如图所示,真空中一长直导线通有电流I(t)=I 0 e -λt (式中I 0 、λ为常量,t为时间),有一带滑动边的矩形导线框与长直导线平行共面,二者相距a,矩形线框的滑动边与长直导线垂直,它的长度为b,并且以匀速(方向平行长直导线)滑动,若忽略线框中的自感电动势,并设开始时滑动边与对边重合,试求任意时刻t在矩形线框内的感应电动势ε i 并讨论ε i 方向。
【简答题】听下面一段对话,回答第1至3题。 1. What is the first step in preparing for a speech? [ ] A. Realizing the speech's importance to you. B. Getting a good grade for the speaking assignment. C. Developing the main i...
【简答题】听对话,回答问题。 1. What is the first word the baby tried to say? A. Truck. B. Luck. C. Duck 2. How old was the baby when he learned to say that word correctly? A. About 18 months. B. About 21 months. C. Abo...