为什么 “也” 发音为 "ye" 但是 “他”发音为"ta"？？？
Please refer to Old Chinese reconstructions when analysing phonetic components of characters.

他 - Baxter-Sagart OC: /*l̥ˤaj/ > MC: /tʰɑ/ > Mandarin Pinyin: tā

也 - Baxter-Sagart OC: /*lAjʔ/ > MC: /jiaX/ > Mandarin Pinyin: yě


  有部首旁的汉字的发音通常按照没有部首旁的字。


You should probably learn that 部首 is a dictionary indexing tool, and has nothing to do with the functions of character components.