题干

判断,解方程(x-3)÷2=7.5.

解:(x-3)÷2=7.5

(x-3+3)÷2=7.5+3

x÷2=10.5

x÷2×2=10.5×2

x=21

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同类题4

我国建造世界上第一个全超导大型非园托卡马克HT﹣7U,成为国际最先进的磁约束聚变装置.托卡马克装置的主体包括两大部分,就是磁场系统和真空系统.磁场系统包括纵场线圈和加热场的变压器.纵场线圈用来产生强大的纵向磁场,变压器用来感应产生等离子体电流.真空室一般由薄壁不锈钢制成,既要考虑到足够的机械强度,又要有足够的电阻值,还必须留有绝缘缝隙,保证磁场的渗透.抽气系统一般采用大抽速的涡轮分子泵,将真空室抽成10﹣6Pa以上的超高真空,满足等离子体对纯净环境的要求.聚变的第一步是要使燃料处于等离子体态,也即进入物质第四态.等离子体是一种充分电离的、整体呈电中性的气体.在等离子体中,由于高温,电子已获得足够的能量摆脱原子核的束缚,原子核完全裸露,为核子的碰撞准备了条件.当等离子体的温度达到几千万度甚至几亿度时,原子核就可以克服斥力聚合在一起,如果同时还有足够的密度和足够长的热能约束时间,这种聚变反应就可以稳定地持续进行.等离子体的温度、密度和热能约束时间三者乘积称为“聚变三重积”,当它达到1022时,聚变反应输出的功率等于为驱动聚变反应而输入的功率,必须超过这一基本值,聚变反应才能自持进行.

问题1:什么是轻核聚变反应?需要什么条件?为什么要在如此苛刻的条件下进行?

问题2:用普通容器能否承装反应原料?用什么技术性措施能解决该问题?

问题3:如何产生如此强大的磁场?什么叫低温超导现象?该现象是否遵循欧姆定律?超导现象在什么条件下才能实现?

问题4:为什么在托卡马克中设置真空室?核聚变过程中能量是如何转化的?

问题5:核聚变反应需要什么条件才能自持进行?如果等离子体密度大约为1.02×10﹣6kg/m3,温度为1.16×108℃热能约束时间需达到多少时核聚变才能自持进行?

同类题5

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    It was a weeknight. We were a half dozen guys in our late teens, hanging around “the flat” — as usual. The flat was poorly furnished, which, after some time, grew tiresome. We wanted action.

    We got in a car, big enough for all of us to crowd into — and off we went, in search of adventure. We soon found ourselves at Blue Gum Corner, a place named after the huge old blue gum tree that stood by there, a well-known local landmark. It stands at a minor crossroad leading to our town. The trunk is tall and smooth with no handholds for climbing. About six metres from the ground the first branch sticks out over the road. We parked beneath the huge old tree and discussed what we might do. All of a sudden we hit upon an idea — a hanging! I was chosen as “hangee”.

    The plan was quite simple. As I stood upon the roof of the car, the rope (绳子) was threaded down my jacket through my collar and down one leg of my jeans. I put my foot through the loop at the bottom. There I hung, still. The boys rolled about laughing until, a car, I hear a car! Before they ran to hide in the nearby field, they gave me a good push so that “the body” would swing as the car drove by.

    To our disappointment, the car simply turned off for town without even slowing. The boys came out of their hiding places and we discussed the situation. Surely they had seen me, hadn't they? Then we heard another car. The act was repeated, but still without any obvious reaction. We played the game about five or six times, but as no one seemed to notice, we abandoned the trick.

    What we did not know was that every car that had passed had unquestionably seen “the body” and each one, too scared to stop, had driven directly to the local Police Station. Now at that time of the night, the local policeman was sound asleep in his bed, so the first person sent to the scene was the traffic officer that happened to be on duty that particular night. He had been informed that some person had been killed, by hanging, at Blue Gum Corner. When he arrived, the body was gone! And he was hearing “unnatural sounds” from the surrounding area. As far as he knew, some fierce animal was hiding in the field before him, possibly dragging a body behind him — and we thought we were scared!

    He went to his radio and made a call that really began to worry us. I lay so close that I could hear every word. He called for the “armed police” and a “dog team, better make it two” and he had a “serious situation” at Blue Gum Corner. Then the police officer arrived. After a briefing from the traffic officer he decided not to go into the field until armed police and dog teams arrived. Now two spotlights were on the field and none of us could move.

    As luck would have it, police cars cannot leave their spotlights on all night without charging their batteries. So, after a time, the two officers began lightening the field by turns, allowing us the opportunity to move on our fours for freedom. One by one, we all managed to steal away and make our way home. Behind us we left what must have looked like a small city of lights, police cars, roadblocks, barking dogs, armed officers and an old rope hanging from a tree.

    When I think back to that night, to that tree, to what the drivers of the cars think happened, to what police believe happened, and to what I know happened, I am reminded of a simple truth — our eyes see darkness and light, color and movement, our ears hear only vibrations (振动) in the air. It is how we explain these vivid pictures that shapes our “reality”.