Wave Behavior
Reflection
it occurs when a wave strikes an object or surface and bounces off and return to the original medium.
An echo is reflected sound. Sound reflects from all surfaces. Your echo bounces off the walls, floor, ceiling,
furniture, and people. You see your face in a mirror or a still pond, as shown in the figure, because of reflection.
Light waves produced by a source of light such as the Sun or a lightbulb bounce off your face, strike the mirror,
and reflect back to your eyes.
When a surface is smooth and even the reflected image is clear and sharp. However, the figure shows that when
light reflects from an uneven or rough surface, you can’t see a sharp image because the reflected light scatters in
many different directions.
The wave "reflects" off the barrier at an angle that is incident to the angle of the wave hitting the barrier.
The incident wave: is a wave that hits the barrier
The reflected wave: is the wave that is reflected from the barrier.
The normal: is the line perpendicular to the barrier where the
incident wave strikes.
Angle of incidence: the angle between the incident wave and the
normal.
Angle of reflection: the angle between the reflected wave and the
normal.
Reflection law:
angle of incidence = angle of reflection.
Refraction
Is the bending of a wave as it moves from one medium into another.
The speed of a wave can be different in different materials. For example, light waves travel faster in air than in
water. Refraction occurs when the speed of a wave changes as it passes from one substance to another, as
shown in the following figure. A line that is perpendicular to the water’s surface is called the normal. When a
light ray passes from air into water, it slows down and bends toward the normal.
When the ray passes from water into air, it speeds up and bends away from the normal. The larger the change in
speed of the light wave is, the larger the change in direction is.
You notice refraction when you look down into a fishbowl. Refraction makes the fish appear to be closer to the
surface and farther away from you than it really is.
Light rays reflected from the fish are bent away from the
normal as they pass from water to air. Your brain interprets
the light that enters your eyes by assuming that light rays
always travel in
straight lines. As a result, the light rays seem to be coming
from a fish that is closer to the surface.
Diffraction
Diffraction occurs when a wave stays in the same medium, but bends around an obstacle. This can occur when
the wave encounters a small object in its path or when the wave is forced through a small opening. An example
of diffraction is when a water wave hits a boat and bends around the boat. The waves after the boat are changed
or diffracted. An example of a diffracted wave passing through a small opening.
Absorption
Absorption is when a wave comes into contact with a medium and causes the medium's molecules to vibrate
and move. This vibration absorbs or takes some of the energy away from the wave and less of the energy is
reflected. One example of absorption is black pavement which absorbs energy from light. The black pavement
becomes hot from absorbing the light waves and little of the light is reflected making the pavement appear
black. A white stripe painted on the pavement will reflect more of the light and absorb less. As a result the
white stripe will be less hot. Also, like what happen in Ocean waves that reach the shoreline, most of its energy
is absorbed by the shore.
