哪位仁兄能帮我划分一下这句话的句子成分？

主语the function of this coil
谓语is
不定式做表语to create a very strong electromagnetic field
when引导的时间状语从句，当。。。的时候，也可以放在句末。
The function of this coil is to create a very strong electromagnetic field when current passes through it .