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(e=[e]),e.sort().filter((function(t,e,n){if("number"!=typeof t
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r.clientWidth,bottom:n.clientHeight
r.clientHeight,height:n.clientHeight
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0:-1,r=e.isIntersecting?e.intersectionRatio
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基本原理：在有电场存在的情况下，电荷朝电场线方向移动。电荷移动的方向是根据电场中电荷所带电量来决定的。正电荷朝电场方向移动，负电荷朝电场相反的方向移动。电流密度定义为单位时间内通过通过单位面积的带电电荷数。电荷在导体中成为电子。在没有外部电场的作用下，电子是随机运动的，这种情况下导体中不存在电流，电流密度为0。当在导体外部施加电场时，电子就朝电场作用的方向运动。在电场的作用下，导体中就产生了电子和电流。随着电场强度的增强，电子所受的力也逐渐增大，电子移动的速度也要加快。故单位时间内穿过单位面积的电荷数量也增加。因此，随着电场强度的增大，电流密度也增大了。应用条件：导体必须处于外部电场中。具体关系：J=γ.E,
J为电流密度A/m，γ为导体的电导率S/m，E为电场强度V/m