电荷量为-5.0×10-12C的点电荷A置于电场中的P点，所受电场力大小为2.0×10-6N，方向向右，则P点的电场强度大小为________N/C，方向________（填“向右”或“向左”）．若A电荷在P点具有-1.5×10-11 J的电势能，则P点的电势为________V．若将P点的电荷换成电荷量为+2.0×10-12C的点电荷B，则P点的电场强度大小为________N/C，B电荷的电势能为________J。
4.0×105 向左 3.0 4.0×105 6.0×10-12
题目分析：根据公式
得P点的场强大小为
，方向与负电荷受的电场力方向相反，故电场方向向左，根据公式
得P点的电势为3.0V，电场强度大小跟试探电荷无关，所以将P点的电荷换成电荷量为
的点电荷B，P点的电场强度大小不变，仍为
．B电荷的电势能为
．
点评：应用时电场强度定义式一般不代入符合计算，物理量的方向单独判断，而电势的定义式各量一般要代入正负号．
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| We 16 four new students in our class. One is Tom. He 17 England. He speaks 18. John's 19 the United States. He speaks English, 20.And Michiko 21 a Japanese. She lives 22 Tokyo. But she is in Beijing 23 her parents. The last one is Peter. He's from 24 . He speaks English and French. We are in 25 same class. We are good friends. | |||
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