如图所示为一种获得高能粒子的装置.环形区域内存在垂直纸面向外、大小可调节的匀强磁

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问题:

如图所示为一种获得高能粒子的装置.环形区域内存在垂直纸面向外、大小可调节的匀强磁场.质量为m、电量为+q的粒子在环中做半径为R的圆周运动.A、B为两块中心开有小孔的极板.原来电势都为零,每当粒子飞经A板时,A板电势升高为+U,B板电势仍保持为零,粒子在两板间电场中得到加速.每当粒子离开B板时,A板电势又降为零.粒子在电场一次次加速下动能不断增大,而绕行半径不变.

(1)设t=0时,粒子静止在A板小孔处,在电场作用下加速.求粒子第一次穿过B板时速度的大小v1

(2)为使粒子始终保持在半径为R的圆轨道上运动,磁场必须周期性递增.求粒子绕行第n圈时磁感应强度的大小Bn

(3)求粒子绕行n圈所需的总时间tn总(设极板间距离远小于R,粒子在A、B极板间运动的时间可忽略不计).

考点:向心力牛顿第二定律带电粒子在电场中运动的综合应用带电粒子在匀强磁场中的运动
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产生推算航向误差的主要原因是()。

A.罗经差的误差

B.操舵不稳

C.风流压差与实际不符

D.A、B、C都对

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什么是翼型的中弧线?

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在金信工程中,市场主体准入管理业务的主要业务中的企业登记业务包括()

A、企业名称的预先核准,企业设立登记

B、企业变更登记

C、企业终止经营登记

D、企业法定代表个人信息登记

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图甲是“位于平原地区的某城市风向频率图”,图乙是“该城市地价分布概念图”(地价等值线数值a、b、c、d、e依次递减),读图回答下列各题。

⑤最有可能分布的城市功能区是()

A.中心商务区

B.行政办公区

C.旅游休憩区

D.科教文化区

题型:问答题


Insurance is the sharing of (1) . Nearly everyone is exposed (2) risk of some sort. The house owner, for example, knows that his (3) can be damaged by fire; the ship owner knows that his vessel may be lost at sea; the breadwinner knows that he may die by (4) and (5) his family in poverty. On the other hand, not every house is damaged by fire or every vessel lost at sea. If these persons each put a (6) stun of money into a pool, there will be enough to (7) the needs of the few who do suffer (8) . In other words the losses of the few are met from the contributions of the (9) . This is the basis of (10) . Those who pay the contributions are known as (11) and those who administer the pool of the contributions as insurer.
The (12) for an insurance naturally depends on how the risk is to happen as suggested (13) past experience. If the companies fix their premiums too (14) , there will be more competition in their branch of insurance and they may lose (15) . On the other hand, if they make the premiums too low, they will not have (16) and may even have to drop out (17) business. So the ordinary forces of supply and (18) keep premiums at a proper (19) to both insurers and those who (20) insurance.

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