If the wave speeds up in the new medium it turns away from the perpendicular to the medium surface.
When you look at a stick which emerges from water it looks like it is bent. This is because the light from below the surface of the water bends when it leaves the water. Your eyes project the light back in a straight line and so the object looks like it is a different place.
Properties of Waves : Interference
If two waves meet interesting moochers cone happen. Waves are basically collective motion of particles. So when two waves meet they both try to impose their collective motion on the particles. This cone have quite different results.
If two identical (same wavelength, amplitude and frequency) waves are both trying to form a peak then they are able to achieve the sum of their efforts. The resulting motion will be a peak which has a height which is the sum of the heights of the two waves. If two waves are both trying to form a trough in the same place then a deeper trough is formed, the depth of which is the sum of the depths of the two waves. Now in this case the two waves have been trying to do the same thing and so add together constructively. This is called constructive interference.
If one wave is trying to form a peak and the other is trying to form a trough then they are competing to do different moochers . In this case they cone cancel out. The height of the peak less the depth of the trough will be the resulting effect. If the depth of the trough is the same as the height of the peak nothing will happen. If the height of the peak is bigger thone the depth of