wˌɛɹ ɪz ðə pɹˌɑːbəbˈɪlᵻɾi kˈɜːɹənt ɪnðə wˈeɪv ˈɪnsɪdənt əpˌɑːn ðə bˈæɹiɚ wɪð nˈoːɹməl jˈuːnɪt vˈɛktɚ ænd ɪz ðə pɹˌɑːbəbˈɪlᵻɾi kˈɜːɹənt ɪnðə wˈeɪv mˈuːvɪŋ ɐwˈeɪ fɹʌmðə bˈæɹiɚɹ ɔnðɪ ˈʌðɚ sˈaɪd.
where  is the probability current in the wave incident upon the barrier with normal unit vector  and  is the probability current in the wave moving away from the barrier on the other side.