Objective 5 Waves
1. Demonstrate wave types and their characteristics through a variety of activities
such as modeling with ropes and coils, activating tuning forks and interpreting
data on seismic waves 10th grade only
2. Demonstrate wave interactions including interference, polarization, reflection,
refraction and resonance within various materials 11th grade only
Waves are a means by which energy is transferred from one point to another. The two
main types of waves are transverse and longitudinal (also called compression).
In a transverse wave, the medium vibrates in
a direction at right angles to the direction the
wave travels.(up and down)
In a longitudinal or compression wave, the
medium vibrates parallel to the direction the
wave travels.(back and forth)
Transverse waves: vibrate at right angles to the direction of travel (up and down
motion. (visible light, Infra Red light, Ultra Violet light, gamma rays, x-rays, AM-FM
radio, microwave, etc.
Wave in ballgame: At the ballgame, someone in the stands may start up a "wave" by
standing up and then sitting down. The people on one side then stand up and sit down,
then the next people, and so one. Everyone is still in their seats, but the wave traveled
through the ballpark from one end to the other.
Rope or string: You can shake a rope, causing a wave motion. The parts of the rope
only move up-and-down, but the wave moves from one end of the rope to the other. A
guitar string also has this type of motion.
Compression waves or Longitudinal waves: Back-and-forth motion creates
compression or longitudinal waves (while longitudinal waves vibrate in the same
direction as they travel). Longitudinal waves need a medium in which to travel. They
cannot exist without one. Sound can not travel in a vacuum.
Slinky
You can stretch out a Slinky along the floor and give one end a back-and-forth shove.
The compression will move along the Slinky to its other end.
Sound waves
A loudspeaker cone moves back-and-forth to create a sound, which is a compression
wave.
AC electricity
Electrons move back-and-forth in a wire, sending a wave of electric power through the
wire. The electrons stay in their general region in AC electricity, while the flow through
and out the wire in DC electricity.
Circular wave: There are cases where the material moves in a combination of
transverse and compression, moving in a circular or elliptical pattern.
Water waves
Drop a stone in a pool and waves move outward. The surface of the water looks like it
goes up and down, but actually the water molecules move in a circular or oval motion the
form the wave.
Seismic waves. Seismic waves are produced by
earthquakes. There are three types of seismic waves:
primary waves, secondary waves, and surface waves.
Primary waves (or P waves) are longitudinal waves.
They travel faster than the other types of seismic waves.
Secondary waves (or S waves) are transverse waves.
Like P waves, S waves can travel through solid rock, but
unlike P waves, they cannot pass through Earth’s liquid
core. Surface waves travel along the boundary between
the ground and the air. They are the slowest type of
seismic wave, but they can do the most damage.
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Amplitude is the height of a wave from the resting position. . As the energy of a
wave increases, amplitude increases.
The frequency represents the number of waves that pass by a point every second.
As the energy of a wave increases; frequency increases.
Wavelength is the distance between two corresponding points on a wave. As the
energy of a wave increases, wavelength decreases.
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The wave equation: The speed of a wave is given by the equation v = f λ
Where v is the speed of the wave measured in m/s, f is the frequency of the wave
measured in Hz and λ is the wavelength of the wave measured in m.
Students should have ample practice with this equation, as it will be one of the given
formulas on the TAKS test. As they found out in the activity, students should know that
as the frequency of a sound wave increases, so does its pitch.
Refraction/ Reflection
Reflections
- means to bounce off a surface
Refractions
- means to bend through an object
Reflection involves a change in direction of waves when they bounce
off a barrier; refraction of waves involves a change in the direction of
waves as they pass from one medium to another; and diffraction
involves a change in direction of waves as they pass through an
opening or around a barrier in their path. Refraction, or bending of the
path of the waves, is accompanied by a change in speed and
wavelength of the waves
Interference
Constructive interference: If the crests of the original waves line up with one another, the
resulting wave will have a larger amplitude than either of the original waves.
Destructive Interference: Destructive interference can occur when the crests of one wave
line up with the troughs of another wave. In this case, the amplitude of the combined
wave is equal to the larger wave’s amplitude minus the smaller wave’s
amplitude. If the waves have the same amplitude, then the waves
cancel each other out.
Diffraction: When a wave meets the edge of an object, you would think some would go
straight ahead, while the blocked portion would be reflected or absorbed. What happens
right at the edge is that some of the wave wraps around the edge. This interesting
characteristic of waves is called diffraction
Polarized light and Filters
- light travels in waves that can go in different directions (up down, side side)
- if a filter with slits in only one direction is used , those waves traveling the other
direction will be blocked out
- polarized light is the light that makes it through those slits
- glare, the light that makes you squint, is mainly horizontal (sideways) waves and so
sunglasses are designed to
block out those light waves reducing glare
- filters block out certain wavelengths and allow only certain waves through
- these filters are used in photography for special effects