Microwave generator and a resonant cylindrical cavity

[Elsi b]

Homework Statement

A microwave generator can produce microwaves at any frequency between 10.0 GHz and 20.0 GHz. The microwaves are aimed, through a small hole, into a "microwave cavity" that consists of a 10.0cm -long cylinder with reflective ends.

A. Which frequencies between 10 GHz and 20 GHz will create standing waves in the microwave cavity?

Relevant Equations

L=c/f

I tried to fix this physics problem. But i think I’m using the wrong steps.

 

[Keith_McClary]

Like this with v=c.

 

[Elsi b]

Yes I just realized that I was using the wrong method for standing waves cavities, the question was asking about close - close between cylinder microwave cavities... thanks for the hint