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1、Last week, our economic work Conference held today, held the Countys rural areas for work and five water treatment, three to split Conference, which this year was a matter of Thirteen-Five important meeting of our Countys economic and social development. The main task of the meeting was, on rural wo
2、rk and conscientiously implement the Central, provincial and municipal five water treatment, three to split series of important conferences, learn from the past, study deployment priority tasks this year. Just now, the XXX Deputy head and Deputy County magistrate, respectively, on the work of the XX
3、 was fully deployed, and put forward specific measures and requirements about is in place. County Environmental Protection Bureau, the XX town, town of XX 3 units for a position statement, resounding, demonstrated determination and confidence. Conference also recognition has advanced representative,
4、 this, I also representative County, and County Government, to by recognition of advanced said warm of congratulated! to rural, and water and three modified a split front General cadres workers extend sincere of greeting! following, I again told five points views: a, and deepening awareness, further
5、 enhanced work of sense and urgency since party of 18 session v plenary proposed has innovation, and coordination, and green, and open, and shared five big development concept Hou, rural and environment governance work can said was upgrade to has more high of strategy level, is Thirteen-Five build w
6、ell-off a top priority task. XX, County besides lingxi, Longgang, jinxiang, the Treasury, the hills, several industrial town outside the city centre, is basically belong to other rural areas, area, the vast rural population. Same time, the current and coming period, is the County into a crucial peri
7、od of the South Gate of XX beautiful, environmental regulation directly affects the effectiveness of the strategic objectives can not be achieved. Therefore, the focus on rural work and five water treatment, three to split, the XX economic and social development has an important role. Last year, thr
8、ough the joint efforts of the County, reform of the agricultural and rural development has made great progress in our County, environmental remediation and achieved initial results. Three agriculture agricultural modernization level continues to increase, new 4-level modern agriculture Park, release
9、d 20 agricultural leading enterprises above the county level, the County area of 200 acres of land more than eco-leisure, investments of more than 5 million Yuan reached more than more than 100 agricultural projects. Rural development has improved continuously, boutique line 1 completed the beautifu
10、l countryside, fine village 17, beautiful rural development conference was held in lingxi peach Lake in the city. Promote comprehensive rural reform, included in the provinces building three in one system of farmers cooperative economic organization first promoting the County. Improvement of farmers
11、11第八章 稳恒磁场第八章 稳恒磁场8-1、电流的磁场【基本内容】一、毕奥萨伐尔定律设有通电导线L，在L上以电流元，到场点P的矢径为，如图6.1，则在场点所产生的为：大小：；方向：由与的右手定则确定。真空中磁导率二、磁场叠加原理：在若干个电流或电流元产生的磁场中，某点的磁感应强度等于各个电流或电流元单独存在时在该点所产生的磁感应强度的矢量和。即或三、常见载流体的磁场分布1、载流直导线的磁场分布半无限长直导线的磁场分布：无限长直导线的磁场分布：2、通电圆环轴线上的磁场圆心处x=0：对长为L的圆弧：3、长直螺线管、密绕螺绕环内的磁场【典型例题】利用磁场叠加原理求磁场毕萨定律是计算电流产生磁场的一般
12、方法，应按矢量积分的方法计算。磁场叠加原理：步骤：1、取电流元并求产生的，2、由磁场叠原理求：（1） 若各的方向相同，则直接积分；（2） 若各的方向不相同，则正交分解后积分【例8-1】 闭合载流导线弯成如图例6-1所示的形状，载有电流I，试求：半圆圆心O处的磁感应强度。【解】 闭合导线是由直导线和圆弧线组成，根据载流直导线和圆弧导线产生的磁场公式，可求得各段直线和圆弧线在O点产生的磁感应强度分别为：方向：垂直纸面向外。 方向：垂直纸面向外。 方向：垂直纸面向里。方向：垂直纸面向里。【例8-2】 在一半径R的无限长半圆柱形金属薄片中 ，自上而下地有电流I通过，如图例6-2所示，试求圆柱轴线上任一
13、点P的磁感应强度。【解】 建立例6-2图解坐标系，取宽为的无限长直导线，其通有电流 该电流元在处产生磁感应强度大小：方向：各方向不同。【例8-】 一内半径为a，外半径为b的均匀带电圆环，绕过环心O且与环平面垂直的轴线以角速度逆时针方向旋转，如图例6-。环上所带电量为，求环心O处的磁感应强度。【解】 该圆环的面电荷密度在圆环上取半径为，长为dr的小圆环，如图例6-3图解：其带电量：当带电圆环旋转时，产生圆形电流：该圆形电流在O点处产生的磁感应强度大小：方向：垂直纸面向外。环心O处的磁感应强度方向：垂直纸面向外。8-2、磁场定理【基本内容】一、磁场的高斯定律1、磁感应线磁感应线上每一点的切线方向表
14、示该处磁感应强度的方向；磁感应线的疏密程度表示磁感应强度的大小；磁感应线是无头无尾的闭合曲线。2、磁通量：垂直通过某一面积元dS的磁感应线的根数。通过有限面积S的磁通量则为：3、磁场的高斯定理通过任意闭合曲面的磁通量为零：意义：稳恒磁场是无源场，自然界中没有磁单极存在。二、安培环路定理1、定理的内容：在稳恒磁场中，磁感应强度沿任意闭合路径的线积分等于通过该闭合环路所包围的的所有电流强度I的代数和的0倍。：磁感应强度沿任意闭合回路的积分（环流）。：闭合回路所包围的电流的代数和。I的正负：由所取回路的方向按右手定则确定。2、定理的意义稳恒磁场是一非保守场，是有旋场。【典型例题】用安培环路定理可求解
15、某些磁场的，这些磁场分布有对称性，即激发磁场的电流分布，要有一定的对称性。例如（1）无限长均匀载流圆柱体，无限长均匀载流圆柱面和无限长载流直线产生的磁场在垂直于圆柱轴线的平面上，以轴线上的任一点为圆心，半径为r的圆周上各点的的大小相等，方向沿该点的切线。若安培环路取这样的圆周，且通过需求的点，则可用安培环路定理方便地求出该点的。（2）载流长直螺线管，除去边缘效应管内是匀强磁场，方向沿螺线管的轴线，由于磁场分布的对称性，可方便地用安培环路定理求出这种情况中的。（3）螺绕环，螺绕环内的磁力线是以环心为圆心的同心圆，这种情况也可用安培环路定理求出。步骤：（1）选取积分回路，（2）求沿的环流，（3）求所包围电流强度的代数和，（4）由求。【例8-4】如例6-4图所示，在半径为长直圆柱形导体内，开一个半径为圆柱形空洞，空洞的轴线与导体的轴线平行，相距为，在导体中沿轴线方向通有均匀分布的电流，其电流密度为。（1） 求、处的磁感强度；（2） 证明空腔内磁场均匀。【解】 将此导体等效地看作一个半径为，电流均匀分布的大圆柱体，与另一个半径为、电流密度大小相等、方向相反的小圆柱体组合而成，而磁感应强度应为两圆柱体的磁感应强度叠加而成。（1）轴上一点的磁感应强度为和分
