Prolonging undergraduate school to do research I am an electrical engineering (communications) undergraduate student. But my main interest is physics ( and/or CS, esp. it's common fields with physics - but it doesn't affect my question here ), and I want to pursue my graduate studies in physics or computer science. However for application, as an engineering student  I'm at a disadvantage as 


I think my major is not considered rigorous enough by people in those fields 
I don't have much (official) coursework in those fields, although I have studied (and am studying) even more than is expected from physics majors
because of the time I've put in studying ( and more importantly, exploring different areas of) physics and computer science,  my GPA so far is not good in electrical engineering.


So with these circumstances, I think the best or maybe the only way is to continue my studies in physics (and/or related areas) more seriously to do more rather good quality research projects and this way, show my ability and qualification for graduate studies in physics (and/or CS).

But, doing so I'll need more time for these additional studies and projects, and  I think I have to stay one year more at undergraduate school (5 years). Is this considered a negative point in application for graduate school?
No.

Nobody cares how long you took to graduate.  There is no advantage to graduating early, and there is no disadvantage to graduating late.  It is extremely common for students to take more than four years to get an undergraduate degree, especially if they change majors, as you are effectively doing.