Ψ= ∫ S D ⋅ e n dA MathType@MTEF@5@5@+=feaagCart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbbjxAHXgarqqtubsr4rNCHbGeaGqipG0dh9qqWrVepG0dbbL8F4rqqrVepeea0xe9LqFf0xc9q8qqaqFn0lXdHiVcFbIOFHK8Feea0dXdar=Jb9hs0dXdHuk9fr=xfr=xfrpeWZqaaeqabiGaciGacaqadmaadaqaaqaaaOqaaGGacKqzafGae8hQdKLccqGH9aqpdaWdrbqaaGqadiaa+readaWgaaWcbaaabeaakiabgwSixdWcbaGaae4uaaqab0Gaey4kIipakiaabccacaGFLbWaaSbaaSqaaiaab6gaaeqaaOGaaeizaGqaciaa9feaaaa@437B@
where endA is the vector surface element