[Grammar] When to use present/pas participle as an adjective

[kornvarot]

Dear everyone,

I have always been taught that I should use present participle when it describes an active noun, such as a KILLING machine (a machine which kills others)

But for adjective like DEDICATED, DEVOTED, I do not get it.
When we say a DEDICATED teacher (teacher who dedicates his time to student) -> teacher is an active noun right, but why we use past participle?

Thank you in advance

 

[bhaisahab]

What do you mean by 'active noun'? Where did you learn that 'rule'.