Section 3: Behavior of Waves

Reflection Reflection occurs when a wave strikes an object and bounces off of the object. All types of waves (water, sound, light, etc.) can be reflected. The Law of Reflection – The angle of incidence is equal to the angle of reflection. What the heck does this mean??? Look at figure 14 on page 340 for an example. Basically, the angle of the light that hits an object is equal to the angle of the reflection that bounces off of the object.

Refraction Put a pencil into a glass of water. The pencil appears to be bent as it enters the water in the glass. This “bending” is due to the difference in the speed of light as it moves from one medium to another. In the glass the light first travels through air and then it travels through the water. Refraction is the bending of a wave caused by a change in its speed as it travels from one medium to another.

Refraction of Light in Water Objects underwater usually appear to our eyes to be closer to the surface of the water than they actually are. This illusion is caused by refraction. Your brain interprets the light’s path as a straight line when in reality this is not true.

Diffraction Diffraction occurs when an object causes a wave to change direction and bend around the object. You commonly see diffraction occur in water waves when an object causes the wave to bend into a new direction. Diffraction always occurs when waves pass AROUND an object. See figure 11 A & B on page 510

Diffraction and Wavelength The amount of diffraction of a wave depends on the size of the opening in relation to the wavelength. Sound waves have relatively large wavelengths and tend to diffract easily. Light waves have a very small wavelength and are not as easily diffracted. Think about how you can approach a room and hear shouts from inside long before you can see what is going on inside.

Interference When two waves overlap, interference occurs. Interference is when two or more waves overlap and combine to produce a new wave. The next slide details the two types of interference.

Constructive vs. Destructive Constructive Interference is when waves overlap (are in synch) and the resulting wave is the sum of the waves. When this happens in sound, the resulting sound is louder. Destructive Interference is when waves do not overlap. As a result, the new wave has a weakened amplitude. When this happens in sound, the resulting sound is decreased loudness. See page 511

Standing Waves A standing wave is a special type of wave that is produced when waves equal in amplitude and wavelength meet as they travel in opposite directions. As a result, the waves cancel each other out at an area called the nodes, but the wave continues to vibrate around these areas. Standing waves are very important in the formation of rich musical tones in instruments. See page 512