题干

我们的生活越来越离不开移动电话了.下列关于移动电话的相关物理知识的描述正确的是(  )

A:移动电话的扬声器处用到了电磁感应现象

B:移动电话是利用电磁波来传递信息的

C:携带信息的电磁波在真空中的传播速度为3×108km/s

D:移动电话机里的所有电路元件都是串联的

上一题 下一题 0.0难度 选择题 更新时间:2019-04-11 11:23:30

答案(点此获取答案解析)

B

同类题4

Crazy is our new normal. With two teenage boys and three little boys, our family is restless- to the baseball field, track field (田径场) and piano lessons. Even though we've limited(限制) each boy's activities and try our best to spare some time for the family, it seems that we're always in a hurry.
"Accept it. Roll with it," my husband, Lonny, says, "It's going to be like this for a while."
He is right. It's likely that life will continue to go forward before it slows down. But I remembered the peaceful, quiet days that our family used to enjoy. I missed long walks through the park when we held the boys' little hands. I wished for lazy Saturday afternoons under the tree in our backyard. I wanted to go back a few years, when busyness was the exception and not the rule(惯例).
One night, after a particularly ful day and evening games, our family gathered on the porch (门廊) for ice cream. Two parents, two teens, and three small boys sat on one old swing and a couple of rocking chairs. We were together, in one place, for a short period of time.
The moon was full. The Mississippi River, flowing past our home, was smooth as glass. I put my own arms around the son who sat on my lap and breathed in deeply his little-boy smell -dirt and sweat. My heart was peaceful and satisfied.
I realized that though crazy is our new normal, happiness is as usual. They may look different from before, but they are still there - even if they're in the form of a single moment on the porch. Maybe I just need the eyes to see.