questions abt wave(urgent)

1. I suppose you refer to water ripples.There is friction between the travelling ripple and the bottom of the basin. When the depth is shallow, the friction force acting on the ripples at the water surface is stronger than that in deep water. Hence, ripples tend to travel slower in shallow water.Since wavelength = speed of rippple/frequencyNow, the speed of ripple in shallow water is lower, but the frequency remains unchanged, this leads to a shortening of wavelength.
2. Simply speaking, diffraction and interference are inherent properties of waves. Physical laws only give a mathematical description for these properties.

3. Snell's Law of refraction is a result of the Fermat Principle of Least Time. The "sine function" appears because there must be a continuity for the wave crest at the boundary between the two media where refraction occurs.

You may download a simple proof of Snell's Law from the following web-page, which shows how the "sine function" comes into play.

http://courses.phas.ucalgary.ca/phys369/Lecture_Notes/Knudsen/snell's_law.pdf




2010-08-03 13:56:49 補充：
1. Generally in F.3 level, you will not be given the proof of Snell's Law. The Law is taught as an experimental result.

2010-08-03 14:01:23 補充：
2. The wave properties can be explained using Huygen's Principle, which is the basis for the "wave theory of light". Again, in F.3 level, you don't need to bother about this, as it involves very difficult mathematics. You could just treat the effects as results of the properties of wave.

2010-08-03 14:02:20 補充：
Description on Huygen's Principle can be found in the following web-page:
http://www.mathpages.com/home/kmath242/kmath242.htm