pH减小

C．氢氟酸是一种强酸，可以用细口玻璃瓶盛装氢氟酸

D．一定条件下，足量铁粉与硫的最高价氧化物对应水化物的浓溶液反应，可得到两种气体

完形填空

God’s Coffee
A group of class friends, highly achieved in their careers, got together to visit their old university professor．Conversation soon    31  into complaints about stress(压力) in work and life．
Offering his guests coffee, the professor went to the   32 and returned with a large pot of coffee and a couple of   33  —porcelain, plastic, glass, crystal, some plain looking,    34
expensive, some delicate—telling them to    35   themselves to the coffee．
When all the students had a cup of coffee in 36 ,the professor said：“If you noticed，all the nice looking expensive cups were taken up, 37 behind the plain and cheap ones. While it is
38 for you to choose only the best for yourselves, that is the    39 of your problems and stress．Be sure that the cup itself    40 no quality to the coffee．In most cases it is just more expensive and in some cases even hides what we drink．   41 all of you really wanted was coffee, not the cup, but you consciously (自觉地) went    42 the best cups．And then you began    43  each other’s cups．Now consider this：Life is the   44 ; the jobs, money and position in society are the cups．They are just tools to hold and contain life, and the type of cup we have does not explain , nor   45 the quality of life we   46 . Sometimes, by concentrating only on the cup, we 47 to enjoy the coffee God has 48  us．God brews the coffee, not the cups…Enjoy your coffee!”
The happiest people don’t have the best of everything．They just   49  the best of everything．
Live simply．Love generously．Care deeply．Speak kindly．Leave the   50  to God．

A．living-room

B．waiting-room

B．disagreement