## The Things I Learn….

27 Jul

Out of boredom and because I’m a poor test-taker, I’ve decided to start doing one Physics GRE question a day. My first question was relatively simple:

Two harmonic transverse waves of the same frequency with displacements at right angles to each other can be represented by the equations

y = (y`0`)sin(wt – kx)

z = (z`0`)sin(wt – kx + Φ)

The equations represent a plane-polarized wave if Φ equals: __

I know the answer. Of course I know the answer. We spent two whole weeks on waves last semester, and we were supposed to (but didn’t) spend time in the fall covering simple harmonic motion, which is an introduction to waves. The answer is zero, because the waves are already at right angles to each other (to those curious, phi is an angle of displacement), and have the same frequency. Yet still I answered pi/2, which is wrong because then the waves would be out of phase, and plane-polarization depends on the waves being in phase*.

And so I learned my first lesson: don’t read the questions too quickly. Oh, well. Gotta start somewhere, I suppose.

*As always, there’s the potential that I may be wrong, or that my explanation is incomplete. If you spot it when this happens, please speak up! Memory is fallible, and I’d rather have someone point out when I’ve got something wrong than think a faulty explanation is correct.