在直径为d的圆形区域内存在着均匀磁场,磁感应强度为B,磁场方向垂直于圆面指向纸外

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问题:

在直径为d的圆形区域内存在着均匀磁场,磁感应强度为B,磁场方向垂直于圆面指向纸外.一电荷量为q、质量为m的带正电粒子,从磁场区域的一条直径AC上的A点沿纸面射入磁场,其速度方向与AC成a=15°角,如图所示.若此粒子在磁场区域运动过程,速度的方向一共改变了90°.重力可忽略不计,求:

(1)该粒子在磁场区域内运动所用的时间t.

(2)该粒子射入时的速度大小v.

考点:向心力牛顿第二定律带电粒子在匀强磁场中的运动
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DRAPL上的破鳞机是干式的。

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股四头肌()。

A.L2

B.L3

C.L4

D.L5

E.S1

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To compete in today’s fast-paced competitive environment, organizations are increasingly allowing contractors, partners, visitors and guests to access their internal enterprise networks. These users may connect to the network through wired ports in conference rooms or offices, or via wireless access points. In allowing this open access for third parties, LANs become (171) . Third parties can introduce risk in a variety of ways from connecting with an infected laptop to unauthorized access of network resources to (172) activity. For many organizations, however, the operational complexity and costs to ensure safe third party network access have been prohibitive. Fifty-two percent of surveyed CISOs state that they currently use a moat and castle’s security approach, and admit that defenses inside the perimeter are weak. Threats from internal users are also increasingly a cause for security concerns. Employees with malicious intent can launch (173) of service attacks or steal (174) information by snooping the network. As they access the corporate network, mobile and remote users inadvertently can infect the network with (175) and worms acquired from unprotected public networks. Hackers masquerading as internal users can take advantage of weak internal security to gain access to confidential information.

A.reserved

B.confidential

C.complete

D.mysterious

题型:问答题

在正常情况下,电压互感器误差受二次负荷影响,误差随着负荷增大而减少

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下列选项中,脑膜瘤的典型CT表现是()

A.钙化、囊变坏死

B.骨质破坏

C.明显瘤周水肿

D.占位效应明显

E.多为等密度,明显均匀增强

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