对直径为80mm的长圆钢棒通电磁化,要求其表面磁场强度达到3978.85A/m,所需要的磁化电流值为()A
参考答案:1000
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如图所示,一个开口向上的圆筒气缸直立于地面上,距缸底2L处固定一个中心开孔的隔板a,在小孔处装有一个能向下开启的单向阀门b,只有当上部压强大于下部压强时,阀门才开启.C为一质量与摩擦均不计的活塞,开始时隔板以下封闭气体压强为1.1P0(P0为大气压强);隔板以上由活塞c封闭的气体压强为P0,活塞c与隔板距离为L.现对活塞c施加一个竖直向下缓慢增大的力F,设气体温度保持不变,已知F增大到Fo时,可产生向下的压强为0.1P0,活塞与隔板厚度均可不计,求:
(1)当力缓慢增大到2Fo时,活塞c距缸底高度是多少?
(2)当力F增大到多少时,活塞c恰好落到隔板上?