问题
填空题
如图所示，真空中带电荷量分别为＋Q和－Q的点电荷A、B相距r。两点电荷连线的中点O处的电场强度大小为 。
答案
；方向：沿OB线，指向B
题目分析: 两个等量异种点电荷在中点产生的电场强度大小相等，方向相同．大小为
则合电场强度E=
=
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如图所示，真空中带电荷量分别为＋Q和－Q的点电荷A、B相距r。两点电荷连线的中点O处的电场强度大小为 。
；方向：沿OB线，指向B
题目分析: 两个等量异种点电荷在中点产生的电场强度大小相等，方向相同．大小为
则合电场强度E==
| It may be necessary, in order that .future (51) can enjoy clean air, that more of the (52) is borne by long-term central government fund．As air pollution varies enormously from place to place and can, indeed, be very local, it may also be necessary for the central government to (53) money so that local authorities can (54) special local problems. That these can be significant was shown by the report made in 1970 (55) behalf of the London Boroughs Association. This (56) that in central London since 1958 smoke concentrations have decreased by 80 percent, whereas sunshine has increased by 70 percent and winter visibility has (57) threefold, There have been (58) in mortality and hospital admissions (59) with air pollution and in the response to it of bronchitis, as well as clear if less documented increases in plant types and bird (60) n the cities. |
A．fee
B．tuition
C．cost
D．charge