长直导线周围距导线R处的磁感应强度为B=μ0I/(2πR)。电动势为ε=B1L1v-B2L1v=(B1-B2)L1v=μ0I/(2π)(1/R1-1/R2)L1v=μ0IL1v/(2π)(1/a-1/(a+L2))=μ0IL1L2v/(2π)/(a(a+L2))
书上应该都有
