If I make an electric circuit for a specific purpose would it be patentable?
The circuit is not complicated, it is simple for a very simple task.
There is nothing particular about electrical circuits that make them unpatentable. Your circuit, if useful, novel, and non-obvious, is likely patentable. If it is a simple thing for a simple task, then it may have already been disclosed by another in which case it would not be novel and therefor not patentable. If the circuit is an obvious variation of something that has been done before, then it may also be rejected.