阿摩線上測驗
17. The first figure shows a closed loop with current i. The loop consists of a half-circle of radius r and a half circle of radius R = 2r. The second figure shows the same half-circles but the small one has been flipped over. The net magnetic field at the common center of the circular sections is B₁ for the first figure and B2 for the second figure. What is the magnitude of the ratio B2 / B1?
(A) 0.75,
(B) 3.0,
(C) 0.10,
(D) 1.5,
(E) 5.0.
(A) 0.75,
(B) 3.0,
(C) 0.10,
(D) 1.5,
(E) 5.0.
答案：登入後查看
統計： A(0), B(1), C(0), D(0), E(0) #3332076
統計： A(0), B(1), C(0), D(0), E(0) #3332076
詳解 (共 2 筆)
助人為本
#7399516
所以這題是強調磁場大小及方向
而這裡要搞清楚直線沒有貢獻
只要看圓弧就好
所以根據必歐沙伐定律
圓弧在圓心產生的磁場大小和半徑成反比
所以小圓的磁場強度是大磁場的2倍
所以第一步分析圖一
大圓弧順時針磁場朝內(貢獻一份)
小圓弧是逆時針磁場朝外(貢獻兩份)
一內一外互相抵銷
所以大圓弧是順時針磁場朝內(貢獻1份)
小圓弧也是順時針也是朝內(貢獻2份)
所以方向相同疊加
所以3/1=3
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