Writing Conditions in Left join sql

I want to know why these queries give different results

    Select *  FROM Table1 T1 
    Left Join MyTable MT 
    ON MT.studentId = T1.StudentId 
    AND T1.class = 7



    Select *  FROM Table1 T1 
    Left Join MyTable MT 
    ON MT.studentId = T1.StudentId 
    WHERE T1.class = 7