TEACHERS: Are you truly learned in your chosen subject?

I'm currently working on getting certified to teach high school science. I was working toward a PhD in mathematical physics, but I wasn't interested in the research at my university and thought it would be interesting and rewarding to try teaching for a bit. I have a masters degree in physics and minored in both mathematics and biology. I also took a lot of chemistry in college. So yes, I'd like to think that I'm truly learned in my subject area. :D In defense of your teachers, sometimes it is difficult to just come up with an answer right there on the spot. I agree though that there are some underqualified teachers who end up teaching a subject that they aren't well versed in because there is a shortage of teachers in their district. I've had several inept instructors over the years...not just in high school.