磁通量Φ(t)=1/2BπR^2cos(ωt)感应电动势φcd(t)=dΦ(t)/dt=-1/2BπR^2ωsin(ωt)ω=3600/60 r/s=60r/s总电阻α=ρL/S∝ L所以αcd=απR/(πR+2l)电流i(t)=φcd(t)/αcdφcd=1/T∫φcd(t)dt,积分区间是0~T，T=2pi/ωi=1/T∫φcd(t)/αcddt
