Just because the title of this section is “Wave Optics”doesn't mean that it only applies to light! The phenomena we arestudying in this section apply just as well to sound and otherwaves, although for technical reasons they are easiest to observewith light.

In an earthquake waves of several types move through the Earth and along its surface. One type is transverse waves that move along thesurface of the ground (these are the most destructive). You canthink of them as just like the waves you are used to on water, butthey move along the surface of the ground! The speed of these wavesis highly dependent on the nature of the soil or rock at the surface where they are traveling.

Suppose, as shown to the right, a series of surface waves, withwavelength 30.0 m, is traveling north along ground that is a fairlysoft soil. They encounter a series of granite ridges. Because of the abrupt change in the physical properties of the ground the waves will propagate very poorly into the ridges and so the ridgeswill act as a barrier. However, there are two gaps in the ridgeseparated by a distance of 400 m. 10 km beyond the ridges is theedge of a housing subdivision. The point A is roughly in the middleof the edge of the subdivision and is also straight north of thepoint between the two gaps in the ridge.

1.

a) Will a house located at A experience exceptionally large surface waves, or very small ones?
b) What points (relative to A) along the edge of the subdivisionwill experience the largest surface waves? What points willexperience almost no surface waves? Hint: while this is a“double slit” should you use the expressions obtainedin your book for double slits? Under what conditions are those expressions valid?
c) Another house, B, is 3.6 km from one gap and 4.2 km from the other gap as shown. Will it experience large surface waves or smallwaves? Hint: you can determine this very easily using methods fromUnit 2.