题干

在光滑水平面上,一质量为m,边长为l的正方形导线框abcd,在水平向右的恒力F的作用下穿过某匀强磁场,该磁场的方向竖直向下.宽度为L(L>l),俯视图如图所示.已知dc边进入磁场时的速度为v0,ab边离开磁场时的速度仍为v0.下列说法正确的是(   )

A:线框进入和离开磁场时产生的感应电流方向相同

B:线框进入和离开磁场时受到的安培力方向相反

C:线框窗过磁场的过程中一直做匀速直线运动

D:线框穿过磁场过程中恒力F做的功等于线框产生的焦耳热

上一题 下一题 0.0难度 选择题 更新时间:2019-07-06 02:34:19

答案(点此获取答案解析)

D

同类题1

任务型阅读

    It's well-known by all the people to greet friends with a smile and a wave.____ However, what happens if your face and body send mixed messages? Would someone tend to believe the look on your face or the way you behave?

    Recently, scientists have dealt with these questions. They found that when a person is staring at your face, he might not believe what he sees if your body doesn't match the feeling that your face shows.____ Previous study had showed that the tone of a person's voice can be more important than the words spoken. For example, most people are more likely not to believe a person who says in a flat voice, “I'm so excited.”

    When talking about emotions conveyed by facial expressions and body language, most scientists suspected that the face was more important. To test if this was true, psychologists from the Netherlands and Boston showed people a number of pictures of isolated faces and isolated bodies that showed anger or fear.____

    An angry face had low eyebrows and tight lips. A frightened face had high eyebrow and a slightly open mouth.____A scared body had arms forward and shoulders square, as if ready to fight back.

These results told the researchers that mixed messages can confuse people. Even when people pay attention to the face, body language surely influences the emotion they read.

    ____And if you want to be understood it helps to avoid sending mixed messages.

A. Studying such mixed messages is nothing new for scientists.

B. So, your body language is important for telling people your feelings.

C. Scientists feel new to study the mixed message that puzzles people.

D. An angry body had arms back and shoulders at an angle, as if ready to fight.

E. Body language can sometimes be misunderstood in different culture backgrounds.

F. They also showed pictures where angry or scared faces were paired with angry or scared bodies.

G. When doing this, your face and body work together to show your friends that you are happy to see them.