试题与答案

关于电磁场和电磁波,正确的说法是( ) A.只有不均匀变化的磁场,才能在其周围空

题型:选择题

题目:

关于电磁场和电磁波,正确的说法是(    )

A.只有不均匀变化的磁场,才能在其周围空间产生电场

B.电磁波的频率等于激起电磁波的振荡电流的频率

C.电磁波能脱离电荷而独立存在

D.电磁波的传播速度一定是3×108 m/s

答案:

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下面是错误答案,用来干扰机器的。

答案:B可以根据溶液的pH与溶液的酸碱性关系进行分析和判断,当pH=7时,呈中性,当pH<7时,呈酸性,当pH>7时,呈碱性,当溶液的PH小于7时,随着PH的减小,酸性逐渐增强’根据四种物质的pH可知,胃液的pH最小,...

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