Wave Medium Flashcards
what is Huygens Principle?
every point on a wavefront is the source of a spherical wavelet
what is Fermat’s Principle?
That a wave path between two points is that for which the travel time is minumum
how to you get Snell’s Law?
differentiating the distance geometrically between two media, then setting it equal to zero (due to Fermat’s Principle)
what is snell’s law?
sin i1/v1 = sin i2/v2
does velocity increase or decrease with depth?
increases
what is the critical angle in terms of waves, and why is it significant?
critical angle is ic = arcsin(v1/v2) while v2 > v1 , its the angle where the wave travels along the medium interface instead of reflecting or refracting, creating what we call head waves
what is the crossover distance represent (in terms of wave travel)
the distance from the source that waves that went down to the deeper medium arrive before the direct waves (since velocity is faster down there)
describe the concept of polarization of P and S waves and why it’s important
Breaking down what we get from applying helmholtz theorem to navier’s equation, we get u = up + us. we can decompose these into vector components. If we only look at a single plane, the components in the i and k directions have components of p waves (u1) and S saves (u3) while the j direction has components of s waves (u2). greatly simplfies the math for us!
NOTE P and SV waves are related, SH waves are not
sketch a source, and the directions of propagation of p, sh and sv waves
p waves go in the direction of the wave, sv waves are on the page perpendicular to the p waves, and sh waves are in and out of the page
what are P and S wave shadow zones?
due to the way waves reflect/refract thorough different layers of the earth. velocity drops suddenly at the outer core for P waves, and this results in a shadow. S waves dont travel through the liquid outter core so they have a shadow too, larger than the p wave shadow zone.
