Physics of Water Waves :: Lab Report

All waves possess the properties of reflection, refraction, diffraction and interference. These phenomena's were observed with the use of a ripple tank. A ripple tank consists of a large rectangular tray with a transparent bottom. Water is placed in this tan to a depth of approximately one centimeter. A light source is then placed above the tray of water. When the water is disturbed it can be seen on a white surface positioned under the tray. The first phenomenon observed was reflection. It was found that water waves also follow the law of reflection. As straight waves strike a hard straight surface they are reflected at an angle equal to the angle of incidence. After reflection the wave has the same speed, frequency and wavelength as it did prior to the collision. This is similar to the reflection of circular waves off a straight barrier. The reflected waves are also circular, however they have a centre point that is position behind the barrier. This point is known as the "image" of the source. Reflection of a parabolic or concave barrier can be closely compared to that of light waves off a concave mirror. If the incident wave was straight, the reflected waves are curved, and they converge at a fixed focal point. After passing through the focus, the radius of the curves increase. The opposite is so when circular waves strike a concave barrier. The reflected waves are then straight. The next phenomenon observed was the refraction of water waves. The refraction was demonstrated in the ripple tank by dividing the tank into a deep and shallow region. This was achieved by placing a rectangular object into one end of the tank. When straight waves travel from a deep region of water into a shallow region, it is found that the speed of the waves is slower in the shallower region. Since the frequency of the wave stages the same, it is obvious that there must be a corresponding decrease in wavelength. If the waves pass from deep to shallow water at an angle other than