Ek =
r dB | | 2 dt
得
l dB | Eka = | 4 dt
Ekc =
5l dB | | 4 dt
连接oc 连接 、od,分别构成三角形回路 ，分别构成三角形回路obc、ocd,回 、 , 路方向逆时针， 路方向逆时针，由法拉第定律得回路电动势r r dB dφ d ε = = ∫∫ B dS = S dt dt s dt
Q ε ob = ε oa = ε oc = ε od = 0
得 ε bc = ε obc
l 2 dB = | | 4 dt
ε abcd = ε bc + ε cd + ε da
l 2 dB ε cd = ε ocd = | | 2 dt dB 2 | + ε ab = l | dt
