How to solve these questions in Physics?

Question

The topics are about Refraction and Diffraction of water waves. How do yo answer these question? I'm really having a hard time understanding these questions. Please help me Wyzanters!

 

1. The wavelength of a wave changes from 3 cm to 2.5 cm as it travels from a deep to a shallow portion. Find the ratio of the speed of the wave in the 2 regions.

2. The angle of refraction is the angle made between the direction of propagation of the refracteed wave (over the glass sheet) and the normal to the boundary. What is the angle of refraction? (Basically we did an experiment on this, and we had a glass sheet slanting down at an angle of incidence of 45°. Two wooden blocks which serves as a barrier was placed at the top and bottom of that glass sheet. After that, due to the straight wave generator, series of plane waves travelled and when it hit the glass sheet, the waves travelled on the side of that glass sheet.)

(Just a bonus question, since I really don't get this principle at all. What is Huygen's Principle in simple terms?)

That's all guys! I really hope you can help me, I really don't know what to do since I'ev searched and tried solving on my own but to no avail. :(

Answer 1

1. If cars traveling on the highway slow down, they get closer together. Likewise, if waves slow down, they get closer together, and the wavelength decreases. If the wavelength goes down from 3 to 2.5cm, then they must have slowed down by the same ratio. 2.5/3 = 5/6, so the velocity in the shallow portion is only 5/6 of the velocity in the deep region.
2. This sounds like they are asking you for the actual value of the angle of refraction in your lab, so without data or a diagram, I can't really give you much information. Google "angle of refraction" and also "Phet refraction" for some help on this.
3. Huygen's principle:
4. If you are at the edge of a pool and push down on the water with your hand, circular wavefronts will spread out. If you and a friend both do this next to each other, you will get a cool interference pattern, the combination of all the crests and troughs from the two of you.
5. If you line the entire edge of the pool with people, and they all push down with their hands at once, the combined waves will make a plane wave that goes straight out. Huygens said that any wave behaves as if it were made from an infinite number of little waves propagating from points on the wavefront.